Lay Summaries Archive

Read Lay Summaries from previous volumes of Functional Ecology here:

Early View Lay Summaries

  • Nitrogen saturation in humid tropical forests after 6 years of nitrogen and phosphorus addition: hypothesis testing Chen et al
  • Arboreality and associated gravitational stress on blood circulation have influenced the evolution of tail length in snakes Sheehy et al
  • How is wood decomposition affected by nutrients in a tropical forest? Chen et al
  • Xylem vessel traits tell the timing of leaf emergence and senescence in native and non-native understory species of temperate deciduous forests Yin et al
  • Agriculture increases temporal variability of stream ecosystem functioning Tolkkinen et al
  • Plasticity in sexual size dimorphism Bonneaud et al
  • Subordinate plants and fungi: what happens when these minorities join the effort? Mariotte et al
  • Birth date predicts alternative life history pathways in a fish with sequential reproductive tactics Fagundes et al
  • An invasive plant evolves rapidly in response to changes in climate Colomer-Ventura et al
  • Wood mice select foraging site according to the extent of within-plant variability in seed characteristics Shimada et al
  • A portfolio effect of shrub canopy height on species richness along a competitive stress gradient Bråthen and Lortie
  • Stress, immunity, and energy use in snakes Neuman-Lee et al
  • Preferred nest-sites help female song sparrows successfully raise chicks in early spring conditions Germain et al
  • Moving Beyond Body Condition Indices as an Estimate of Fitness in Ecological and Evolutionary Studies Wilder et al
  • Jack of all foods or master of one: symbiotic bacteria determine the diet of an insect pest Wagner et al
  • Does history matter in plant interactions? Wurst & Ohgushi
  • Predicting drought tolerance for Amazonian forest trees Maréchaux et al
  • The double-edged sword of immune defence and damage control: Do food availability and immune challenge alter the balance? Stahlschmidt et al
  • Darwin’s dream: a manipulative experiment for measuring natural selection in animal populations Bartheld et al
  • Neighbour presence reduces root allocation Chen et al
  • Burn or rot: leaf traits explain why flammability and decomposability are decoupled across species. Grootemaat et al
  • Food availability and seasonal reproductive activation in a songbird Davies et al
  • Does size really matter in predicting bite force in bats? Senawi et al
  • Cane toad impacts native species reproduction Narayan et al
  • Bacterial diversity enhances plant growth Weidner et al
  • Investigating isotopic functional indices to reveal changes in the structure and functioning of benthic communities Rigolet et al
  • Convergence of three mangrove species towards freeze-tolerant phenotypes at an expanding range edge Cook-Patton et al
  • Stress, hormones, and blood- the devil’s in the details Goessling et al
  • Early life stages dictate the future: plant species sorting along water availability gradients Fraaije et al
  • How does a winter desert annual cope with two challenges in the desert: summer rains and winter rain unpredictability Martínez-Berdeja et al
  • How Energy Allocation Influences Reproductive Success in the Southernmost Breeding Mammal, the Weddell seal Shero et al
  • Active prey mixing as an explanation for polyphagy in predatory arthropods Marques et al
  • The genetics of plant-plant interactions Baron et al
  • UV radiation causes darkening of the larval cuticle, at the expense of adult immune function Debecker et al
  • Intensity, not strategy is key for estimating trait values Paine et al
  • Welcome neighbours: cooperative fish benefit from settling close to each other. Jungwirth et al
  • Diverse forests make efficient use of canopy spaced by the authors Jucker et al
  • Tree efficiency in resource use does not relate to tree ability to withstand drought Limousin et al
  • Blossom colour change decreases the costs of reproduction Pélabon et al
  • Root and leaf strategies synchronize in tropical montane forests in Borneo Ushio et al
  • Basking sharks and oceanographic fronts: quantifying associations in the north-east Atlantic Miller et al
  • Trade-offs between trans-generational transfer of nutritional stress tolerance and immune priming. Shikano et al
  • Evolutionary conditions for floral colour change by plants. Ohashi et al
  • Revisiting old hypotheses on nitrogen, water and mimicry in mistletoes. Scalon & Wright
  • Plant identity drives biocontrol bacterial ability Latz et al
  • A novel growth model evaluating Age-Size effect on long-term trends in tree growth. Matsushita et al
  • Fitness consequences of indirect plant defence in the annual weed, Sinapis arvensis. Gols et al
  • Vitamin E deficiency in last-laid eggs limits growth of yellow-legged gull chicks Parolini et al
  • Conquering the world in leaps and bounds: hopping locomotion in toads is actually bounding Reilly et al
  • Stored grain pest parents protect offspring from bacterial infection in both laboratory and natural populations. Tate & Graham
  • How to package information into feather color patches. Chaine & Lyon
  • Host-plant genetics determines the composition of associated insects. Barbour et al
  • Red is the colour: the effect of trap colour and trap-flower distance on prey and pollinator capture in carnivorous sundews. Jürgens et al
  • Behaviorally escaping the heat of climate change may lead to long term vulnerability. Buckley et al
  • Microbiome affects egg carotenoid investment, nestling development and adult oxidative costs of reproduction in Great tits. Jacob et al
  • The whitefly-associated facultative symbiont suppresses induced plant defenses. Su et al
  • Biocrust-forming lichens effects on soil nutrients and microbial abundances. Delgado-Baquerizo et al
  • Highway to the danger zone: costs of immune system activation in an invasive lizard. Brace et al
  • Plant aroma drives diversification of plant-herbivore-carnivore interactions. Yoneya & Miki
  • Links between metabolic rates and growth depend on food availability. Auer et al
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    Nitrogen saturation in humid tropical forests after 6 years of nitrogen and phosphorus addition: hypothesis testing

    Hao Chen, Geshere A. Gurmesa, Wei Zhang, Xiaomin Zhu, Mianhai Zheng, Qinggong Mao, Tao Zhang, Jiangming MoAn old-growth tropical forest. Photo credit: Yunting Fang.

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    Nitrogen (N) deposition is increasing globally causing N-saturation, where N input to forests exceeds plant and microbial demand. It has been hypothesized that this N saturation will cause increasing N leaching, nitrous oxide (N2O) emission and N transformation rates and cause limitation of other elements. However, this hypothesis has commonly been tested in temperate forests, but it is not well tested in N-saturated tropical forests.

    To test this hypothesis, we measured soil inorganic N, soil N mineralization and nitrification rate, soil N2O emission rate, and nitrate (NO3-) leaching rate in an N-saturated old-growth tropical forest in south China after 6-years of N and phosphorus (P) addition.

    The results showed that N addition indeed caused further N saturation, as indicated by a significant increase in soil inorganic N, N2O emission and nitrate leaching after N addition, however, N addition significantly decreased in situ rates of net N mineralization and nitrification. On the other hand, P addition significantly decreased soil inorganic N concentration, N2O emission and NO3- leaching, but it significantly increased the net rates of N mineralization and nitrification.

    Our study showed that long-term N deposition in tropical forest may not induce N-saturation symptoms as observed for temperate forest, and that P addition can alleviate N-saturation in such tropical systems; hence it provides new insight into the N-saturation hypothesis.

    Image caption: An old-growth tropical forest. Photo credit: Yunting Fang.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Arboreality and associated gravitational stress on blood circulation have influenced the evolution of tail length in snakes

    Coleman M. Sheehy III, James S. Albert and Harvey B. LillywhiteAn arboreal eyelash viper (Bothriechis schlegelii) resting on a branch in Costa Rica.  Photograph by Coleman M. Sheehy III.

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    Gravity is a pervasive force that can severely affect blood circulation in terrestrial animals, and these effects can be particularly pronounced in tall or long organisms such as giraffes and snakes. Upright postures create vertical gradients of gravitational pressures within circulatory vessels that increase with depth. In terrestrial animals, this pressure potentially induces blood pooling and edema in the lower-most tissues and decreases blood volume reaching the head and vital organs.

    Since their evolutionary origins about 100 million years ago, snakes have diversified into a wide variety of aquatic, burrowing, terrestrial, and arboreal habitats where they experience various levels of gravitational stress on blood circulation. At the extremes, these stresses range from low to none in fully aquatic species living in essentially “weightless” environments, to relatively high in climbing species, especially arboreal forms specialized for climbing trees. As a result, arboreal snakes exhibit many adaptations for countering the effects of gravity on blood circulation, including relatively tight tissue compartments in the tail. However, patterns of tail length in relation to arboreal habitats and gravity have not been previously studied.

    We obtained length data for 226 snake species representing almost all snake families to test the hypothesis that arboreal snakes have longer tails than do non-climbing species. We found that average tail length increased and average body length decreased with increasing use of arboreal habitats and that arboreal snake species had average tail lengths 3–4 times longer than those of non-climbing species. Snakes with longer tails have a higher percentage of elongate blood vessels contained within the relatively tight skin of the tail, which counters blood pooling experienced during climbing. Total body length appears to be constrained in arboreal species, and total body length in adult female arboreal snakes appears to be an evolutionary tradeoff that favors longer tail lengths over maximum production of offspring as arboreal habitat-use increases. Our findings provide evidence that long tails of arboreal snakes function, at least in part, as an adaptation to counter cardiovascular stresses on blood circulation imposed by gravity.

    Image caption: An arboreal eyelash viper (Bothriechis schlegelii) resting on a branch in Costa Rica. Photograph by Coleman M. Sheehy III.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    How is wood decomposition affected by nutrients in a tropical forest?

    Yao Chen, Emma J. Sayer, Zhian Li, Qifeng Mo, Bi Zou, Yingwen Li, Yongzhen Ding, Xiankai Lu, Jun Wang, Jianwu Tang and Faming WangWood decomposition patterns over time. Photo from Yao Chen.

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    Tropical forests represent a major store of carbon, a large proportion of which is contained in woody plant parts. The decomposition of woody debris plays an important role in the forest carbon cycle, so understanding what controls wood decay will help us determine how much carbon may be released from wood decay in future. Previous research suggests that wood decomposition is regulated in part by the availability of nutrients. This topic has recently received much attention because nitrogen inputs from the atmosphere are increasing dramatically in tropical regions as a result of human activities. To investigate how changes in nutrient inputs will affect the decomposition of woody debris in tropical forests, we conducted a fertilization experiment using branch segments from four common tree species in a lowland tropical forest in China .

    Fertilization with phosphorus increased decomposition rates whereas fertilization with nitrogen had no significant effect. We observed changes in the patterns of nutrient release from the decaying branches that highlight the importance of the balance of nutrients for decomposer organisms. Our results indicate that the decomposition of wood is primarily constrained by phosphorus availability in this tropical forest. Our study suggests that it may be possible to predict decay rates using the ratio of carbon to phosphorus in tropical woody debris. Additional work with more tree species is needed to determine whether the patterns we observed are more generally applicable.

    Image caption: Wood decomposition patterns over time. Photo from Yao Chen.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Xylem vessel traits tell the timing of leaf emergence and senescence in native and non-native understory species of temperate deciduous forests

    Jingjing Yin, Jason D. Fridley, Maria S. Smith and Taryn L. BauerlePhoto of the common garden at Syracuse University, Photo by Jason D. Fridley.

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    Non-native understory deciduous woody species tend to advance spring leaf emergence and delay autumn leaf fall compared to native species when growing among natives in temperate forests, whereby they can exploit temporally available resources, such as water, nutrients, sunlight and pollinators. This strategy can potentially enhance growth in non-native species, affect their distribution and abundance, and ultimately cause significant changes to native ecosystems. However, prolonged leaf display also subjects non-native species to possible disruptions in their water conducting cells, due to freezing during the periods of increased frost probability in early spring and late autumn, blocking the water-conducting pathway and disrupting normal water transport capacity. Little is known about how non-native understory species are able to maintain normal water transport for leaf display within this context.

    Xylem vessels are long hollow chains of dead cells, and can carry water from roots to leaves in a plant. Earlier spring leaf emergence in temperate deciduous trees has been shown to be related to narrower xylem vessels because narrower vessels are more resistant to freezing-induced disruptions. We examined the xylem vessel traits in different developmental stages of xylem formation, i.e. metaxylem (formed before true wood), earlywood and latewood, across 82 native and non-native understory deciduous woody species common to Eastern U.S. deciduous forests, and monitored their timing of leaf emergence and senescence during 2008-2010 in a common garden.

    We found that compared to the natives, non-native species possessed specific xylem vessel traits that facilitated their tolerance to frost and allowed them to extend leaf display in late autumn, such as larger metaxylem vessels, smaller latewood vessel diameter and a higher proportion of solitary vessels within early- and latewood. In the spring, native and non-native species exhibited similar dates of spring budbreak and leaf emergence, linked to their similar xylem vessel size and vessel area percentage (the proportion of xylem cross section occupied by vessels) within metaxylem and earlywood. Within both groups, species with earlier bud and leaf emergence had a higher vessel area percentage within metaxylem and earlywood, suggesting understory species need sufficient water to support their early spring growth, even at the risk of freezing-induced cavitation.

    Image caption: Photo of the common garden at Syracuse University, Photo by Jason D. Fridley.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Agriculture increases temporal variability of stream ecosystem functioning

    Mikko Tolkkinen, Heikki Mykrä, Annamari Markkola and Timo MuotkaImage provided by authors.

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    All biological communities exhibit variability over time but increased variability may indicate a disturbed ecosystem, even if species richness and mean rates of ecosystem functions remain unaltered. Most previous studies on temporal variability of biological communities have focused on biomass production, while variability in the rates of other ecosystem functions has gained much less attention. We measured leaf decomposition during three consecutive years in three types of headwater streams: naturally acidic streams, agricultural streams with moderate nutrient enrichment and non-impacted reference streams. Leaf decomposition is frequently used as an indicator of stream ecosystem functioning, based on the rationale that food webs of most headwater streams are fuelled by the autumnal input of leaves from riparian trees. Once in the stream, leaf litter is processed by invertebrates and microbes, particularly freshwater fungi. We surveyed the species composition of fungal decomposer assemblages on submerged alder leaves in all three stream types in each study year to test whether fungal community composition and leaf decomposition rates are more variable over time in human disturbed than in reference streams. Temporal variability of leaf decomposition was indeed higher in nutrient-enriched than in non-modified reference streams whereas human impacted and naturally acidic streams did not differ. Fungal assemblages in both agricultural and naturally acidic streams were strongly dominated by a few key species whereas non-modified reference streams supported communities with more even abundance distributions. Inter-annual variability of leaf decomposition rate was positively related to dominance, with more variability in streams where fungal assemblages were dominated by a few prominent species. Our results show that although the process rates and diversity of fungal communities are regulated partly by the same environmental factors (for example, stream water pH and agricultural nutrient enrichment), processes are more sensitive to human disturbances. We emphasize the importance of measuring not only the mean rates, but also, and perhaps even more importantly, temporal variability of ecosystem process rates in any attempt to assess the influence of human disturbance on ecosystem functioning.

    Image caption: Image provided by authors.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Plasticity in sexual size dimorphism

    Camille Bonneaud, Erin Marnocha, Anthony Herrel, Bieke Vanhooydonck, Duncan J. Irschick and Thomas B. SmithA sagrei Bimini. Image provided by authors..

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    Why do male and female animals differ in body size? Differences between males and females in body size, known as sexual size dimorphism (SSD), is one of the most fascinating and mysterious features of animals. Both different species, and different populations within a species, often vary notably in this feature, but the reasons have remained obscure. Many studies have focused on sexual selection being the primary factor driving variation in SSD. Sexual selection involves the selection of features that help to maximize reproductive success, either by attracting mates, or by outcompeting rivals of the same sex. But another possibility is that variation in resource availability, such as food, could explain much of the variation in SSD. For example, consider two populations that vary in food availability – if males and females differ in how rapidly they grow in response to increased food, then variation in food availability could explain among-population variation in SSD. We tested this hypothesis by integrating laboratory and field studies for different populations of the common Bahamian lizard Anolis sagrei. In this species, males are typically larger than females, but how much they differ varies among different populations. The Bahamas offers a wonderful test case because islands vary in size, which usually correlates with variation in food availability. We first performed laboratory studies which showed that the amount of food had a significant impact on male, but not female, growth. Then, in the field, we showed that the total amount of food biomass within an island explained variation in male, but not female, body size. Our data therefore offer a fairly simple explanation for variation within some species in SSD – namely, the amount of food available to them. This is an alternative view to the common explanation of sexual selection driving variation in SSD. Further, these findings provide support for the condition-dependence hypothesis, according to which the larger sex should display greater plasticity in growth in response to environmental conditions.

    Image caption: A sagrei Bimini. Image provided by authors..
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

    Subordinate plants and fungi: what happens when these minorities join the effort?

    Pierre Mariotte, Bjorn J.M. Robroek, Vincent E.J. Jassey, Alexandre ButtlerImage provided by authors.

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    Drought events are recurrent phenomena, which are predicted to increase over the next few decades. The response of grasslands to drought seems to be determined by both species diversity and community composition. According to the diversity-insurance hypothesis, diverse plant communities have a higher chance of containing species well adapted to drought. Indeed, many experiments have confirmed a positive effect of plant species diversity on community resistance to drought, but the underlying mechanisms remain unknown.

    In parallel, the subordinate insurance hypothesis suggests that highly diverse communities contain higher number of subordinate species, which are more resistant than dominant species to climate change conditions and can compensate for less resistant species. Earlier, it has been reported that subordinate species can improve grassland productivity during drought but, surprisingly, these species seemed not to possess a better physiological ability for water use efficiency. Therefore, we hypothesized that their role might be better found belowground.

    Using a combination of subordinate species removal and summer drought in grassland, we show that soil processes play a critical role in the community resistance to drought. Our results highlight that subordinate species shift the balance within the soil microbial community towards more fungal dominance. Fungal communities, promoted by subordinate species, were more resistant to drought and maintained higher rates of litter decomposition and soil respiration. These results emphasize that subordinate species play an important role in mitigating drought effects on soil ecosystem functions. Reciprocal effects between fungi and subordinate species explain also how subordinate species better resisted drought conditions.

    Our findings highlight interesting plant-soil feedback effects between subordinate species and fungi, which seem delayed in time following a perturbation. Indeed, we showed plant effects on soil under ambient precipitation, with subordinate plant species favoring fungal communities, followed by soil effects on plants under drought conditions, with more resistant fungal communities being able to improve the resistance and growth of subordinate species. Additionally our results extend the diversity-insurance hypothesis by showing that more diverse communities not only contain species well adapted to perturbations, but also species with higher impact on soil microbial communities and related ecosystem functions.

    Image caption: Image provided by authors.
    This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

     

     

    Birth date predicts alternative life history pathways in a fish with sequential reproductive tactics

    Teresa Fagundes, Mariana G. Simões, João L. Saraiva, Albert F. H. Ros, David Gonçalves and Rui F. OliveiraThe two alternative male morphotypes of the peacock blenny: bourgeois nest-holders (front) and parasitic female mimics (back).

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    In some species individuals of the same sex, usually males, can reproduce by adopting different behaviours, depending on factors such as body size. In this paper we studied the factors that determine the alternative mating tactics that males can adopt in a littoral fish, the peacock blenny (Salaria pavo). In this species two mating tactics occur: (1) larger males defend nests in crevices to which they attract gravid females to mate with; after spawning nest-holder males provide parental care to eggs until they hatch; (2) smaller males do not express the ornaments of males and instead mimic females, both morphologically and behaviourally, in order to get access to the nests defended by nest holders, and to sneak fertilizations. Here we report a long term (6 years) mark–recapture study, which demonstrated that these alternative reproductive tactics are sequential, that is younger and smaller males may act as sneakers but as they grow older and larger all behave as nest-holders. We also found that males may follow different developmental trajectories depending on their date of birth. Males born earlier in the breeding season get to their first breeding season with a larger size than males that born later in the season. Accordingly, the former express the nest-holder tactic from their first breeding season onwards, whereas the later reproduce in their first breeding season as sneaker males and subsequently switch to nest-holders. The occurrence of a birth date effect on the expression of alternative reproductive tactics leaves room for important parental effects that should be investigated in future studies.

    Image caption: The two alternative male morphotypes of the peacock blenny: bourgeois nest-holders (front) and parasitic female mimics (back).
    You can read the article in full here.

     

    An invasive plant evolves rapidly in response to changes in climate

    Ferran Colomer-Ventura, Jordi Martínez-Vilalta, Paolo Zuccarini, Anna Escolà, Laura Armengot and Eva Castells Plants at their native area in South Africa (left) grow under wetter and hotter conditions than those introduced into novel regions, for example Australia (right). Differences in climate are driving a rapid evolution of this invasive species. Pictures: Eva Castells.

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    Biological invasions are one of the largest problems affecting biodiversity at a global scale. The study of invasive species, however, can also provide us with information on the response of organisms to a changing environment. Current hypotheses predict that invasive plants can rapidly evolve when they encounter new environmental conditions. Contemporary adaptation, which is revealed by different plant characteristics in the native and invasive plants, could facilitate the invasion process. Here we have evaluated how invasive plants respond to simultaneous changes in climate and herbivory.

    Senecio pterophorus is a shrub from the daisy family native to the Eastern Cape in South Africa. This species was accidentally introduced into the Western Cape in South Africa, Australia and Europe 40-100 years ago. In their native habitats plants are subject to wetter and hotter summers than those in the introduced areas. Additionally, native plants are more attacked by herbivores than their invasive counterparts. All these differences could lead to changes in plant morphology after invasion.

    Seeds collected from the native and the three non-native regions were grown in an experimental field under similar environmental conditions. We had two objectives. First, we aimed to determine whether plants from different origins were genetically distinct for some traits related to plant performance, such as growth, leaf area or reproductive capacity. Second, we aimed to determine whether climate and herbivory measured at the collection sites played a role in this genetic differentiation.

    Plants from the non-native regions were smaller and had a lower reproductive output than plants from the indigenous area. Herbivory was not related to these changes in plant traits. In contrast, our results are consistent with the role of climate driving rapid evolution of the non-native plants. Understanding the mechanisms for rapid differentiation in response to novel climatic conditions improves our ability to explain the dynamics of biological invasions and also to predict the response of native populations under a climate change scenario.

    Image caption: Plants at their native area in South Africa (left) grow under wetter and hotter conditions than those introduced into novel regions, for example Australia (right). Differences in climate are driving a rapid evolution of this invasive species. Pictures: Eva Castells.
    You can read the article in full here.

     

    Wood mice select foraging site according to the extent of within-plant variability in seed characteristics

    Takuya Shimada, Akiko Takahashi, Mitsue Shibata, and Tsutomu YagihashiThe Japanese wood mouse, endemic to Japan, is a major consumer of acorns. When they found acorns, they carry and hide them mostly in the ground or under fallen leaves for future use. Photograph credit: Y. Suzuki.

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    In general, foods are not uniformly distributed for animals, but distributed patchily in their home range. In this situation, animals have to evaluate the quality of foraging patches and select one for foraging. An oak tree, for instance, forms a foraging patch for seed-eating rodents, where acorns (seeds of oaks) are the food resource. Characteristics of these resources often vary largely even within a foraging patch (an individual plant), which is known as within-plant variation. In such a case, how does the animal evaluate the quality of patches? One of the simple and widespread ideas is using the mean as a representative. Namely, the quality of a patch is defined as the mean of the quality of each resource (acorn), such as acorn weight or nutritional value. However, patches with the same mean but different variation may not be equal for animals. To best describe the quality of a patch, within-plant variation must be considered in addition to the mean values.

    In this study, we examined which trees the Japanese wood mouse (Apodemus speciosus) would select as a foraging patch for acorns of konara oak (Quercus serrata). Here, the mean, variance (spread of values), and skewness (tendency to extreme values) of within-plant distributions of two acorn characteristics (weight and tannin content) were used as indicators of the quality of patches, and we examined the relationships between these indicators and patch selection by the wood mouse. Tannins are a bitter tasting chemical, and most animals tend to avoid tannin-rich food.

    There was notable within-plant variation in acorn weight and tannin content, and significant among-individual variation was also observed. We found that wood mice preferred to forage beneath trees with a large mean and variance of seed weight and a small variance and skewness of tannin content. These findings highlight that, in order to understand ecological and evolutionary processes at work in plant-animal interactions, within-plant variation in seed characteristics must be considered as well as mean value.

    Image caption: The Japanese wood mouse, endemic to Japan, is a major consumer of acorns. When they found acorns, they carry and hide them mostly in the ground or under fallen leaves for future use. Photograph credit: Y. Suzuki.
    You can read the article in full here.

     

    Mechanisms and consequences of facilitation in plant communities

    A portfolio effect of shrub canopy height on species richness along a competitive stress gradient

    Kari Anne Bråthen and Christopher LortieImage provided by authors.

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    Biodiversity is a critical resource in ecosystems both ecologically and economically for humans. It is thus a pivotal challenge for ecologists to explain and predict the biodiversity of any given ecosystem. In this study we focus on how the biodiversity of plants in tundra ecosystems can be facilitated. In tundra ecosystems plants are exposed to low temperatures and strong winds and on top of this the plants are grazed by herbivores. Consequently, the presence of dominant tundra shrubs with woody canopies can facilitate other plant species to cope with both stressful environments and presence of herbivores. These shrub canopies protect against grazing and wind abrasion, provide a protective snow layer in winter, trap particles and seeds for soil formation and new species establishment in summer, and buffer against temperature extremes. We propose that this range of positive mechanisms be termed “a portfolio effect of shrub canopy height”, and thus that the presence of higher shrub canopies increases biodiversity. We find support for our prediction. Along the entire gradient from low productivity, stressed plant communities to higher productivity, more competitive communities, we find that greater shrub canopy height promotes biodiversity. More particularly we find shrub canopy height to promote biodiversity on top of a humped-back relationship between biodiversity and plant productivity (i.e. at low and high productivity levels biodiversity is low and at intermediate productivity levels biodiversity is high), and as such we also find support for a general theory explaining biodiversity, i.e. the humped-back relationship. Climate change is currently causing encroachment of shrub species into tundra ecosystems. This study suggests that a universal theory of biodiversity is at play also in tundra plant communities, and that shrub dynamics are a crucial additional element in understanding changes in tundra plant biodiversity. It is thus likely that including the presence and height of shrub dominants will improve predictive models of biodiversity.

    Image caption: Image provided by authors.
    You can read the article in full here.

     

    Stress, immunity, and energy use in snakes

    Lorin A. Neuman-Lee, H. Bobby Fokidis, Austin Spence, Marilize Van der Walt, Geoffrey D. Smith, Susan Durham, and Susannah S. FrenchA male Terrestrial Gartersnake (Thamnophis elegans).

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    Wild animals undergo resource limitations throughout their lives, and must allocate this limited energy to a variety of physiological functions, such as growth, response to stress, and immune functions. In infrequent feeders, such as many snakes, shorter term limitations may not be as critical. Stressors, commonly experienced by wild animals, can also affect resource allocation “decisions” when energy is limiting. When an animal experiences stress, adrenal steroid hormones (such as cortisol in humans) are released into the bloodstream. These hormones have many functions, but chiefly mobilize energy for use in the body. When an animal is chronically stressed, it may be continuously secreting these hormones and therefore mobilizing energy. This energy usage may become detrimental, especially if no new sources of energy are available.

    The objective of this study was to determine how infrequent feeders, such as gartersnakes, are affected by chronic stress and food restriction. We restricted food for six weeks in half of the animals in the study and chronically stressed half of the animals (half food restricted and half not) using restraint stress. At the end of the experiment, we measured energy metabolites (triglycerides, glycerol, protein, and ketone) and compared the metabolite levels to two physiological measurements (immune and stress response). Food restricted animals did not lose significant amounts of body weight over the six week period, but did have altered levels of the energy metabolites triglyceride and glycerol. Also, chronically stressed animals responded by releasing significantly greater amounts of adrenal steroid hormones during acute stress than animals not chronically stressed. Finally, chronically stressed snakes had a reduced ability to heal wounds and a combination of both food restriction and chronic stress resulted in suppressed innate immune function. This study provides evidence that energetic limitation and stress can result in interactive and dramatic changes in energy usage and storage as well as in physiological functions that are critical to maintain life.

    Image caption: A male Terrestrial Gartersnake (Thamnophis elegans).
    You can read the article in full here.

     

    Preferred nest-sites help female song sparrows successfully raise chicks in early spring conditions

    Ryan R. Germain, Richard Schuster, Kira E. Delmore, and Peter ArceseFemale song sparrow searching for nesting material. Photo credit: Sylvain Losdat.

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    Choosing the right location to raise offspring can have important consequences for an individual animal’s overall reproductive success. For North American songbirds that build open-cup nests in the potentially harsh conditions of early spring, breeding in higher quality habitat can reduce some of the costs associated with producing and caring for their young. With the potential hazards of early spring breeding like cold temperatures and heavy rainfall, come the rewards of greater offspring survival and more future nesting opportunities for the parent. Thus, any advantages available to breeding birds during this crucial reproductive stage could lead to important benefits over both the entire year, and their lifetimes.

    We used 38 years of nesting records from an island song sparrow (Melospiza melodia) population to determine the relative influences of preferred, high-quality nest-sites on early spring reproductive success. We found that females that used these preferred sites tended to lay their eggs earlier in the season, incubated their eggs more efficiently, and produced chicks that were more likely to survive and become breeders in the population the following year. We also investigated potential cues (relative warmth and food availability) by which female sparrows may select early season nest-sites. Preferred nest-sites were relatively cooler overall, likely due to greater vegetation cover than less-preferred sites, but also had indicators of greater caterpillar abundance, a key food source during the early spring. Our findings show that breeding in preferred, high-quality habitat may offer female sparrows a reproductive advantage by allowing them to produce and care for their young at a lower energetic cost to themselves. These results provide clear evidence of the importance of habitat quality on the success of animals living in seasonal environments.

    Image caption: Female song sparrow searching for nesting material. Photo credit: Sylvain Losdat.
    You can read the article in full here.

     

    Moving Beyond Body Condition Indices as an Estimate of Fitness in Ecological and Evolutionary Studies

    Shawn M. Wilder, David Raubenheimer and Stephen J. SimpsonCallipers used for measuring. Photo provided by authors.

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    Ecologists, physiologists and evolutionary biologists are often interested in measuring the state or condition of animals. One shortcut that has been taken to estimate condition is the use of body condition indices, which measure the mass of an animal relative to frame or skeleton size. For example, in humans, the Body Mass Index (BMI; mass / height2) has been used as a body condition index. However, BMI is only a coarse measure of body composition and people with the same BMI can have very different body composition (e.g., weight lifter vs. obese person). Similarly, body condition indices used in ecological and evolutionary studies of a range of other animals are coarse or poor estimates of body composition (e.g., the relative amounts of lipid, protein and other components of the body). Another problem with body condition indices is that they are often used as a surrogate for body lipid content. The lipid content of an animal can be important for health or fitness but there are many other characteristics that could also be related to health. Furthermore, high body condition values are often assumed to reflect high health or fitness. However, as we know from studies of humans, individuals with intermediate condition index values may have higher health or fitness than individuals with very high (e.g., obesity) or low (e.g., malnutrition) values.

    As a consequence of these problems with condition indices, we argue that biologists should abandon body condition indices in favor of more descriptive or detailed measures of the physiology or composition of animals. Methodological advances have resulted in a range of techniques to accurately measure many aspects of animal physiology and composition, including many noninvasive techniques. For example, in humans and many other animals, dual-energy x-ray absorptiometry can be used to provide an accurate and noninvasive measure of body lipid, lean mass and skeleton content. More accurate data on animal physiology and composition will provide us with a better understanding of the ways in which animals respond to their environment and the connections between behavior, physiology and ecology.

    Image caption: Callipers used for measuring. Photo provided by authors.
    You can read the article in full here.

     

    Jack of all foods or master of one: symbiotic bacteria determine the diet of an insect pest

    Steven M Wagner, , Adam J. Martinez, Yong-ming Ruan, Kyungsun L. Kim, Paul A. Lenhart, Allison C. Dehnel, Kerry M. Oliver, and Jennifer A. WhiteColony of Aphis craccivora infesting young locust tree (Robinia pseudoacaciae). Image provided by authors.

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    Unseen microbes can affect the patterns observed at the macroscopic level in nature, mediating ecological interactions among plants and animals. Many herbivorous insect species are found to feed on multiple plant species, yet individual insects often perform well on only a subset of these plant species. Because infection with specific microbes often correlates with the use of particular plants, there has been much speculation, yet limited experimental evidence, that microbes promote dietary specialization. Here we investigated whether bacterial symbionts influence the diet of the cowpea aphid, which feeds on diverse plant species, including economically important crops. We first show that cowpea aphid clonal lines, each isolated from a single female, vary in their ability to use different plant species, which in turn correlates with patterns of infection by particular maternally-inherited bacteria. We next focused on aphid clones that naturally performed better on locust trees than other plant species, and which were infected with a common insect symbiont called Arsenophonus. We used antibiotics to remove Arsenophonus from two aphid clones and found that elimination of this symbiont dramatically reduced performance on locust, while generally increasing performance on other plant species. In fact, the uninfected aphids from "locust-specialist" lines didn't perform any better on locust than alfalfa-specialist lines, indicating that the bacteria are a critical component for effective use of locust as a food plant. We also experimentally infected an alfalfa-specialist aphid line with Arsenophonus, which instantaneously improved aphid performance on locust and decreased performance on alfalfa, effectively transforming an alfalfa specialist into a jack-of-all food plants. Inherited bacteria, including Arsenophonus, are widespread in insects and periodically gained or lost by host insect lines through natural processes; our results show that such transitions can abruptly change the food plant range of an herbivore, either restricting or facilitating use of particular plant species. If these changes improve performance on economically important food plant species, inherited microbes have the potential to transform innocuous herbivores into pests of consequence.

    Image caption: Colony of Aphis craccivora infesting young locust tree (Robinia pseudoacaciae). Image provided by authors.
    You can read the article in full here.

     

    Perspective

    Does history matter in plant interactions?

    Susanne Wurst &Takayuki OhgushiMultiple interactions including galling midges, aphids, and ants on a willow, Salix eriocarpa.

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    Plants interact with a wide range of organisms above and below the ground. These spatially separated organisms can indirectly affect each other through changes in plant characteristics which do not stop at the plant level, but can also affect the zones of influence of the plants both above (the ‘phyllosphere’) and below ground (the ‘rhizosphere’).

    Here, we ask if biotic interactions of plants below- and aboveground can have long-term legacy effects on future biotic interactions. In other words: does the history of biotic interactions matter for future biotic interactions of plants?

    We propose that history (or legacy) effects are mainly transferred by changes in plant and/or soil characteristics. Changes in plant and soil characteristics caused by biotic interactions such as feeding on plant materials can be short- or long-term. For example, plants can react with a rapid defense response against feeders that often vanishes when the feeding ceases. This is seen as a short-term response. On the other hand, plants can also invest in new leaves or roots to compensate for feeding damage or translocate nutrients to unattacked plant parts. These are more long-term changes and are more likely to persist and affect future interactions of plants. In soil, carbon input into the rhizosphere can be changed in the short term and affect the activity of the microbial community in the rhizosphere, while litter quality changed by feeding may affect decomposition and soil biota communities in the longer term. We also ask about the potential consequences of long-term and history effects in terrestrial ecosystems. The fitness of plants, the composition of biotic communities and the functions of ecosystems may all be affected by past biotic interactions. We conclude that the history of past interactions should be included in studies on biotic interactions for a better understanding of the current community organization.

    Image caption: Multiple interactions including galling midges, aphids, and ants on a willow, Salix eriocarpa.
    You can read the article in full here.

     

    Predicting drought tolerance for Amazonian forest trees

    Isabelle Maréchaux, Megan K. Bartlett, Lawren Sack, Christopher Baraloto, Julien Engel, Emilie Joetzjer & Jérôme ChaveCredits: Isabelle Maréchaux.

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    Droughts are predicted to become increasingly frequent and intense in Amazonia, and empirical evidence for the vulnerability of Amazonian trees to drought has accumulated over the past decade. However, little is known about the mechanisms or the diversity of drought tolerance in tropical trees. Indeed, it has been difficult to quantify drought tolerance in tropical trees, due to a lack of consensus on a relevant tree functional trait, practical to measure for the hundreds of tree species occurring in tropical forests.

    One potential trait has been proposed recently: the leaf water potential at wilting or turgor loss point (πtlp), which determines the tolerance of leaves to drought stress. We estimated πtlp for 165 trees of 71 species, at three sites within forests in French Guiana, using a new method, based on a demonstrated association between πtlp and another trait, the leaf osmotic water potential at full hydration. This new method is much faster than the standard one. Our dataset represents a significant increase in information for tropical tree species.

    We found that πtlp varied little within species and significantly across species. Some species were much more drought tolerant than others. Measures for πtlp were consistent with the few direct observations of species vulnerability in long-term drought experiments in Amazonia. We also found that πtlp showed only a weak or no correlation with other commonly measured plant traits.

    The variability in πtlp among species indicates the potential for a range of species responses to drought within Amazonian forest communities. Vegetation models seeking to predict forest response to drought may profit from more direct measurements of hydraulics-related plant functional traits such as πtlp.

    Image caption: Credits: Isabelle Maréchaux.
    You can read the article in full here.

     

    The double-edged sword of immune defence and damage control: Do food availability and immune challenge alter the balance?

    Zachary R. Stahlschmidt, Madison Acker, Ilya Kovalko and Shelley A. AdamoFemale Texas field cricket. Photograph by ZRS.

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    Although immune resistance is necessary to kill pathogens, it may also cause damage to hosts. Thus, animal immune systems must adaptively balance aggressive immune resistance (ability to destroy pathogens) with infection tolerance (ability to withstand the self-damage caused by immune resistance). Insects offer unique insight into this balancing act because phenoloxidase (PO)-mediated melanisation is a key feature of immune resistance, but PO activation causes inevitable self-damage. The antioxidant glutathione (GSH) may reduce this damage, but high levels of GSH can impair melanisation. We first showed that GSH may be a mechanism of infection tolerance because GSH levels in crickets correlated with fecundity (egg-laying) despite bacterial growth—that is, crickets with high levels of GSH in their hemolymph (blood) were able to maintain reproductive output despite increased levels of bacterial infection. Next, we used crickets to examine whether the relative balance between a component of immune resistance (i.e., PO) and protection from self-damage (i.e., GSH) shifted due to food availability or immune challenge. Although GSH and PO were positively correlated with one another, the PO:GSH ratio was robust and not affected by food availability or immune challenge. Thus, increased investment in a mechanism of immune resistance may require an increase in GSH to reduce self-damage (i.e., increase infection tolerance). Chronic immune challenge led to greater tolerance of oxidative stress suggesting that repeated immune challenge up-regulates infection tolerance mechanisms. Food limitation led to reduced PO activity, but not GSH concentration. This result suggests that mechanisms of immune resistance may be more sensitive to food availability than mechanisms of infection tolerance. In sum, mechanisms of immune resistance and infection tolerance can be correlated, and they can be affected by food availability or immune challenge.

    Image caption: Female Texas field cricket. Photograph by ZRS.
    You can read the article in full here.

     

    Darwin’s dream: a manipulative experiment for measuring natural selection in animal populations

    José Luis Bartheld, Juan Diego Gaitán-Espitia, Paulina Artacho, Cristian Salgado-Luarte, Ernesto Gianoli and Roberto F. NespoloImage provided by authors.

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    Natural selection is one of the most important ideas in the history of science, but for a long time, testing it experimentally was elusive. As Darwin thought, natural selection was supposed to be too subtle to be accurately measured. However, ecologists and evolutionary biologists have shown that rapid evolution is commonplace, and that applying the appropriate procedures (e.g., using closed system such as islands, applying reciprocal transplant experiments) both the magnitude and shape of selection could be measured with precision.

    In order to characterize fitness profiles –that is, the shape of selection- individuals in animal populations need to be marked, measured and recaptured. We chose to do such an experiment with the garden snail, an animal easy to collect in large numbers and also easy to mark and recapture. Also, it is distributed over a broad geographic range.

    We tested one of the most important tenets of physiological ecology (and the one that shaped its development during the eighties and nineties): the assumption that energy allocation in organisms and populations is adaptive (i.e., a target of natural selection).

    To do this, we performed a reciprocal transplant experiment using distant populations, which were bred in captivity and then released (about 1500 snails) at both extremes of their range, 1300 kms apart. Before release, we measure a suite of physiological, morphological and life-history traits.

    Our results were surprising. The results in general are not consistent with the occurrence of local adaptation (i.e., higher fitness at home), and in spite of the very different climates of the original populations, we found that only two traits (energy metabolism and body size) were the target of selection. This strikingly homogeneous result suggests that some general rule for adaptive optimization exists in these snails.

    Image caption: Image provided by authors.
    You can read the article in full here.

     

    Neighbour presence reduces root allocation

    Bin J. W. Chen , Heinjo J. During, Peter J. Vermeulen, Hans de Kroon, Hendrik Poorter and Niels P. R. AntenTwo split-root pea plants sit on the edges of two pots and place their roots in both pots. Thus, each plant has access to the volume of two pots, and share soil nutrients with the neighbour.

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    Increasing evidence suggests that plants are able to detect the presence of belowground neighbours. Such detection allows them to change their investment strategies in root growth and seed production. However, there is a debate about the direction and extent of the associated changes. Several studies propose that plants should grow more roots even at the expense of seed production to defeat their opponents (neighbours). Evidently such findings would have large significance for agriculture where maximum seed production is often the objective. Yet, studies that documented these effects are confounded by the fact that pot volume and plant size were insufficiently accounted for.

    We developed an experimental approach in which the effects of neighbour presence and the effects of rooting volume and plant size are disentangled. We grew pea plants in the presence or absence of a belowground neighbour at a range of soil volumes, while providing equal amount of nutrients per plant. Then, we used a statistical approach that accounts for plant size, rooting volume and neighbour presence effects. We found pea plants were smaller and had less roots in the presence of a neighbour, which contradicts the above-mentioned results and suggests that neighbour-induced root overproliferation did not occur in our study.

    More broadly our results indicate that if the effects of rooting volume and plant size are not taken into account, the effect of neighbours on plant growth can be misinterpreted. Our results do help to reconcile various results of neighbour effects published in the literature, by reasoning what the effect of rooting volume would be in other published studies.

    Image caption: Two split-root pea plants sit on the edges of two pots and place their roots in both pots. Thus, each plant has access to the volume of two pots, and share soil nutrients with the neighbour.
    You can read the article in full here.

     

    Burn or rot: leaf traits explain why flammability and decomposability are decoupled across species.

    Saskia Grootemaat, Ian J. Wright, Peter M. van Bodegom, Johannes H. C. Cornelissen and William K. CornwellThe ignition of a leaf. Photo credit: S. Grootemaat.

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    When leaves fall from a tree basically two things can happen: the leaves will either be decomposed by soil organisms or, in fire prone areas, the leaves can burn in a wildfire. Different plant species have different leaf characteristics. It is generally accepted that leaf characteristics, like lignin and phosphorus-concentrations, drive the speed of the decomposition process. This means that some species have leaves that decompose faster than others, depending on their physical and chemical characteristics. In contrast, less is known about the effects of leaf characteristics on leaf flammability. In this study on 32 species from eastern Australia we investigated which leaf characteristics determine the flammability of species. Both leaf dimensions and chemistry affected the ease of ignition and the burning time of individual leaves. For example, species with thinner leaves or leaves consisting of less dense material ignited more quickly. Leaves with higher moisture content took longer to ignite. Species with large, heavy leaves burned for longer than smaller (light) leaves. Furthermore, species with higher nutrient concentrations had shorter flame durations, suggesting that nitrogen and phosphorus work as flame retardants.

    When we compared the sets of leaf characteristics driving decomposability and flammability respectively, we found no relationship between the two litter fates. This means that leaves that decompose quickly are not necessarily those that are most likely to burn or burn quickly. This study gives us important information because knowing which plant species (and leaf characteristics) make the vegetation more flammable, either directly or indirectly through litter accumulation as a consequence of slow decomposition, can inform fire behaviour models. The results can help to predict where a fire is likely to start and, once a fire has started, some estimates can be made of the likely fire intensity and spread. This can help policy makers, fire fighters and residents to make better informed decisions.

    Image caption: The ignition of a leaf. Photo credit: S. Grootemaat.
    You can read the article in full here.

     

    Food availability and seasonal reproductive activation in a songbird

    Scott Davies, Thomas Cros, Damien Richard, Simone L. Meddle, Kazuyoshi Tsutsui, and Pierre DevicheAn Abert’s Towhee. Photograph by Christofer Bang.

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    Many animals have an outstanding ability to forecast when they need to be in breeding condition, yet much remains to be learned about how they achieve this. Most temperate zone songbirds, in particular, have to be exceptional forecasters because their reproductive system is shutdown during the winter and, to be able to breed, must be activated in the spring. Activation involves dramatic rises in the secretion of reproductive hormones and gonadal growth. This process takes time, so songbirds need to start it well before they need to breed and use cues from the environment that forecast when suitable environmental conditions are approaching. For decades, scientists have recognized that food availability is important because seasonal reproductive activation takes longer if birds are energetically constrained. However, our understanding of the physiological mechanisms that link food availability to activation of the reproductive system is limited.

    To address this issue, we food-restricted captive adult male Abert’s Towhees, Melozone aberti, during reproductive activation. We investigated whether energy deficiency constrains multiple aspects of reproductive activation, in particular the growth of the testes. Since testis growth is the culmination of an endocrine cascade that begins in the brain, we also aimed to understand which steps of this cascade are affected by energetic constraint and, to do so, measured endocrine activity at all three points of this cascade (i.e., brain, anterior pituitary gland, and testes). Consistent with the majority of studies in songbirds, we found no effect of food restriction on testis growth. However, food restriction influenced plasma levels of hormones from all levels of the cascade responsible for reproductive activation.

    These results suggest that energetic constraint modulates reproductive activation not through changes in the growth of the testes, but through changes in the plasma levels of hormones. In other words, even when constrained by energy deficiency, male songbirds can morphologically enter breeding condition, but delay increasing reproductive endocrine activity. This delay may be beneficial as it presumably decreases the expression of energetically costly behaviors, such as aggression and singing, which are stimulated by reproductive hormones.

    Image caption: An Abert’s Towhee. Photograph by Christofer Bang.
    You can read the article in full here.

     

    Does size really matter in predicting bite force in bats?

    Juliana Senawi, Daniela Schmieder, Björn Siemers and Tigga Kingston Juliana Senawi with bats great and small from the study site, Krau Wildlife Reserve, Malaysia. At around 200 g, Cheiromeles torquatus or the Naked Bat is recognized as the largest insectivorous bat in the world, while Kerivoula intermedia or the Small Woolly Bat weighs a mere 3 g (less than a sheet of an A4 paper!!) and is one of the very smallest.  Photograph by Nurul Ain Elias.

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    Would you rather be bitten by a big dog or by a small dog? Neither, of course, but if you had to choose, which one would it be? According to researchers, bite force (bite strength) increases with size in most animals, so the small dog is likely the better bet! Previous research in South and Central America indicates this relationship holds in bats too – bigger bats bite harder than smaller bats. We wanted to test whether this was the case in Asian forests, where the bat fauna is equally diverse, but dominated by very different families of bats.

    So how do we measure how hard an animal bites without losing any fingers? The bats were encouraged to bite a pair of metal plates hinged at one end by a transducer, which converts the pressure of the bite to a readable output of the force. We recorded the maximum bite force and measures of size (body mass, forearm length, head width, head height and head length) of 35 insect-eating bat species captured in Krau Wildlife Reserve, Malaysia. The bats ranged in size from 3 g to 200 g and belonged to 7 families. We also measured jaw features responsible for generating bite force using museum specimens of the same species, and used these to calculate the mechanical advantage (jaw effectiveness) adjusted by the size of the species.

    So, did bigger bats bite harder? The answer was yes, but the relationship between size and bite force differed among the bat families. The effectiveness of the jaw (mechanical advantage) also played a role, regardless of the size of the bat. All 35 species of bats in this study eat insects in the same forest, so they have developed strategies to avoid competition. Having a different bite force than your neighbour may be one – while some species may focus on hard crunchy prey like beetles, others may specialize on softer fare like flying termites and moths.

    Image caption: Juliana Senawi with bats great and small from the study site, Krau Wildlife Reserve, Malaysia. At around 200 g, Cheiromeles torquatus or the Naked Bat is recognized as the largest insectivorous bat in the world, while Kerivoula intermedia or the Small Woolly Bat weighs a mere 3 g (less than a sheet of an A4 paper!!) and is one of the very smallest. Photograph by Nurul Ain Elias.
    You can read the article in full here.

     

 

Cane toad impacts native species reproduction

Edward J. Narayan, Tim S. Jessop and Jean-Marc HeroCane toads present within terrestrial breeding habitats of the endangered Fijian ground frogs (Photograph by Dr Edward Narayan).

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Invasive species, major drivers of global change, cause unprecedented impacts on biodiversity. Their influence is most apparent on small oceanic islands where invasive species are the main cause of extinction. Understanding the mechanisms that make invasive species devastating is central to addressing their ecological impacts on the islands. One idea is that colonization of “simple” small islands affords invaders greater capacity to diversify and intensify their ecological roles beyond those seen in their native or invaded continental distributions.

Here, we used natural and manipulative field experiments to test if density-mediated competitive interactions from the highly-invasive cane toad could cause indirect effects and fitness loss to a small island population of the endemic and endangered Fijian ground frog. Over 13 successive monthly field surveys we collected 5000 non-invasive urine samples and measured body condition, survival and reproductive success of the Fijian ground frog. Samples were then analysed for reproductive and stress hormones. These data provided detailed accounts of how exposure to high-densities of cane toads caused major alterations in the nutritional status, physiological stress and reproductive physiology of ground frogs in both field enclosures and natural habitats. Most telling was that ground frogs in high toad density enclosures experienced extremely poor breeding success.

Despite a wealth of knowledge on the cane toad’s ecological consequences in invaded continents, such as Australia, our results reveal them to have extremely novel ecological roles and consequences on islands. Clearly, our results demonstrated how invasive cane toad competition, through extremely strong indirect effects, triggers major physiological changes that led to the reproductive collapse in Fijian ground frogs. Further, our study suggests it is important to limit alterations to island habitats to reduce the strength of invader-native species interactions. Thus, our results provide a striking example of why invasive species can disproportionately impact island endemics to potentially increase extinction risk.

Image caption: Cane toads present within terrestrial breeding habitats of the endangered Fijian ground frogs (Photograph by Dr Edward Narayan).
You can read the full article here.

 

Bacterial diversity enhances plant growth

Simone Weidner, Robert Koller, Ellen Latz, George Kowalchuk, Michael Bonkowski, Stefan Scheu and Alexandre JoussetPhoto of thale cress (Arabidopsis thaliana associated with bacterial community of Pseudomonas spp. (taken by Simone Weidner).

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In order to grow, plants need to take up soil minerals such as nitrogen. Nitrogen is however often limited and when present locked in the soil matrix. To make nutrients accessible to the plant, soil particles have to be broken down by enzymes. Since plants are not efficient in doing this themselves, they have to rely on soil microbes to make nitrogen available. To ensure an optimal nitrogen supply, plants “hire” soil bacteria by pumping huge amounts of sugars into the soil. By doing so, they attract and feed a dense bacterial community that in turn produces the required enzymes. Feeding bacteria is a huge investment for the plant and the effort is only worthwhile if bacteria do contribute to the required functions.

In this study we wanted to know how this function of making nitrogen available is influenced by the diversity of the bacterial community. We performed an experiment in which plants completely depended on the nitrogen supply from the bacteria and added bacterial communities to the plant that differed in their diversity.

Our study shows that bacterial diversity is an essential driver for the feedback of investment to the plant. Bacteria living alone produce less enzymes, slowing down nutrient cycling and plant growth. Mixing different species causes the bacteria to upregulate enzymatic activity, probably as part of a strategy to exploit resources better than their competitors. This helps to make more nitrogen available, and enhances plant growth.

Alterations of soil bacterial diversity, for instance by poor agricultural management, may thus have deleterious effects on plant growth. We propose that preservation of soil microbial diversity should be taken into account when it comes to agricultural management strategies. In addition, we propose that soil microbial diversity could be enhanced by reintroducing the missing species in order to improve nutrient mobilization and minimize the need for fertilizers.

Image caption: Photo of thale cress (Arabidopsis thaliana associated with bacterial community of Pseudomonas spp. (taken by Simone Weidner).
You can read the full article here.

 

Investigating isotopic functional indices to reveal changes in the structure and functioning of benthic communities

Carinne Rigolet, Eric Thiébaut, Anik Brind’Amour and Stanislas F. DuboisHaploops nirae, a gregarious tubiculous amphipod (crustacean) species (top picture) colonizing muddy marine sediments and engineering a unique habitat (bottom picture) while largely affecting associated species assemblages.

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The number of species is a key element for ecosystem functioning. However, not all species play the same functional role and/or respond to changes in the same way. Approaches to study species functions and interactions are mostly based on morphology (e.g. size, shape) or behaviour (e.g. feeding guild, motility). Using many such biological traits, one can calculate functional indices. They measure a potential functional niche of species assemblage (community). We suggest using stable isotopic compositions of species to provide a realized functional niche. Indeed, stable isotopes (i.e. 13C and 15N) in species’ tissues are directly linked with the species’ diet. As a result, they reflect information about the use of the physical habitat (e.g. size, hydro-climatic conditions) and the use of its resources (e.g. diversity, foraging strategy), two crucial factors in defining the ecological realized niche. In this study, we examine the ecological significance of newly defined isotopic functional indices, using a large set of associated species from two marine benthic communities widely reported in coastal shallow waters: the common brittle star Amphiura filiformis community competing with the crustacean amphipod Haploops nirae community.

We showed that Isotopic Functional Richness (a measure of the extent of the community trophic niche) is higher in the Haploops community due to a higher diversity in food sources but also due to longer food chains. Isotopic Functional Evenness (the regularity in all species distribution) showed that the biomass originates from other primary production sources, besides the phytoplankton.

These isotopic metrics responded according to expectations, based on the extensive knowledge of those communities. They provide new insights into how the structure of energy accumulation as biomass between species is likely to underpin the structure of the communities.

Image caption: Haploops nirae, a gregarious tubiculous amphipod (crustacean) species (top picture) colonizing muddy marine sediments and engineering a unique habitat (bottom picture) while largely affecting associated species assemblages.
You can read the full article here.

 

Convergence of three mangrove species towards freeze-tolerant phenotypes at an expanding range edge

Susan C. Cook-Patton, Michael Lehmann and John D. ParkerBranch samples collected from adult trees (photo credit: Susan Cook-Patton).

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Although many species are moving around as the climate changes, they are not all moving at the same rate. To help explain why three species of mangroves are migrating northwards at different rates, we examined variation in their ability to tolerate freezing temperatures. We sampled mangrove adults and seedlings along most of Florida’s eastern shoreline and exposed them to freezing temperatures. We also measured a suite of leaf and branch traits to examine how plants were changing as they grew closer to the range edge. We found that black mangroves, the most northerly and fastest migrating mangrove species, showed the greatest freeze tolerance, followed by red, and then white mangroves, the least northerly and most slowly migrating species. However, freeze tolerance as well as other traits were not fixed within species, but instead varied systematically with latitude. Adults from black and red mangroves showed higher freeze tolerance towards the range edge, and the leaves of all three species became denser, tougher, and smaller in the north than in the south. Thus, freeze tolerance appears to determine where mangrove species can move and at what rate. As freeze events become more and more uncommon, these species are likely to continuing moving northwards, but at different rates, possibly breaking apart plant communities that historically co-occurred.

Image caption: Branch samples collected from adult trees (photo credit: Susan Cook-Patton).
You can read the full article here.

 

Stress, hormones, and blood- the devil’s in the details

Jeffrey M. Goessling, Heather Kennedy, Mary T. Mendonça, and Alan E. WilsonA sample blood smear from an adult Gopher Tortoise (Gopherus polyphemus) with an elevated heterophil:lymphocyte ratio consistent with an acute stress response. Image credit: J.M. Goessling.

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Who hasn’t been stressed out? Although one could easily define what it feels like to be under stress, few could quantify their level of stress. So, what is stress? In the strict sense, it is a term to describe the physical pressure on a system from an outside source. For example, the weight of a floor resting on an I-beam. Historically, biologists have used the tools of endocrinology to measure stress on animal populations (that is to measure the degree to which the environment is exerting pressure on individuals). Specifically, hormones aptly referred to as “stress hormones” have been measured in individuals, and compared between “stressed” and “non-stressed” populations. However, while convenient, recent studies have indicated that stress hormones may not be reliable in indicating if animals are exposed to long-term stressors. One new approach to measuring stress is quantifying relationships among cells of the immune system, as it is well-known that stressors can elicit a change in how the immune system functions. In this paper, we quantitatively synthesized relevant literature (in a meta-analysis) to compare the traditional measure of stress (stress hormone concentration) to the more novel measure of stress (proportion of white blood cells) in studies that have been published using both methods. We found that both measures are in fact increased in populations exposed to stress. However, an important difference between the two measures is how individuals physiologically adapt to stressors over time. Specifically, elevated stress hormones are reduced in response to long-duration stressors, up to a point where they reach levels of non-stressed populations. This reduction in response to stress was not seen in the white blood cell counts. This suggests that the immune cell measure remains elevated in populations that have been exposed to stressors for a prolonged period. Therefore, conclusions from our study indicate that the white blood cell parameter could be very useful as a tool to test whether populations have been exposed to long-term stressors, while stress hormone concentrations should be interpreted cautiously as they may not be indicative of responses to long-term stress.

Image caption: A sample blood smear from an adult Gopher Tortoise (Gopherus polyphemus) with an elevated heterophil:lymphocyte ratio consistent with an acute stress response. Image credit: J.M. Goessling.
You can read the full article here.

 

How does a winter desert annual cope with two challenges in the desert: summer rains and winter rain unpredictability

Alejandra Martínez-Berdeja Exequiel Ezcurra & Mauricio TorresRigid spineflower skeleton at the end of the growth season. Photo: Alejandra Martínez-Berdeja.

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The rigid spineflower (Chorizanthe rigida) is a winter desert annual that grows in the Mojave and Sonoran deserts. Most winter annuals disintegrate and disperse their seeds at the end of spring, but the dead spineflower plants form dry rigid skeletons that stay in the field for several years, releasing seeds in response to winter rain events. C. rigida’s unique dispersal mechanism seems to allow it to synchronize seed release with available soil moisture, a scarce and precious resource in deserts. However, in order to do so effectively, the plant needs to overcome two challenges. On the one hand, it has to be able to differentially respond to seasonal precipitation patterns and avoid germination after summer rains, when the scorching temperatures could kill them. On the other hand, the plants also face winter rainfall unpredictability in the desert: any single rain event that might cause seeds to germinate might or might not be followed by additional rainfall, putting germinated seeds at a risk of dying from dehydration.

Our study shows that the stalk that attaches the seeds to the plant in spineflowers is much thicker in bi-seasonal deserts with summer rains, allowing the plants to retain seeds beyond summer and release them to more favorable winter rainfall cues. Secondly, we found that seeds in C. rigida individuals from populations experiencing highly unpredictable winter rainfall are much more variable in size than those from more predictable desert sites. Subsequent germination trials showed that larger seeds need more water to germinate and therefore have lower short-term germination and display a more “cautious” germination strategy. Thus, highly variable seed sizes allow C. rigida individuals to exhibit a heterogeneous germination response in extreme deserts, thus avoiding the loss of large fractions of seeds after a false moisture cue. Our study shows how desert organisms can adapt to both rain seasonality and unpredictability through simple changes in reproductive morphology.

Image caption: Rigid spineflower skeleton at the end of the growth season. Photo: Alejandra Martínez-Berdeja.
You can read the full article here.

 

How Energy Allocation Influences Reproductive Success in the Southernmost Breeding Mammal, the Weddell seal

Michelle R. Shero, Riley T. Krotz, Daniel P. Costa, Julie P. Avery & Jennifer M. BurnsWeddell seal, photo provided by authors.

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The ability of animals to stay in good health despite drastically changing environmental conditions is important for individual survival and reproductive success. An animal that is in good health can catch enough food to maintain their own body mass, and gain weight in the form of fat (lipid) or lean tissue reserves. The allocation of ingested calories is regulated by a suite of hormones, such as cortisol, thyroid hormones, growth hormone, and insulin-like growth factor-1. In seals, both the condition of females at the end of their fasting period, and the amount of energy gained while at sea, may influence a female’s probability of producing a pup the next year, as females that are too skinny may not be able to start a pregnancy or carry a foetus to term.

Weddell seals (Leptonychotes weddellii) are the southernmost breeding mammal in the world, and they live and reproduce in an extreme and rapidly changing environment. During the austral summer, females give birth, nurse their pups, breed, and moult while also reducing foraging efforts. By contrast, during the winter and pregnancy, animals forage intensively. In this study, we assess whether females that end the moult in better health (larger, more lipid stores) are more likely to return with a pup the next year, and whether pregnant seals “prepare themselves” for the upcoming lactation period by gaining more fat during the winter than non-reproductive females. Surprisingly, our study showed that both reproductive and non-reproductive seals gained similar amounts of mass and lipid during winter foraging. However, pregnant Weddell seals gain less mass during gestation than other seal species, explaining why previous studies show they must forage during lactation. Post-moult females with higher thyroid hormone concentrations were more likely to produce a pup the next year. Similarly, decreasing level of cortisol (stress) and maintaining growth hormone across the winter was shown to correlate with higher pupping probabilities. This study suggests that multiple hormones involved with energy allocation may also be indicative of positive reproductive outcomes. Understanding physiological factors that influence the probability of reproduction is important for assessing the species’ vulnerability to changes in ecosystem structure.

Image caption: Weddell seal, photo provided by authors..
You can read the full article here.

 

Active prey mixing as an explanation for polyphagy in predatory arthropods

Renata Vieira Marques, Renato Almeida Sarmento, Felipe Lemos, Marçal Pedro-Neto, Maurice W. Sabelis, Madelaine Venzon, Angelo Pallini & Arne JanssenPicture provided by authors.

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The question of why some species specialize on one or a few food types, whereas others consume many, continues to puzzle scientists. The existence of both strategies suggests that there are advantages and disadvantages to being a specialist or a generalist. Advantages to consuming various foods are to enable balancing of nutrients in the diet or diluting toxins present in each food type. In either case, a mixed diet yields a better reproductive performance of the animal than a single diet. Indeed, for us humans this comes as no surprise as we fare better on a mixed, varied diet.

Although there are many studies on the effects of mixed diets in animals, only a few show that animals actively search for different food types to obtain a mixed diet. In most studies, the different foods are offered together, so that the animals have plenty of food in the same area and can obtain a mixed diet without any effort. In this paper, we show that two species of tiny predatory mites (adults smaller than 1 mm) perform better on a mixed diet of two prey species, herbivorous mites that are pests of a biodiesel plant (Jatropha curcas) in Brazil. We show that females of each of the two predator species produce twice as many eggs on a diet consisting of the two prey species than when feeding on either of the two prey separately.

Moreover, we also show that the predators actually actively search for a mixed diet. This was done in the laboratory by offering the predators each prey species on a separate leaf of their host plant and by connecting the two leaves using a plastic bridge. So in order to feed on a mixed diet, the predators needed to spend time and energy to cross the bridge. Indeed they did so when the two leaves contained different prey species and much less when both leaves contained the same prey species. So the predators do what is good for them albeit at a cost: they actively commute between the two prey patches so as to obtain a mixed diet, thereby maximizing their reproductive performance.

Image caption: Picture provided by authors.
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The genetics of plant-plant interactions

Etienne Baron, Julien Richirt, Romain Villoutreix, Laurent Amsellem and Fabrice RouxPhoto provided by authors.

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Plant-plant interactions like competition are ecological and evolutionary processes that deeply influence natural communities. Studying their underlying mechanisms may be a key to understanding the structure and functioning of plant communities, which may in turn help to predict the response of plant communities to global change. However, we are only beginning to understand the genetics of competition. Notably, the identity of the genes involved in plant competitive ability still deserves deeper investigation. This exciting challenge calls for a multidisciplinary approach at the frontier between evolutionary ecology and genomics.

In this study, we adopted an ecological genomics approach to test whether the genetics of competitive ability of a local population of the model annual plant Arabidopsis thaliana was dependent on the identity of the competitor species. In a common garden experiment, the response of 48 A. thaliana genotypes to competition was estimated by looking at a suite of nine plant traits (including a proxy of seed production) in six competitive environments: absence of competition, intraspecific competition and interspecific competition with four species frequently associated with A. thaliana in natural plant communities (i.e. Poa annua, Stellaria media, Trifolium repens and Veronica arvensis). In addition, the biomass of its corresponding competitor was estimated in order to quantify the competitive effect of A. thaliana.

We showed that variation in the identity of the competitor might promote maintenance of genetic variation of A. thaliana at the local population scale and species coexistence at the community scale. We also demonstrated that the optimal strategies of A. thaliana in response to competition depend on the identity of the competitor species. Finally, we found that the genomic regions associated with the response of A. thaliana to competition depend on the identity of the competitor. This genomic map allowed us to identify the candidate genes related to plant-plant interactions.

Image caption: Photo provided by authors.
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UV radiation causes darkening of the larval cuticle, at the expense of adult immune function

Sara Debecker, Ruben Sommaruga, Tim Maes and Robby StoksMale Azure Damselfly (Coenagrion puella). Photo credit: Robby Stoks.

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Many animals, just like humans, get a tan when exposed to the ultraviolet radiation (UV) in sunlight. This darkening of the skin or cuticle is a result of the accumulation of the molecule melanin, which absorbs the harmful UV radiation and protects the body from damage. In addition, melanin performs several other functions inside the body. In many invertebrates, for example, it is also an important component of the innate immune system, where it is used to encapsulate pathogens, such as bacteria and parasites, with the aim of neutralising them. This process is called “melanotic encapsulation”. The formation of melanin used for UV defence and for immune function relies on the same enzyme pathway and the same resources, which are taken up through the diet and therefore, their availability can be limited. Consequently, there might be a link, or even a trade-off, between the quantity of melanin used for UV defence and immune function. Furthermore, it has never been studied whether UV radiation can affect the immune system in an invertebrate. Additionally, in animals that have distinct larval and adult stages, such as insects and amphibians, little is known about the mechanisms by which stressors experienced in the larval stage affect the adult after metamorphosis.

In this study, we exposed larvae of the Azure Damselfly (Coenagrion puella) to UV radiation to evaluate whether UV affects the accumulation of melanin in the cuticle. After metamorphosis, we measured the strength of the immune system in adults as the melanotic encapsulation response. We found that larvae that were exposed to UV accumulated more melanin in their cuticle and metamorphosed later and at a smaller mass than animals reared without UV. After metamorphosis, they also had a reduced melanotic encapsulation response, constituting the first proof for UV affecting immune function in an invertebrate. Importantly, animals that accumulated more melanin in their cuticle as larvae had a more severely impaired immune function as adults, meaning melanin was traded off between its different functions. Therefore, we identified a new mechanism by which stressors experienced in the larval stage carry over to the adult stage.

Image caption: Male Azure Damselfly (Coenagrion puella). Photo credit: Robby Stoks.
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Intensity, not strategy is key for estimating trait values

C. E. Timothy Paine, Christopher Baraloto and Sandra DiazDr Claire Fortunel measures leaf toughness at Nouragues Biological Station, French Guiana.

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Functional traits are attributes of plants and animals that affect their rates of growth, survival and reproduction. They affect the responses of organisms to their environment, and also reflect the effects of the environment on organisms. For example, consider wood density, a commonly measured functional trait, which affects how stiff and strong an individual tree’s trunk is. If known for all trees in a forest, it also indicates how much carbon is stored within that forest. Thus, because of their myriad effects, functional traits are used to answer many questions about individual species and ecological communities. The challenge addressed in this paper is that, in species-rich ecosystems, it is very difficult to measure the functional traits of every species, as many of them are vanishingly rare. We report the optimal method for sampling trees to estimate the functional traits of diverse forests.

We began with nine hectares of tropical forest in French Guiana, in which eight functional traits had been measured on every tree. This gave us the true values of each trait in each plot. We then, using computer simulations, applied 12 different trait-sampling strategies. To take a few examples, some of the strategies emphasised very common species, others a range of sizes, and others particular clumps of individuals. Because we wanted to optimize the sampling of functional traits, we simulated applying the strategies over a range of intensities, from 1% of the individual trees up to 50% of them.

The take-home message is that the way to successfully estimate the distribution of trait values in a species-rich forest is through intense field sampling. In other words, the more trees you sample, the better your estimate of functional traits. Of less importance is the strategy applied. Increased sampling improved the performance of all strategies. Importantly, a commonly applied strategy, looking up trait values out of a database, yielded poor results, especially in estimating the variation in trait values within a forest. Our conclusion is that there is no substitute for extensive sampling to accurately characterize the distribution of functional trait values in species-rich forests.

Image caption: Dr Claire Fortunel measures leaf toughness at Nouragues Biological Station, French Guiana.
You can read the full article here.

 

Welcome neighbours: cooperative fish benefit from settling close to each other.

Arne Jungwirth, Dario Josi, Jonas Walker, Michael Taborsky  A group of Neolamprologus pulcher (to the left) getting ready to defend their territory against predators (two Lepidiolamprologus elongatus and a mastacembelid eel; to the right). During the experiments, predators were confined in a plastic tube to prevent fish from harming each other. Foto: A. Jungwirth.

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Many animals defend territories against each other, but still prefer to settle close to neighbours. This is difficult to understand, especially when neighbours frequently fight over shared borders, and when large aggregations attract many predators. These conditions are met in the African cichlid fish Princess of Lake Tanganyika (Neolamprologus pulcher). Groups of these fish cooperatively care for offspring, and fiercely defend their territories against neighbours, yet still prefer to settle close to other groups. This creates colonies of variable sizes that attract many predators, resulting in higher predator densities inside colonies than outside. Here we asked what potential benefits the fish might gain from seeking the proximity of competing neighbours. Using SCUBA diving in the natural habitat of these fish in Zambia, we presented groups with their main predator and measured the effort they invested in the defence of their territory. Defending against these predators is costly, involving expenditure of time and energy, and considerable risk. We found that groups settling close to neighbours reduced their attack effort against the presented predator. However, as close neighbours contributed heavily to predator defence, similar levels of anti-predator attacks ensued across the entire range of group densities. Apparently, these fish benefit from settling close to one another by communal anti-predator defence, which allows them to save time, energy, and risk when being attacked. Hence the Princess of Lake Tanganyika benefits from joining forces in defence against a mortal threat, which seems to outweigh the costs of fighting one another. Such effects may be widespread in animals breeding in colonies, where grouping is often costly while no obvious benefits seem to compensate for the observed harm. Even without coordinated behaviour, improved “safety in numbers” applies not only at the level of individuals, but also of groups.

Image caption: A group of Neolamprologus pulcher (to the left) getting ready to defend their territory against predators (two Lepidiolamprologus elongatus and a mastacembelid eel; to the right). During the experiments, predators were confined in a plastic tube to prevent fish from harming each other. Foto: A. Jungwirth.
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Diverse forests make efficient use of canopy spaced by the authors

Tommaso Jucker, Olivier Bouriaud and David A. CoomesCarpinus betulus growing in the understorey of a mixed-species forest patch in Bialowieza (Poland). Photo provided by the authors.

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There is increasing evidence that mixed-species forests are more productive and cycle key nutrients more efficiently than species-poor ones, providing a strong argument for safeguarding the biodiversity of these ecosystems. Yet the ecological processes which drive this positive association between diversity and ecosystem function remain poorly understood. One idea which has recently been gaining traction is that mixed-species forests may be able to use canopy space more efficiently than monocultures, and that this in turn explains their greater ability to intercept light and sequester carbon.

There are two reasons why mixed forests might efficiently exploit canopy space. The first is that combining species which position their leaves in complementary height tiers can promote the development of a multi-layered canopy. The second possibility is that because of decreased competition for light among neighbours, trees in mixture develop larger crowns compared to their counterparts growing in monoculture. As part of a European-wide project (www.fundiveurope.eu) exploring the effects of biodiversity on ecosystem function in forests, we measured the crown dimensions of nearly 13000 trees and used these data to test whether trees in mixture packed their crowns more densely and efficiently than those in monoculture. We found that across a wide range of forest types and different combinations of species, diverse tree mixtures were able to partition aboveground space much more efficiently than species-poor ones. Interestingly, this occurred primarily as a result of individual trees expanding the size of their crowns when growing in mixture, and not because combining trees of different species resulted in multi-layered canopies. Our study shows that species mixing promotes the development of denser and more structurally complex forest canopies, and provides an explanation for why diverse forest ecosystems tend to be more productive and have faster rates of nutrient cycling.

Image caption: Carpinus betulus growing in the understorey of a mixed-species forest patch in Bialowieza (Poland). Photo provided by the authors.
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Tree efficiency in resource use does not relate to tree ability to withstand drought

Jean-Marc Limousin, Enrico A. Yepez, Nate G. McDowell & William T. PockmanPlastic troughs that covered 45% of the plot area were used to exclude a fraction of the rainfall and simulate more intense drought in a piñon-juniper woodland of central New Mexico in the southwestern United States.

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Plants must acquire carbon, nutrients and water from the environment in order to grow and survive. An analogy exists between economics and plant functioning by which one can define resource use efficiency as the amount of carbon gained through photosynthesis per unit of water, nutrients and carbon spent or invested in the process. Opposing views exist, however, regarding the role of resource use efficiency in plant tolerance to water limitation. High water use efficiency may be seen as advantageous to withstand drought because it means that more carbon is acquired per unit water transpired. On the other hand, it may be seen as a conservative “water saving” strategy of drought sensitive species who cannot afford to spend water for a low carbon return and are thus less competitive when water is limited.

To examine how water use efficiency, nitrogen use efficiency and carbon use efficiency relate to drought tolerance we compared them between piñon pine and one-seed juniper in the southwestern United States. These two species are good models for the study because they differ markedly in drought tolerance and water use strategy. Piñon pine has exhibited extensive mortality over recent drought episodes, while co-occurring juniper has suffered much more limited mortality. We experimentally manipulated rainfall using plastic troughs that excluded a fraction of the precipitation in one plot, and sprinklers for irrigation in another plot. This resulted in three different drought intensities (partial rainfall exclusion, natural drought, and partial irrigation, from the driest to the wettest) for the two species in a common ecosystem.

Our results show that increasing water limitation increased water use efficiency in the two species. In other words, the trees maximize the efficiency of their use of the most limiting resource, i.e. water. This comes at the cost of lower nitrogen and carbon use efficiency as the water limitation of photosynthesis prevents the trees from making efficient use of their other resources. Differences were larger across treatments, in response to water limitation, than between the two species, which exhibited a convergence in resource use efficiency. We conclude that drought tolerance and survival in juniper is linked to its ability to keep performing photosynthesis under more intense drought, and not to a more or less efficient use of resources.

Image caption: Plastic troughs that covered 45% of the plot area were used to exclude a fraction of the rainfall and simulate more intense drought in a piñon-juniper woodland of central New Mexico in the southwestern United States.
You can read the article in full here.

 

Blossom colour change decreases the costs of reproduction

Christophe Pélabon, Lauriane Hennet, Richard Strimbeck, Hansen Johnson, William S. ArmbrusterDalechampia scandens blossom A) during the pollination period, and B) during seed maturation. C) Change in the colour of the bract over a period of approximately 10 days. (Photos C. Pélabon).

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Flowering plants invest significant amounts of energy in the development of flowers, seeds, and fruits. Structures such as petals and subfloral bracts are part of that energy cost and sometimes remain on the plant after they have served their primary function as pollinator attractants. This persistence may impose additional energy costs in the form of maintenance respiration or further developmental changes, which may include post-pollination colour changes. Consequently, it seems likely that these persistent structures may serve secondary functions during fruit and seed development. We addressed this question in a study of the neotropical vine Dalechampia scandens. In this species, male and female flowers are clustered in inflorescences (blossoms) that are subtended by two leaflike, showy bracts that are white during pollination, but turn green after closing around the developing fruits. The green bracts may conceal developing seeds from seed predators, but photosynthetic activity in the bracts could also provide a local source of carbon to the developing seeds. We tested this photosynthetic augmentation hypothesis by experimentally manipulating the bracts in hand-pollinated blossoms and comparing seed development among the treatments, and by measuring photosynthesis and dark respiration in blossoms with and without bracts, and before and after greening. When bracts were removed or their photosynthetic activity was prevented by shading, the blossoms produced smaller seeds than normal. Furthermore, the greening of the bracts sufficiently enhanced their photosynthetic activity to produce a positive energy balance for the whole blossom in the post-pollination period, that is, to at least partly offset the total cost of producing blossoms, fruits, and seeds. This energy benefit may explain why bract retention has appeared at least twice in the evolution of the Dalechampia genus, and is found in numerous species within the genus. Finally, this study illustrates how developmental and physiological flexibility can function in fine-tuning reproductive costs in the evolution of flowering plants.

Image caption: Dalechampia scandens blossom A) during the pollination period, and B) during seed maturation. C) Change in the colour of the bract over a period of approximately 10 days. (Photos C. Pélabon).
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Root and leaf strategies synchronize in tropical montane forests in Borneo

Masayuki Ushio, Yasuto Fujiki, Amane Hidaka and Kanehiro KitayamaMt. Kinabalu from the southern slope of the mountain. This picture was taken from Park Headquarter of Kinabalu Park at about 1,560 m above sea level (©M. Ushio). One of our study sites (Intermediate P site) is a forest in the bottom part of the picture.

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Tropical forest trees in Borneo are gigantic, despite the fact that tropical soils contain small amounts of nutrients such as phosphorus (P), which are necessary to maintain and construct plant bodies. To maintain and construct such huge bodies, trees must have effective acquisition of soil nutrients as well as efficient use of the acquired nutrients.

In this study, we analyzed the ability of trees to degrade organic phosphorus, which needs to happen before it can be absorbed by roots, and morphological characteristics (such as surface area, diameter and tissue density) of the roots of the major tree species in three tropical montane forests on Mt. Kinabalu, Borneo. We also investigated the relationship between root and leaf properties. The amount of phosphorus in the soil in the three forests varies greatly from rich to intermediate to poor.

We found that the ability of roots to degrade organic phosphorus and root surface area increased while root diameter decreased with decreasing soil phosphorus. The results suggested that root properties change in a way that allows plants to effectively acquire phosphorus from soils. Furthermore, we compared root properties with leaf phosphorus concentrations of a given tree species. Interestingly, root phosphorus-degrading capacity increased with decreasing leaf phosphorus concentrations. This finding suggested that efficient phosphorus-acquisition of roots simultaneously occurs with conservative P use by leaves. There are several hypotheses to explain the results. Roots might detect low phosphorus concentration of leaves, and then could increase their ability to acquire phosphorus. Another hypothesis is that leaves with low phosphorus concentrations are shed beneath the tree crown, and roots must increase their ability to acquire phosphorus from such low phosphorus substrates. The truth is not known yet, but synchronized root and leaf strategies could be adaptive in phosphorus-poor tropical soils.

In conclusion, root nutrient-acquiring properties change along the gradient of soil phosphorus concentrations in the tropical montane forests, and the changes in root properties are coordinated with the changes in leaf P concentrations. Such synchronized root and leaf strategies could contribute to the maintenance/construction of tall forests on P-poor tropical soils in Borneo.

Image caption: Mt. Kinabalu from the southern slope of the mountain. This picture was taken from Park Headquarter of Kinabalu Park at about 1,560 m above sea level (©M. Ushio). One of our study sites (Intermediate P site) is a forest in the bottom part of the picture.
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Basking sharks and oceanographic fronts: quantifying associations in the north-east Atlantic

Peter I. Miller, Kylie L. Scales, Simon N. Ingram, Emily J. Southall and David. W. SimsImage provided by authors.

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Basking sharks are the world’s second largest fish, and yet one of the most enigmatic species in the oceans. Relatively little is known about how they use their environment, and the ways in which they find sufficient foraging opportunities. As large marine vertebrates that feed exclusively on microscopic animal plankton, they require large volumes of food to survive. Basking shark populations in the north Atlantic are still recovering from the impacts of historical overexploitation, and remain threatened by increasing human pressure on the marine environment. A better understanding of their ecology is of great importance, both to our knowledge of how marine ecosystems work and for effective conservation.

Previous research has documented associations between basking sharks and ocean fronts – areas of the sea where two different water masses meet. Physical and biological processes that occur at fronts can lead to increases in plankton abundance, attracting marine predators such as the basking shark to forage at these features. However, the importance of these associations has not previously been established. Recent innovations in satellite remote sensing enable the detection and mapping of fronts in the surface ocean from space, and animal-mounted technologies can track the movements of sharks over timescales of weeks to months. This study combines these two technologies to investigate levels of association between basking sharks and ocean fronts in the north-east Atlantic.

Pop-off Archival Tracking (PAT) tags were used to track the movements of seven sharks during the regional surface sightings seasons (May – October) of 2001 and 2002. Satellite front mapping and statistical modelling reveal associations between these sharks and fronts in temperature and chlorophyll-a, a proxy for plant plankton abundance. Basking sharks appear to associate strongly with productive regions in which fronts develop frequently over the course of the summer, and with fronts that they encounter in real-time as they navigate their foraging seascape. Moreover, the persistence and strength of fronts appear to be important factors in their value as foraging features. These insights have clear implications for understanding the preferred habitats of basking sharks, and are useful in informing marine spatial planning and the management of human threats to populations in the region.

Image caption: Image provided by authors.
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Trade-offs between trans-generational transfer of nutritional stress tolerance and immune priming.

Ikkei Shikano, Miranda C. Oak, Olivia Halpert-Scanderbeg & Jenny S. CoryHigh population density of cabbage looper larvae reduces food availability and increases risk of disease transmission (photo by Michael Hrabar).

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If parents experience a stressful environment it can sometimes have a strong positive impact on how their offspring fare in a similar environment, in essence, preparing them for what's to come. For example, in some animals, malnourished mothers can produce offspring that develop better under poor nutrient conditions. Similarly, mothers infected by a pathogen can transfer antibodies to eggs or fetuses to protect their offspring against that same pathogen. This capacity is not restricted to vertebrates, even invertebrates have shown this ability, which is particularly interesting since they do not have the ability to acquire immunity via antibodies.

However, providing for your offspring so that they are better equipped to survive can be energetically expensive for the parent. Therefore, we asked if parents are exposed to two sources of stress, in this case nutritional stress and a pathogen, would they equip the offspring for both stressors or would they select one over the other?

We tested this idea using the cabbage looper moth, Trichoplusia ni, by exposing parents to a pathogen (a bacterium) and poor food quality. These stressors are likely to occur together because as the population increases, food sources become depleted and the likelihood of coming into contact with an infected individual increases.

The results were intriguing. Parents that were exposed to the pathogen produced offspring that were highly resistant to that same pathogen. Similarly, parents that were given poor food produced offspring that developed faster on poor food, but interestingly these offspring were also highly resistant to two different pathogens, even though their parents never encountered them. This means that nutritional stress can also act as a cue for higher disease risk in the next generation. Our key finding was that when the parents experienced both stressors, they produced offspring that were resistant to pathogens but did not grow faster on a poor diet.

We have shown that experiencing multiple stressors can be important and could alter the response of a population to infectious disease.

Image caption: High population density of cabbage looper larvae reduces food availability and increases risk of disease transmission (photo by Michael Hrabar).
You can read the article in full here.

 

Evolutionary conditions for floral colour change by plants.

Kazuharu Ohashi, Takashi T. Makino and Kentaro ArikawaVarious patterns of floral colour change. Photos by Kazuharu Ohashi (upper left, lower right) and Takashi Makino (upper right, lower left).

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Many of the 'adaptive' traits in animal-pollinated flowers occur in only some of the species within a taxonomic group. A typical example of such evolutionary pattern is floral colour change—the retention of old, non-reproductive, rewardless, but fully turgid flowers in an altered colour. This set of floral traits has been suggested as a plant’s strategy to enhance pollinator attraction from a distance while minimizing visits to non-reproductive flowers at close range. However, considering that most visually oriented pollinators would respond similarly to these aspects of floral display, the reason for the low prevalence of floral colour change in nature is unclear. /p>

We conducted a screening search for floral colour change in 219 flowering plants by quantifying the spectral alterations in petals while the flower is open and functional and translating the alterations into colour shifts through the eyes of insects. Using comparative methods that take account of shared evolutionary history, we further explored multiple possibilities that could account for the infrequent occurrence of floral colour change. An inspection of floral colour with UV-sensitive insect vision allowed us to identify more colour-changing species than previously noted. At the same time, many other species exhibited little or no colour change, even for insects. This interspecific variation in the degree of floral colour change was significantly explained by possible evolutionary benefits in interactions with bee pollinators, as well as constraints imposed by evolutionary history, biochemical aspects of pigments and functional requirements for post-changed colouration to maintain long-distance detectability while reducing close-range attractiveness. /p>

These results illustrate that an understanding of floral evolution requires the consideration of all possible causes of trait diversity in an integrative manner. In future, we plan to focus more closely on particular lineages and test the proposed hypothesis that floral colour change is a plant strategy to accommodate bees or comparable pollinators with memory-based spatial foraging, as well as the hypothesis that partial colour change in old flowers has evolved as a viable strategy to attract pollinators from a distance while deterring pollinators at close range.

Image caption: Various patterns of floral colour change. Photos by Kazuharu Ohashi (upper left, lower right) and Takashi Makino (upper right, lower left).
You can read the article in full here.

 

Revisiting old hypotheses on nitrogen, water and mimicry in mistletoes.

Marina C. Scalon & Ian J. WrightThe modified root (haustorium) of the mistletoe Muellerina eucalyptoides penetrating the bark of its host Eucalyptus hemastoma.

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Mistletoes are leafy parasitic plants, capable of photosynthesis, but completely dependent on their host plants for water and nutrients – which they “steal” by tapping into the vascular system (xylem) of host branches using a modified root (“haustorium”). Various hypotheses have been proposed to explain the characteristically high transpiration rates of mistletoes. The “N-parasitism hypothesis” posits that nitrogen is the key limiting nutrient for mistletoe metabolism thus fast transpiration is needed to obtain sufficient host N, and that low ‘water use efficiency’ (WUE) during photosynthesis is the result, particularly when parasitising hosts with low xylem N concentration. In a very different context, the "mimicry hypothesis" posits that, by having leaves that physically resemble those of their host, some mistletoe species (“mimics”) can deploy leaves with higher leaf N concentration than hosts yet avoid the higher vertebrate herbivory that would otherwise be expected. Although setting out to explain different phenomena the two hypotheses are linked via the focus on leaf N.

We tested these hypotheses at global scale using leaf N and δ13C data for 168 mistletoes-host pairs, from 39 sites sampled across all continents, except Antarctica (δ13C, the carbon isotopic signature, is an index of time-averaged WUE). We found no apparent link between mistletoe WUE and xylem N concentration in hosts (indexed via host leaf N concentration, or by whether or not hosts were N-fixers) and thus, no support for the N-parasitism hypothesis. However, the mimicry hypothesis was partially supported: mimic mistletoes showed higher leaf N concentrations than their hosts but, unexpectedly, only when growing on N-fixing hosts (presumed to invest heavily in N-based anti-herbivore defences; thus, this is a case of “Batesian” mimicry, i.e. one where a harmless species has evolved to imitate a harmful species).

Our findings suggest that N is not always the key limiting nutrient for mistletoes, or at least not the main nutrient driving faster transpiration. Further, we show for the first time that mistletoes – like their hosts – exhibit clear trait adaptations to environmental gradients. By reconsidering these issues at broad geographic scale and across a large number of species, our findings substantially modify current knowledge on the ecology and physiology of mistletoes and their hosts.

Image caption: The modified root (haustorium) of the mistletoe Muellerina eucalyptoides penetrating the bark of its host Eucalyptus hemastoma.
You can read the article in full here.

 

Plant identity drives biocontrol bacterial ability

Ellen Latz, Nico Eisenhauer, Stefan Scheu and Alexandre JoussetLolium perenne in a magenta box. Photo by Ellen Latz.

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Soil-borne plant pathogens represent a major threat to plant productivity. Breeding of resistant varieties is tedious and often inefficient, and current management strategies based on pesticide application have unknown side effects on the environment, soil fertility and human health. Interestingly, there are soil bacteria associated with plant roots that function as antagonists to plant pathogens by producing antibiotic compounds (biocontrol bacteria). However, factors controlling the production of antibiotic compounds are little understood. Plant specificity of biocontrol bacteria has been studied intensively, and bacterial effectiveness has been shown to be mediated by plant-induced shifts in rhizosphere (root-associated) microbial communities and plant-induced changes in the activity of biocontrol bacteria in producing antibiotic compounds. In grasslands primary production often increases with plant diversity and we hypothesised that, at least in part, this may be due to increased effectiveness of biocontrol bacteria in species rich plant communities. Unfortunately, information on plant-microbe interactions is based almost exclusively on plant monocultures, and little is known about plant identity effects in multi-species plant communities.

We investigated whether the activity of a root-associated bacterium in producing biocontrol compounds varies with plant identity in a plant diversity gradient. We set up a microcosm experiment with the model rhizosphere bacterium Pseudomonas protegens CHA0, an important biocontrol agent, and investigated effects of plant identity and diversity on the production of biocontrol compounds.

The expression of genes coding for biocontrol compounds was driven to a large extent by plant identity and persisted along the plant species richness gradient for all tested genes. Notably, the effect of plant identity varied between genes, indicating that plant species specifically impact bacterial gene expression.

Our results indicate that the presence of certain plant species in plant communities disproportionately impacts biocontrol traits expressed by rhizosphere bacteria, providing new insight into our understanding of the patterns driving plant health and productivity. We suggest that mixed cropping systems including certain key plant species may increase plant protection and thereby the sustainable management of agricultural systems.

Image caption: Lolium perenne in a magenta box. Photo by Ellen Latz.
You can read the article in full here.

 

A novel growth model evaluating Age-Size effect on long-term trends in tree growth.

Michinari Matsushita, Katsuhiko Takata, Gaku Hitsuma, Tsutomu Yagihashi, Mahoko Noguchi, Mitsue Shibata and Takashi MasakiJapanese Cedar plantation (photo provided by authors).

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To predict long-term changes in aboveground biomass and carbon stocks of forests accurately, it is essential to understand how intrinsic (e.g. size and age) and extrinsic (e.g. competition and resource status) factors affect tree growth. One of the major problems in understanding growth trends in long-lived trees is the difficulty of separately quantifying the effects of tree size and age. Because trees grow by accumulating tree rings, there is an axiomatic age-size correlation. Therefore, a tree growth model that can account for the complex growth-age and growth-size relationships is required to accurately identify long-term trends in tree growth, and to reliably predict forests’ responses to environmental changes. To address this issue, we develop a novel tree growth model. Our model assesses the trend in tree growth over time by explicitly partitioning the effects of age and size, while controlling for the covariation between them. The model is then extended to incorporate the effects of neighbourhood crowding and individual tree variation. To demonstrate our model, we apply it to long-term monitoring data from a mature (104-year- old) plantation of Japanese cedar. As a result, we observed a pronounced age-related decline in diameter growth. However, at each age, greater tree size was associated with higher growth rate. The growth-size curve predicted from the model became flatter with tree age, and the curve’s peak shifted rightwards as tree age increased. Although the relationships between growth, size and age in long-lived trees are very complex, we conclude that our growth model can reliably predict long-term trends in tree growth with respect to both age and size. In addition, the flexibility of our model will enable more robust testing of species-specific responses to long-term environmental changes.

Image caption: Japanese Cedar plantation (photo provided by authors).
You can read the article in full here.

 

Fitness consequences of indirect plant defence in the annual weed, Sinapis arvensis.

Rieta Gols, Roel Wagenaar, Erik H. Poelman, Marjolein Kruidhof, Joop J.A. van Loon & Jeffrey A. Harvey Cocoon of the solitary parasitoid wasp, Hyposoter ebeninus, (note the head capsule of the Pieris brassicae host caterpillar which is all that is left of the host). Bottom: cocoons (yellow) and the host caterpillar after egression of the gregarious (Cotesia glomerata) parasitoid wasps. (photo credits Tibor Bukovinszky, Bugs in the Picture ©. .

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Many plants produce volatile chemicals when attacked by herbivores. In the last two decades, many studies have investigated the role of these plant volatiles in attracting parasitoids and predators of herbivorous insects. The production of this attractive volatile ‘bouquet’ is often referred to as indirect defence strategy of the plant. However, the assumption that this enhanced attraction actually benefits the plant due to reduced herbivory has been rarely tested.

Parasitoids vary greatly in life-history traits that determine growth of their host following parasitism. For example, some parasitoids allow the host to grow while the parasitoid larvae develop inside of them, whereas others kill or paralyze the host immediately after parasitism. In addition, some parasitoid lay a single egg in a host (solitary life style) whereas others can lay broods of up to several hundred eggs per host (gregarious life style).

In this experiment we compared seed production and seed quality traits in a short-lived annual plant (Sinapis arvensis or charlock mustard) when free of herbivory, exposed to healthy unparasitized caterpillars or caterpillars that were parasitized either by a solitary (Hyposoter ebeninus) parasitoid or a gregarious one (Cotesia glomerata). Both parasitoid species allow the host, larvae of the large cabbage white butterfly, Pieris brassicae, to grow following parasitism, though not to the same extent, and both healthy and parasitized caterpillars feed on the foliage and the flowers of their food plant. We compared results obtained from experiments in the greenhouse and outdoors, as many researchers examining plant defences against insects conduct their experiments under controlled conditions in the greenhouse or laboratory.

Plants indeed benefitted from parasitism and the effects were slightly more pronounced when the caterpillars were parasitized by the solitary rather than by the gregarious wasp. This was caused by the greater reduction of feeding damage to the plant’s reproductive tissues by the former species. Results were only significant for the experiments conducted outdoors, illustrating the difficulties in relating experiments performed under controlled greenhouse conditions to more realistic field experiments.

Image caption: Cocoon of the solitary parasitoid wasp, Hyposoter ebeninus, (note the head capsule of the Pieris brassicae host caterpillar which is all that is left of the host). Bottom: cocoons (yellow) and the host caterpillar after egression of the gregarious (Cotesia glomerata) parasitoid wasps. (photo credits Tibor Bukovinszky, Bugs in the Picture ©. .
You can read the article in full here.

 

Vitamin E deficiency in last-laid eggs limits growth of yellow-legged gull chicks

Marco Parolini, Maria Romano,, Manuela Caprioli, Diego Rubolini & Nicola SainoYellow-legged gull chicks at hatching (photo credit to Marco Parolini).

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Mothers transfer to their eggs substances that have important effects on their offspring. However, in order to increase their reproductive success, mothers may favour particular eggs over others. For example, in birds the first eggs in a clutch are often of better quality than the eggs that are laid subsequently.

Vitamins are important components of the egg yolk where they accomplish crucial physiological functions. Vitamin E has a major role in protection against oxidative stress. Although the beneficial effects of physiological levels of vitamin E for organisms are well known, the consequences of variation in the concentration of vitamin E in the eggs are largely unknown.

In this study we tested if the injection of a physiological dose of vitamin E in the yolk has beneficial effects on growth of yellow-legged gull (Larus michahellis) embryos, resulting in larger body size at hatching. In gulls, the concentration of vitamin E declines with laying order of the three eggs which constitute the typical clutch, suggesting that mothers are limited in the amount of vitamin E they can allocate to the eggs and that they favour their first-laid eggs. For this reason, we expected that our experimental manipulation would enhance body size of chicks hatching from third eggs in particular.

Indeed, we found that chicks from vitamin E injected third-laid eggs were larger than chicks from control third-laid eggs, whereas chicks from first- and second-laid eggs did not benefit from vitamin E supplementation.

Yellow-legged gulls are known to adopt a so-called ‘brood reduction strategy’ whereby chicks from first- and second-laid eggs are favoured over those from third-laid eggs, which seldom survive. This strategy is thought to increase parental reproductive success by leading to larger investment in offspring which are most valuable from a parental perspective. Our results suggest that differential allocation of vitamin E to the eggs according to laying order is part of such parental favouritism strategy because it can contribute to a hierarchy of reproductive value among progeny members.

Image caption: Yellow-legged gull chicks at hatching (photo credit to Marco Parolini).
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Conquering the world in leaps and bounds: hopping locomotion in toads is actually bounding

Stephen M. Reilly, Stephane J. Montuelle, Andre Schmidt, Emily Naylor, Michael E. Jorgensen, Lewis G. Halsey and Richard L. Essner, JrAn American toad (Anaxyrus americanus) in mid bound about to land on his feet and jump again without stopping.   Photo credit: Steve Reilly.

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Early frogs evolved jumping and simply crashed landed on their bodies. Later frogs mastered the ability to land on their arms and folded up legs so that they were ready to jump again. Jumping was perfected as an escape behavior that became the primary mode of locomotion in this prolific vertebrate group.

Most semiaquatic frogs are ambush predators, using one or two powerful jumps to escape their own predators, but other frogs have become terrestrial and use repeated shorter hops as their primary way of moving over land in search of food. Hopping frogs have traded long jumps for camouflaged toxic skin to discourage predators, can survive and breed in drier terrestrial habitats, and have greater endurance for sustained hopping on land. The toads are the most successful group of terrestrial frogs in terms of both diversity and geographic distribution. They diversified rapidly in the Oligocene (34 to 23 million years ago), expanding across nearly all continents. Even today, the cane toad continues to illustrate the terrestrial prowess of toads as they invade new areas in the Caribbean islands, Florida, the Philippines and Australia where humans have introduced them.

While many studies have revealed the numerous terrestrial adaptations of toads, their sequential hopping behavior, per se, had not been studied. When we compared the kinematics, forces and field occurrence of single hops and multiple hopping sequences in toads we discovered a novel aspect of locomotion adaptation that adds another facet to their exceptional terrestrial locomotor abilities.

We found that bouts of repeated hopping are not a sequence of normal hops but a series of bounding strides where toads land on their extended feet and jump again without stopping. In addition, free-ranging toads appear to use bounding locomotion more frequently than single hops. Bounding has the advantage of maintaining velocity and producing longer jump distances, while cyclic bounding steps reduce energy expenditure.

This is the first case of the common use of a bounding gait outside of mammals. Bounding adds a key terrestrial locomotor trait that helps explain toads’ history of global expansion and the challenges to modern faunas as introduced toads rapidly invade new ecosystems today.

Image caption: An American toad (Anaxyrus americanus) in mid bound about to land on his feet and jump again without stopping. Photo credit: Steve Reilly.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Stored grain pest parents protect offspring from bacterial infection in both laboratory and natural populations.

Ann T. Tate and Andrea L. Graham Gregarine protozoa infect the gut of a flat grain beetle collected from a feed mill. Photo credit: Ann Tate.

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Adult insects that are exposed to bacteria can produce offspring that are more likely to survive if they, in turn, become infected with the same bacteria. This phenomenon of enhanced survival is known as “trans-generational priming,” and has previously been demonstrated for a variety of insect species in laboratory settings. Trans-generational priming has sparked substantial interest for its potential application toward understanding and even manipulating the progression of infectious diseases in wild populations of insects, including vectors of human and livestock diseases and the biological control of agricultural pests.

However, it is unclear whether the lessons learned from laboratory experiments can be extrapolated into our predictions for wild populations, which are subject to higher levels of genetic and environmental variability. In this study, we perform experiments on flour beetles (Tribolium spp.) to demonstrate that trans-generational priming against the biological pest control candidate bacterium Bacillus thuringiensis (Bt) enhances post-infection survival and alters development rates of offspring in both a laboratory beetle colony and a wild population infesting a grain elevator. The parallels between laboratory and wild populations are accompanied by an important caveat, however: wild beetles that were infected with a common gut parasite were not able to bequeath the enhanced anti-bacterial protection to their offspring. Because these gut parasites occur frequently in species of stored grain pests and other agriculturally and economically important insects, accounting for co-infection by multiple parasites will be necessary for predicting the impact of trans-generational priming on disease dynamics in wild insect populations.

Image caption: Gregarine protozoa infect the gut of a flat grain beetle collected from a feed mill. Photo credit: Ann Tate.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

How to package information into feather color patches.

Alexis S. Chaine and Bruce E. Lyon A male lark bunting showing off his dapper plumage during the breeding season (Photo by Bruce Lyon).

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Many animals communicate with each other using color patches whose size or color can indicate the quality or health of the signaler. In animals with more that one color patch, a question is whether each patch communicates different information or whether patches work together to reinforce the same information. To answer this question, researchers often focus on how other individuals respond to the signals, but another approach is to study whether the different signals link together and how they change over time. We studied lark buntings —the Colorado state bird—across five breeding seasons to understand what information male plumage color patches could provide. Male lark buntings settle aggressive contests by comparing their relative plumage coloration and female lark buntings choose their mates based on the color and size of male color patches. In fact, females differ in what they like across years, and this attention to detail helps them produce more young. To investigate whether different plumage patches provide similar or different information, we looked at patterns of color variation among males and how the combination of color patches changes from one year to the next. Overall, we found that the size and color of most plumage patches were typically not linked to the value of other patches and likely provide different information. As a result, males had a mix of different quality patches. In addition, males regrow new feathers once a year and the size and color of different patches changed independently across years, an indication these different patches do not simply provide the same information to an onlooker. Nonetheless, most males came back with reasonably similar versions of each color patch, which tells us that some of the qualities advertised in plumage are inherent to the individual bird. Finally, the fact that some plumage patches show similar changes across most years suggests that these signals are influenced by large-scale environmental effects like climate. Overall, we showed that a longer term view of plumage signals can reveal a lot about what information these signals can communicate.

Image caption: A male lark bunting showing off his dapper plumage during the breeding season (Photo by Bruce Lyon).
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Host-plant genetics determines the composition of associated insects.

Matthew A. Barbour, Mariano A. Rodriguez-Cabal, Elizabeth T. Wu, Riitta Julkunen-Tiitto, Carol E. Ritland, Allyson E. Miscampbell, Erik S. Jules, and Gregory M. CrutsingerInsect species associated with two different genotypes of coastal willow (Salix hookeriana).

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Just as people prefer different varieties of crops (e.g., Fuji vs. Red Delicious apples), insects prefer to feed on particular genetic varieties of the same plant species. Consequently, genetic variation within plants can result in different compositions of associated insect species. Surprisingly though, we don’t often know why these genetic varieties of the same plant species are attacked more by certain insects compared to others. Knowing why is critical for making predictions about how shifts in the genetic diversity of a plant population will have cascading effects on the species that rely upon them.

To figure out why, we conducted a detailed case study of 26 unique genetic varieties (genotypes) of coastal willow (Salix hookeriana), a dominant plant species that lives in coastal riparian and dune ecosystems of northern California. Specifically, we conducted surveys to identify insect species feeding on each willow genotype and how abundant each species was. We also screened the willows for 40 different traits that we suspected would influence how tasty they were (e.g., amount of toxins, nutrients, and water in leaves) and how much food and shelter they provided for the associated insects.

We often found that several traits were important in explaining the abundance of insects on the different willow genotypes, indicating that different insects might cue in on different aspects of the plants when choosing a host. In particular, there were more insects on larger plants, probably because they provided more food and shelter. We also found substantial variation among willow genotypes in the amount of toxins, nutrients, and water in their leaves. However, these traits were relatively less important than plant size, likely because many of the insects are specially adapted to feeding on willows and are able to tolerate variation in leaf chemistry. Despite measuring all of these traits, we still found that we were not able to fully explain why the composition of insect species varies with the genetics of their host-plant. This suggests that future research should consider other factors that may influence how an insect chooses a host-plant, perhaps including competition for food with other insects or avoiding being eaten.

Image caption: Insect species associated with two different genotypes of coastal willow (Salix hookeriana).
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Red is the colour: the effect of trap colour and trap-flower distance on prey and pollinator capture in carnivorous sundews.

Andreas Jürgens, Taina Witt, Amber Sciligo, Ashraf M. El-Sayed Two sundew species with red prey-trapping leaves:  Drosera arcturi (top), Drosera spatulata (bottom). Photos: Andreas Jürgens.

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Carnivorous plants feed on insects as an adaptation to nutrient poor soil conditions. Thus, the features of the prey-trapping leaves of carnivorous plants are very likely under strong selection pressure to optimize prey capture. The functional features of carnivorous plants’ traps such as colour of the trap leaves have been mostly interpreted as adaptations to capture prey. However, carnivorous plants that feed on insects run the risk that insects that are needed for pollination also land on the traps. Such a feeding habit may have negative effects on pollen import and export and in consequence on plant reproductive success. It is therefore assumed that the so called pollinator-prey conflict in carnivorous plants might play an important role in the evolution of trap features. In carnivorous plants with sticky leaves, such as Drosera and Pinguicula, the spatial distance between traps and flowers and also the colour of the traps likely play a role in attracting prey but they may also affect the risk of potential pollinators landing on a trap. It has been reported that red pigmentation in carnivorous plants may lure insect prey to traps. Indeed many carnivorous plants turn red when they are “hungry” (low in macronutrients). If this is the case the red colour of carnivorous plants can be interpreted as a way to attract more prey. However, this idea remains controversial because colour vision in most insects does not extend very far into the red part of the spectrum. For most insects it is difficult to distinguish red from green.

We tested an alternative hypothesis, namely that red pigmentation of the trapping leaves may reduce the risk of a pollinator-prey conflict. Experiments were conducted in a natural habitat of two sundew species (Drosera arcturi and D. spatulata) in the Southern Alps of New Zealand. Using model flowers and sticky model traps similar in shape to Drosera leaf traps, we investigated the effect of colour (green vs. red vs. white), and flower-trap distance (flower stalk length and leaf arrangement i.e. upright as in D. arcturi vs. flat ground rosette as in D. spatulata) on composition and abundance of insects landing and being trapped.

We found that flower-trap distance had no significant effect on the risk of pollinators being trapped. Model flowers higher above the ground received more pollinator landings probably because they can be better seen in the vegetation. Across all model traps the number of trapped pollinators was significantly lower in traps with red leaves compared to green ones.

Our results suggest that the typical red pigmentation of the trapping leaves in Drosera may be a way to protect pollinators from being attracted and captured. However, pollinator protection via red traps may come with a trade-off because total prey capture was significantly lower in plants with red leaves.

Image caption: Two sundew species with red prey-trapping leaves: Drosera arcturi (top), Drosera spatulata (bottom). Photos: Andreas Jürgens.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Behaviorally escaping the heat of climate change may lead to long term vulnerability.

Lauren B. Buckley, Joseph C. Ehrenberger, and Michael J. Angilletta Jr.Joe Ehrenberger making physiological measurements on a Sceloporus lizard.

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Moving through landscapes to select microclimates to regulate body temperatures is viewed as central for mobile organisms to escape the heat as climate warms. However, behaviorally avoiding the heat may reduce selection for heat tolerance. This could hypothetically reduce variation in thermal tolerance across the distribution of a widespread species. We used a model of optimal thermal physiology to demonstrate the potential for this outcome, known as the Bogert Effect, for fence lizards in the Sceloporus undulatus species complex. We provide the most thorough test of the Bogert Effect to date using physiological data for populations across the North American distribution of this lizard. Empirical data for seven populations demonstrate similar thermal tolerance among populations, consistent with the model's prediction in the case of effective behavioral thermoregulation. In an eighth population, from a region where behavioral thermoregulation should be less effective, we observed greater heat tolerance and poorer cold tolerance, as predicted by our model. We next examined the consequences of the Bogert Effect for long term vulnerability to climate change. Our model indicates that lizards can avoid heat stress through behavioral thermoregulation in the coming decades. But animals must devote energy to behavioral thermoregulation, reducing the time available for foraging and exposing themselves to predators when seeking sun or shade. The potential to behaviorally compensate for climate warming may decline rapidly, forcing organisms to rely on physiological adaptation. However, rates of adaptation may be too slow for the organisms to respond to climate warming once behavioral thermoregulation becomes ineffective. Our analyses bolster concerns that behavioral buffering, while beneficial in the short term, ultimately limits the physiological adaptation required to endure a warming climate in the long term.

Image caption: Joe Ehrenberger making physiological measurements on a Sceloporus lizard.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Microbiome affects egg carotenoid investment, nestling development and adult oxidative costs of reproduction in Great tits.

Staffan Jacob, Nathalie Parthuisot, Armelle Vallat, Felipe Ramon-Portugal, Fabrice Helfenstein & Philipp HeebGreat tit (Parus major). Image copyright Joris Bertrand.

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Microorganisms constitute the major part of the earth’s biomass and are remarkable in their diversity and ubiquity. Pathogenic microbes can modify their host’s allocation of resources, increasing the amount of resources allocated to protection at the expense of other fundamental tasks such as development and reproduction. In contrast, many beneficial microorganisms are essential for host digestion or nutrient synthesis. The host microbiome, defined as the whole community of microorganisms in contact with an organism, is thus expected to play a major role in species evolution, although experimental studies from natural systems are still lacking. Here we test whether the microbiome affects host reproduction in wild breeding Great tits Men(Parus major) by experimentally modifying their microbiome, by spraying the nests with liquid solutions that either promoted or inhibited the growth of bacteria. We show that the microbiome affects three important components of bird reproduction. First, if bacterial growth was inhibited, females reduced the amount of carotenoids deposited in eggs, a molecule with important anti-oxidant and immune-stimulant properties for nestlings. Second, nestlings grow faster and are bigger at fledging when exposed to lower bacterial densities. Finally, while reproduction is a costly activity that usually results in the excessive production of free radicals and therefore oxidative damage to the body, we show that modifying the bird’s microbiome can alleviate this oxidative cost of reproduction. Our study provides experimental evidence for a role of the microbiome in bird reproduction, demonstrating the major effect that the microbiome may have on the evolution of reproductive strategies and life-history traits.

Image caption: Great tit (Parus major). Image copyright Joris Bertrand.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

The whitefly-associated facultative symbiont suppresses induced plant defenses.

Qi Su, Kerry M. Oliver, Wen Xie, Qingjun Wu, Shaoli Wang, Youjun ZhangWhiteflies feeding on tomato stems. Photo provided by authors.

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Herbivorous insects and plants have engaged in antagonistic coevolution for hundreds of millions of years. This process has led to the evolution of novel defenses in plants and counter-measures in insects, and fueled the diversification of both species-rich groups. Plants deploy a range of tactics to contend with insect herbivory, including the synthesis of toxic and repellant chemistry. Herbivores, in turn, have countered with diverse responses, including the detoxification and sequestration of defensive plant chemicals. Chemical defenses against herbivores are typically orchestrated by the jasmonic acid (JA) signaling pathway, which often acts antagonistically with the salicylic-acid (SA) pathway triggered by microbial threats. Emerging evidence indicates that another tactic in the arsenal of insects that eat plants is the modulation of plant signaling pathways to curtail plant defenses.

Insect herbivores are also frequently infected with maternally-transmitted bacterial symbionts, which are increasingly recognized to influence important ecological interactions. Here we demonstrate that the heritable bacterium, Hamiltonella defensa, infecting the whitefly Bemisia tabaci MED, suppresses induced defenses in tomato, Solanum lycopersicum to the benefit of the herbivore. We show that feeding by H. defensa-infected whiteflies inhibits the induction of JA and JA-related defenses, and that suppression depends on the SA signaling pathway. We also found that saliva applications collected from H. defensa-infected whiteflies suppressed induced defenses, suggesting that salivary factors present only in symbiont-infected whiteflies were responsible. This finding represents a novel role for arthropod heritable symbionts and yet another means by which insects can counter plant defenses against herbivory.

Image caption: Whiteflies feeding on tomato stems. Photo provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Biocrust-forming lichens effects on soil nutrients and microbial abundances.

Manuel Delgado-Baquerizo, Antonio Gallardo, Felisa Covelo, Ana Prado-Comesaña, Victoria Ochoa & Fernando T. MaestreClose-up view of the lichens dominating biological soil crusts at the Aranjuez Experimental Station: Diploschistes diacapsis, Fulgensia subbracteata and Psora decipiens (white, yellow and pink thalli, respectively). Photograph by Fernando T. Maestre.

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There is a lack of knowledge on how particular species of biocrust constituents (e.g. soil lichens) affect microbial communities and nutrient availability in the underlying soil.

Here, we evaluated the effects of six biocrust-forming lichens (Buellia epipolia, Diploschistes diacapsis, Fulgensia subbracteata, Psora decipiens, Squamarina cartilaginea Squamarina lentigera) on microbial abundance and multiple variables associated with soil nitrogen (N), carbon (C) and phosphorus (P) cycling. We also evaluated whether the composition of lichen tissues (contents in C, N, P and polyphenols) is related to C, N, P availability and microbial abundance in soils.

We found strong species-specific effects of the lichens studied on C, N and P availability in soil, and on soil microbial abundance. Inorganic P and amino acids were the most important factors differentiating lichen microsites. These effects seem to be related to the C, N and P composition of the lichen tissues. For example, soils under D. diacapsis and P. decipiens, which had the lowest and highest C, N and P contents in their tissues, respectively, had the lowest and highest nutrient availability, respectively. We also found lichen species-specific effects on soil microbes. For instance, F. subbracteata and D. diacapsis were negatively related to the abundance of bacteria compared to bare ground areas.

Our results support the idea that, as found with vascular plants, biocrust-forming lichens have species-specific effects on soil microbial communities and C, N and P cycling. Thus, continuing to consider biocrusts as a single entity will only add confusion to our knowledge of how they control nutrient availability and microbial abundance in the ecosystems where this key community is prevalent.

Image caption: Close-up view of the lichens dominating biological soil crusts at the Aranjuez Experimental Station: Diploschistes diacapsis, Fulgensia subbracteata and Psora decipiens(white, yellow and pink thalli, respectively). Photograph by Fernando T. Maestre. For additional BSC pictures from Aranjuez click here.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

The whitefly-associated facultative symbiont suppresses induced plant defenses.

Qi Su, Kerry M. Oliver, Wen Xie, Qingjun Wu, Shaoli Wang, Youjun ZhangWhiteflies feeding on tomato stems. Photo provided by authors.

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Herbivorous insects and plants have engaged in antagonistic coevolution for hundreds of millions of years. This process has led to the evolution of novel defenses in plants and counter-measures in insects, and fueled the diversification of both species-rich groups. Plants deploy a range of tactics to contend with insect herbivory, including the synthesis of toxic and repellant chemistry. Herbivores, in turn, have countered with diverse responses, including the detoxification and sequestration of defensive plant chemicals. Chemical defenses against herbivores are typically orchestrated by the jasmonic acid (JA) signaling pathway, which often acts antagonistically with the salicylic-acid (SA) pathway triggered by microbial threats. Emerging evidence indicates that another tactic in the arsenal of insects that eat plants is the modulation of plant signaling pathways to curtail plant defenses.

Insect herbivores are also frequently infected with maternally-transmitted bacterial symbionts, which are increasingly recognized to influence important ecological interactions. Here we demonstrate that the heritable bacterium, Hamiltonella defensa, infecting the whitefly Bemisia tabaci MED, suppresses induced defenses in tomato, Solanum lycopersicum to the benefit of the herbivore. We show that feeding by H. defensa-infected whiteflies inhibits the induction of JA and JA-related defenses, and that suppression depends on the SA signaling pathway. We also found that saliva applications collected from H. defensa-infected whiteflies suppressed induced defenses, suggesting that salivary factors present only in symbiont-infected whiteflies were responsible. This finding represents a novel role for arthropod heritable symbionts and yet another means by which insects can counter plant defenses against herbivory.

Image caption: Whiteflies feeding on tomato stems. Photo provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Plant aroma drives diversification of plant-herbivore-carnivore interactions.

Kinuyo Yoneya & Takeshi MikiLady beetles (Aiolocaria hexaspilota) search for leaf beetles (Plagiodera versicolora) using willow volatiles.

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Plants enhance the production of chemical toxins and physical barriers when attacked by herbivores (direct resistance). Many plants have also evolved another strategy, crying for help through emitting a special blend of aroma, which might effectively attract bodyguard carnivores that exclude herbivores (indirect resistance).

A blend of aroma transfers information useful to carnivores, such as herbivore species identity and damage levels. However, due to its diffusivity, the information is inevitably leaked and exploited by the herbivores. Thus plant aroma affects not only carnivore but also herbivore behaviour, involving them in an 'information war'. Herbivores face a dilemma of choice between intact and damaged plants, and have to balance plant quality and apparency (how easily the plant is found) with predation risk. Carnivores face a dilemma of choice between lightly- and heavily-damaged plants, and have to consider plant apparency and herbivore quality.

In order to predict the consequences of this information war, we have developed a simple food chain model of plant-herbivore-carnivore.

Our model clearly demonstrated that levels of direct resistance and the amount of plant aroma were key determinants of herbivore and carnivore behavioural responses to plant aroma, as the consequences of co-evolution. Under a wide range of conditions, the model predicts that carnivores should choose the plant aroma from damaged plants, independently of damage levels. The model also predicts that herbivores should choose (or avoid) the aroma from damaged plants when the level of aroma emission is low (or high). These two results imply that the plant aroma is highly likely to function as an effective form of indirect resistance, repelling pest herbivores and/or attracting bodyguard carnivores. Intriguingly, when direct resistance level is too high, the plant aroma from damaged plants attracts herbivore but repels carnivores. These results also explained the roles of plant aroma in several contrasting plant systems, including willow trees, Lima bean, and wild tobacco.

Our new findings will advance our understanding of plant resistances as a driving force of evolutionary diversification of animal foraging behaviour and thus complexity in ecological network structure.

Image caption: Lady beetles (Aiolocaria hexaspilota) search for leaf beetles (Plagiodera versicolora) using willow volatiles.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Prey density and distribution drive the three-dimensional foraging strategies of the largest filter feeder.

Jeremy A. Goldbogen, Elliott L. Hazen, Ari S. Friedlaender, John Calambokidis, Stacy L. DeRuiter, Alison K. Stimpert, and Brandon L. SouthallPhoto by Ari Friedlaender under NMFS Permit: #14534-2.

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Predators use a suite of foraging strategies to maximize their energetic gain and support their metabolism. Foraging in aquatic vertebrates can be broadly categorized into particulate feeding, where single prey items are seized and ingested, and bulk-filter feeding that involves the capture and processing of large volumes of prey-laden water. Several animal groups have independently evolved a bulk-filter feeding strategy, including cartilaginous fish (e.g. whale sharks and basking sharks) and baleen whales. Many filter feeders exhibit a ram-feeding mode where animals use their forward locomotion to drive water into the mouth where filtration occurs.

Large bulk filter feeders have long been assumed to be indiscriminate "vacuums" of the ocean, slowly filtering water regardless of variation in prey distribution, but here we reveal tremendous plasticity of foraging strategies in the world's largest filter feeder, the blue whale (Balaenoptera musculus), which is strongly a function of prey density and depth. Blue whales exhibit a unique mode of ram feeding called lunge feeding which involves the intermittent engulfment of large volumes of prey-laden water that are commensurate with the whale’s body size. Lunge feeding is a high-drag, high intake filter feeding strategy that requires high prey density for energetically efficient foraging.

We simultaneously measured whale foraging behavior and the characteristics of their sole prey resource, krill. Our analyses found that blue whales exhibit much more acrobatic lunge feeding events when foraging on small, low-density, more patchily distributed krill. In contrast, when foraging on dense, deeper, and larger krill aggregations, blue whales increased lunge frequency and maneuvered less during each lunge. These data demonstrate a previously unrecognized range of adaptable foraging strategies in a large bulk-filter feeder. Because maneuvering and diving require significant amounts of energy, the variation in foraging behavior that we revealed has major implications for optimal foraging and bioenergetic models.

Image caption: Photo by Ari Friedlaender under NMFS Permit: #14534-2.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Links between metabolic rates and growth depend on food availability.

Sonya K. Auer, Karine Salin, Agata M. Rudolf, Graeme J. Anderson, and Neil B. MetcalfePhoto of brown trout. Copyright Sonya Auer.

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Metabolic rates determine the energetic cost of living and can differ dramatically between individuals. At the very minimum is an individual’s standard (or resting) metabolic rate (SMR) – the energy it must expend on the maintenance of tissues and bodily functions needed to sustain life. Metabolic rates are thought to have important impacts on fitness, but results thus far are equivocal. Some studies find a negative while others find a positive correlation between SMR and different measures of fitness such as growth and survival. These inconsistencies might arise because links between metabolism and fitness depend on environmental conditions. Consideration of an individual’s aerobic scope (AS), in addition to its SMR, might also improve our understanding of the links between energy metabolism and fitness. Aerobic scope (the difference between SMR and maximal metabolic rate – after exhaustive exercise) determines the extent to which an individual can increase its metabolic rate above SMR to finance key functions such as digestion, locomotion, growth and reproduction.

We examined the links between individual variation in both SMR and AS and growth rates of brown trout (Salmo trutta) under different levels of food availability. We measured the SMR and AS of 120 juvenile trout and then fed each fish either a low, intermediate, or unlimited food ration in individual tanks in the laboratory. After two weeks we measured how much they had grown and examined whether the growth rates of individuals differing in their SMR and AS depended on food level. We found that an individual’s SMR was not correlated with its AS but both metabolic traits affected growth. However, their effects depended on each other and also on food level. Growth was faster at higher food levels, but individuals with different SMR and AS performed differently at each food level such that there was no combination of SMR and AS that was associated with the fastest or slowest growth at all food levels. These results demonstrate the importance of AS in explaining growth rates and provide evidence that links between individual variation in metabolism and fitness can depend on environmental conditions, in this case food level.

Image caption: Photo of brown trout. Copyright Sonya Auer.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

A cross-seasonal perspective on local adaptation: Metabolic plasticity mediates responses to winter in a thermal-generalist moth

Caroline M. Williams, Wesley D. Chick & Brent J. SinclairImage provided by authors.

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Across latitudinal and altitudinal gradients, environmental conditions vary strongly. To cope with these changing conditions, populations of organisms may be adapted to their local conditions, allowing them to survive and thrive better in their home environment than would populations from other regions. In temperate regions, this local adaptation must serve the organisms across their whole lifecycle, but characteristics that enhance survival and performance in one season may be detrimental in other seasons. Thus, to understand local adaptation we need to look at survival and performance across seasons, but most studies to date have focused only on the summer growing season. We tested for local adaptation to winter conditions in a common species of moth, Hyphantria cunea, which occurs throughout North America in diverse thermal environments. We collected larvae from the northern edge and centre of their geographic range, exposed them to both northern and central winter conditions in the lab, and monitored their survival and performance throughout the winter and into the next spring. We found that indeed the populations were locally adapted to their winter environment, with higher rates of survival and larger size and carbohydrate reserves when overwintered at their home conditions. This suggests that climate change may disrupt populations of this moth from their optimal conditions, and that populations may suffer if winter and growing season temperatures become decoupled.

Image caption: Image provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Changing drivers of species dominance during tropical forest succession.

Madelon Lohbeck, Lourens Poorter, Miguel Martínez-Ramos, Jorge Rodriguez-Velázquez, Michiel van Breugel & Frans BongersThe study area in Chiapas, Mexico, where the landscape consists of a mosaic of agricultural fields, young secondary forest and old secondary forest.

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Tropical forests are celebrated for their high aboveground biomass and high tree diversity. Here we study secondary succession: the process of forest recovery after complete clearance of the vegetation for agriculture. This represents a natural gradient of biomass and diversity build-up. As the forest grows back over time, some of the species that are present in the forest manage to attain high biomass and become dominant, whereas other tree species remain rare. We ask whether such dominance is related to the characteristics of the species (functional traits) and what mechanisms drive species dominance. Is it environmental filtering, i.e. does the environment select for specific types of trees? Or is it limiting similarity, i.e. successful species tend to be specialists that differ from other dominants?. We answer these questions by studying tropical secondary forest in Chiapas, Mexico.

We found that in young forests with low overall biomass the trees that are dominant, even if they are from different species, all have similar light capture strategies. Thus at this stage the main mechanism explaining dominance is environmental filtering: only species with a specific strategy are best adapted to the prevailing (high light) conditions and will dominate the young forest. As the forest gets older, biomass increases and a dense canopy prevents sunlight from entering the understory. The fierce competition for light means that trees need to specialize to make optimal use of different light-niches to be able to thrive here. Now dominant species need to be different from each other in terms of their light-capture traits, a mechanism known as competitively-driven limiting similarity. By exhibiting different strategies many species are able to co-exist in an environment that is increasingly packed by trees and limited in resources such as light.

During the first 25 years after agricultural abandonment the importance of environmental filtering as a driving force fades away rapidly and the importance of light gradient partitioning for species dominance starts to emerge. Understanding what factors shape species dominance is relevant as mainly the large dominating trees in an ecosystem determine how the forest functions.


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