Lay Summaries Archive

Read Lay Summaries from previous volumes of Functional Ecology here:

Early View Lay Summaries

 

Plant virus infection protects host plants from herbivore attack.

Kerry E. Mauck, Erica Smyers, Consuelo M. De Moraes & Mark C. MescherCMV-infected (upper) and healthy (lower) Cucurbita pepo plants with insets of squash bugs (top) and aphids (bottom). Photos by K. Mauck.

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Plant viruses live within plant cells and most are spread to new host plants through feeding and movement of specific insects (vectors). Sometimes, infection has negative effects on the plant, such as reduced size or seed production. But infection can also change aspects of the host plant (its phenotype) that mediate interactions with other antagonists. Virus infection can alter host cues used by foraging insect herbivores (including vectors), such as color, smell, or taste. Some of these cues (color, smell) are also used by beneficial insects to locate herbivore prey. Despite the fact that virus infection is known to alter host phenotype, few studies have examined how virus infection changes plant interactions with non-vector herbivores and their predators.

In our study we used field experiments, behavior trials, and analysis of plant chemical and physical characteristics to understand the effects of a widespread plant virus, Cucumber mosaic virus (CMV), on the interactions of its host plant, squash, with non-vector herbivores and predators. Our previous work showed that CMV infection makes plants more attractive to their aphid vectors based on smell, but diminishes plant quality and palatability (encouraging vectors to disperse and spread the virus after picking it up from leaf cells). Here we found that CMV infection also reduced the likelihood of non-vector herbivores visiting, colonizing, and laying eggs on squash plants. Most notably, a highly damaging specialist herbivore was unable to recognize CMV-infected plants as good sites for egg laying. This reduction in herbivore levels was consistent with our analysis of plant characteristics, which showed that CMV-infected plants have lower levels of sugars and reduced size, making plants less palatable and less visually apparent. In contrast, predators and parasitoids were able to locate plants with prey regardless of whether they were infected or healthy. The combination of lower herbivore visitation with maintenance of predator visitation means that CMV-infected plants may experience reduced herbivore attack relative to healthy plants. This means that CMV-infected plants will be present in the landscape longer, possibly leading to more new infections, and that plants infected with CMV may even out-perform uninfected plants when herbivore populations are very high.

Image caption: CMV-infected (upper) and healthy (lower) Cucurbita pepo plants with insets of squash bugs (top) and aphids (bottom). Photos by K. Mauck.
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.

 

Invasive plants, thermal regimes, and habitat management for snakes.

Evin T. Carter, Bryan C. Eads, Michael J. Ravesi, and Bruce A. KingsburyIntroduced Japanese honeysuckle encroaching on copperhead habitat (photo credit to Evin T. Carter).

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In this new era of “global ecology”, plants and animals from around the world are becoming established where they previously did not exist. In some cases, they have become invasive, potentially altering how ecosystems function. Despite recognition that devastating effects can follow, there remains a shortage of evidence regarding broadly applicable mechanisms.

Here we examine the impacts of exotic invasive plants on a snake, the Northern Copperhead (Agkistrodon contortrix), in a site facing substantial infestation by exotic plants. We hypothesized that the denser growth patterns characteristic of exotic invasive plants lead to reduced and less variable temperature below the canopy. Consequently, the quality of the habitats would be compromised for ectotherms like the copperhead in a temperate forest landscape, where access to sunlight is key to maintaining suitable body temperature and proper metabolic function.

To test our hypothesis, we used physical models of snakes to measure environmental temperatures within native and exotic plant-dominated habitats (including 11 exotic species) in a temperate forest landscape in the Midwestern US. Using temperatures derived from models and temperature preferences of snakes in the laboratory, we generated estimates of the capacity for snakes to achieve preferred body temperatures within that landscape. To further test the effect of vegetation structure and the efficacy of targeted management, we also removed exotic plant foliage from eight 20 m2 plots while monitoring use of those areas by reptiles before and after manipulations.

We found that exotic plant-dominated habitats exhibited reduced and less variable temperatures compared to their native counterparts, with mixed-exotic habitats exhibiting the lowest temperatures overall and exotic shrubs (6 species) the lowest as a structural group. Radio-tagged snakes clearly avoided exotic vegetation at multiple scales. Response to exotic foliage removal was also rapid—including use of plots as gestation and birthing sites. Our results suggest a direct effect that is common to a broad range of invasive plants in a variety of ecological contexts. Because eradication of many invasives is unlikely, we suggest that targeted thinning is a cost-effective means of partially alleviating this challenge in compromised landscapes.

Image caption: Introduced Japanese honeysuckle encroaching on copperhead habitat (photo credit to Evin T. Carter).
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.

 

Wolves that are heavily hunted have higher stress and reproductive hormones than wolves with lower hunting pressure.

Heather M. Bryan, Judit E. G. Smits, Lee Koren, Paul C. Paquet, Katherine E. Wynne-Edwards & Marco Musiani Two wolves in Alberta run across a frozen lake away from an approaching helicopter. Photo credited to Paul Paquet.

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In parts of the world where they remain, wolves play a key role in maintaining healthy ecosystems. Yet wolves are also viewed as competitors with people over shared prey and livestock. Consequently, wolves are often subject to management that includes population reductions of up to 50% per year, with occasional reductions up to 90% during intensive control. Wolves have a sophisticated social system with typically one breeding female per year. On-going and substantial reductions can disrupt wolf social structure, leading to increased reproductive rates and altered genetic structure and behavior. Despite these profound effects on surviving individuals, little is known about the influences of population reductions on wolf physiology.

Accordingly, we applied the novel approach of measuring hormones in hair to investigate the physiological effects of hunting on wolves subject to different hunting pressures in Northern Canada. Stress and reproductive hormones, including cortisol, progesterone, and testosterone, are accumulated into growing hair from the blood vessel that supplies the hair follicle and surrounding glands. Our measurements of hair revealed that wolves from a heavily hunted population in the tundra-taiga had higher progesterone compared with lightly hunted wolves in the boreal forest. Elevated progesterone could reflect a higher proportion of breeding females, which might occur if normal pack structure is disrupted by hunting. Similarly, heavily hunted wolves had elevated testosterone and cortisol (a stress hormone), which may reflect social instability caused by hunting.

Ecological differences between the two populations could also affect hormone levels. Therefore, we controlled for habitat by examining another population of wolves from the boreal forest killed during an intensive control program. Lack of sex data precluded examining testosterone and progesterone in this population; however, we found that similarly to tundra-taiga wolves, forest wolves from the control program had elevated cortisol compared with forest wolves that were lightly hunted. Although the long-term effects of chronically elevated stress and reproductive hormones are unknown, there are potential implications for wildlife health, welfare, long-term survival, and behaviour. Therefore, our findings emphasize that conservation and management plans should consider not only numeric responses, but also possible social and physiological effects of control programs on wildlife.

Image caption: Two wolves in Alberta run across a frozen lake away from an approaching helicopter. Photo credited to Paul Paquet.
This article is available here.

 

Starling males show their ability to cope against bacteria to females.

Magdalena Ruiz-Rodríguez, Gustavo Tomás, David Martín-Gálvez, Cristina Ruiz-Castellano and Juan J. SolerThe picture shows the ornamental feathers of the starling male. Credits: J. J. Soler.

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Spotless starling males have special, ornamental feathers in their throat that are longer and narrower than the rest of their plumage, and also than female throat feathers. During the courtship period, males sing in highly visible places, with the head and bill raised. This position exposes the special throat feathers, which are very conspicuous and moved by the wind. It was previously shown that those males with larger throat feathers have also a better reproductive success, since they are preferred by females.

We have found that these special feathers have a different susceptibility to degradation by feather-degrading bacteria than the other male and female throat feathers. The basal part of these feathers is highly resistant to bacteria, and consequently very few feather-degrading bacteria were found in these ornamental feathers compared to the apical part, the most exposed one; however, in non-ornamental feathers of both sexes, feather-degrading bacteria were equally found in both basal and apical feather parts.

All bird species have a gland located dorsally at the base of the tail that produces a sebaceous secretion with antimicrobial activity. Birds take this secretion with the bill and spread it on feathers to protect them against microbial pathogens. We found that those starlings with larger glands produce more secretion, and this secretion has moreover more capacity to inhibit bacterial growth; in addition, they had lower bacterial load in their feathers, and feathers were thus less degraded. Therefore females, through the evaluation of degradation status of male ornamental feathers, can estimate their capacity to fight against bacteria that may damage their feathers, which indirectly reflects the quality of males to properly maintain their hygiene and their immune system capacity.

Image caption: The picture shows the ornamental feathers of the starling male. Credits: J. J. Soler.
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.

 

Oxidative costs of personality.

Kathryn E. Arnold, Katherine A. Herborn, Aileen Adam and Lucille AlexanderNovel objects presented to blue tits. Photo provided by authors.

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Animals differ in their personalities. Some individuals are bolder, more social, more exploratory and/or more aggressive than others. These ‘personality traits’ are behavioural differences between individuals, that are stable within individuals. But why do animals, including humans, show such variation in personality? It appears that different combinations of personality traits can correlate with survival or reproductive success, but scientists do not fully understand how or why. There is the suggestion that personality reflects variation in physiology, particularly how the body defends itself against free radicals. Free radicals are unstable molecules that can cause damage to the body and are produced continuously by the body as part of living. In this project we investigated the relationships between personality and free radical damage in wild blue tits. Birds were caught in a wood in Scotland over the winter and briefly brought into captivity to measure their personality traits. We recorded how good they were at exploring a novel cage. We also determined how bold or shy they were by measuring their responses to unfamiliar objects, namely colourful plastic toys (see photo). We found that blue tits that were both shy and good explorers possessed poor defences against free radical damage. Conversely birds that were bold and poor explorers had high defences against damage from free radicals. Thus, personality types differed in their defences against free radicals, and it was the combination of an individual’s personality traits that proved important. But what does this mean in the wild? Well, when food is scarce a good explorer might benefit from finding new foraging areas and avoiding starvation, even if it suffers some tissue damage because its defence mechanisms are weak. However, when food is abundant poor explorers with good defences against free radicals are predicted to live longer. Thus, the costs and benefits of having different personality traits will all depend on the environment. In nature there is no ‘perfect’ personality, because the environment is constantly changing.

Image caption: Novel objects presented to blue tits. 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.

 

More for less: sampling strategies of plant functional traits across local environmental gradients.

Carlos P. Carmona, Cristina Rota, Francisco M. Azcárate and Begoña PecoDetail of one of the sampling units, sited in a Mediterranean grassland near Madrid (Spain). Photograph by: Cristina Rota.

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Approaches based on the traits of plants (e.g. heights or leaf areas) have allowed ecologists to tackle questions regarding the changes in assembly rules of plant communities across environmental gradients or the effects of plants on ecosystem functioning. This knowledge is essential to predict the consequences of different global change scenarios, and to restore degraded ecosystems and the services they provide. One of the most critical steps in these studies is to scale-up from traits measured in individual plants to the community level, a step that is usually accomplished by calculating community indices like the average and diversity of the trait values of the species in the community. Evidently, the reliability of these indices depends on accurate measurements of the traits of the individuals that compose each sampling unit. Unfortunately, it is generally unfeasible to measure the traits of all these individuals; instead, the most common practice is to sample a reduced number of individuals of each species and average the trait values of this sample, assigning that average to all the individuals of the species. There are, however, several alternatives regarding the identity, number and location of the sampled individuals.

We performed a very intensive sampling across an environmental gradient, which allowed us to accurately estimate the 'real' values of the community indices and their changes along the gradient. Subsequently, we simulated and compared several less intensive sampling strategies that have been used in previous studies. We found that the strategy that best estimated the 'real' values was the one in which local individuals of the species (those present in each sampling unit) were used to calculate a different average trait value for each sampling unit and species (LOC). Conversely, strategies considering a single average trait value for all the sampling units in which the species is present performed much poorly, regardless of the number of individuals used to calculate the average. Although this may appear to be bad news (more work) for ecologists, we show that the accurate results yielded by the LOC strategy can be attained without increasing the total number of individuals measured across the gradient.

Image caption: Detail of one of the sampling units, sited in a Mediterranean grassland near Madrid (Spain). Photograph by: Cristina Rota.
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.

 

Young trees shape the capacity of soil microbial communities to resist and recover following drought.

David Rivest, Alain Paquette, Bill Shipley, Peter B. Reich and Christian MessierImage courtesy of Alain Paquette.

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Soil microbial communities (i.e. bacteria and fungi) are key players in soil functions such as nutrient cycling, plant productivity and climate regulation and are fundamental for the integrity of terrestrial ecosystems following disturbance. Resistant soil communities remain essentially unchanged when subject to disturbances, such as severe drought. Resilient soil communities have a high recovery capacity after disturbance. Soil microbial communities that are resistant or resilient to drought are desirable for sustainable soil use and management, as they tend to maintain soil functions. Drought may be a major threat to tree production and its occurrence and severity are predicted to increase in many regions of the world over the next several decades. Therefore, it is important to understand how soil microorganisms respond during and after severe droughts in tree communities, and the factors explaining this response, such as tree functional traits (i.e., features related to different functions such as growth or nutrition) and soil properties.

In this study, we compared soil biochemical properties and microbial response following drought in three different 4-year-old tree monocultures and two two-species combinations that were planted in a high-density tree experiment located in southern Québec (Canada). We selected different North American temperate tree species that have contrasting functional traits. We expected that differences in functional traits between tree species would be reflected in divergent soil biochemical properties, and that these differences, in turn, would drive soil microbial resistance and resilience to drought.

We showed that tree monocultures and species mixtures influenced soil chemistry, soil biological properties and microbial resistance and resilience. Both synergistic and antagonistic effects of tree mixtures on different soil properties were found. Tree monocultures surpassed species mixtures as a key driver of resistance and resilience of soil microbial communities to drought. Interestingly, soil microbial resistance was higher in tamarack than in sugar maple monocultures. Conversely, resilience was higher under sugar maple than under tamarack monocultures. We found evidence that differences in a few leaf litter traits between tree species are sufficient to rapidly alter soil nutrient availability, especially nitrogen, which can in turn have important consequences for soil microbial resistance and resilience to drought.

Image caption: Image courtesy of Alain Paquette.
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.

 

Sleeping single in a double bed: for tropical hibernators sociality is a hurdle rather than advantage.

Kathrin H. Dausmann & Julian GlosTHE MALAGASY PRIMATE CHEIROGALEUS MEDIUS FACE-TO-FACE WITH THE REPTILE URUPLATUS HENKELI, WITH WHOM IT SHARES BODY TEMPERATURE PROFILES DURING HIBERNATION.

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Doesn’t it sound nice to cuddle close to a fellow conspecific when it is cool and unfriendly outside? The Malagasy fat-tailed dwarf lemur (Cheirogaleus medius) does not think so. This small primate is usually a very social creature, living in tight family groups where pairs only separate when one partner dies. However, this changes when winter approaches. Madagascar is a large, tropical island off the east coast of Africa and home to – and famous for – 103 species of lemurs, the highest percentage of indigenous primates anywhere on earth. It might not be the kind of place one would expect to find hibernating mammals, let alone primates. Yet, this is just what the small-bodied dwarf lemurs do. They resort to the same strategy used by marmots, ground squirrels and dormice to survive the cold northern winters – spending at least seven months of the year hibernating through harsh times brought on by seasonal drought during the Malagasy winter. As its name suggests, most of the energy used to fuel life during hibernation in the fat-tailed dwarf lemur is stored in the tail, and it fattens up to almost double its body mass before the hibernation season. Usually, mammals profit from huddling in groups because this reduces heat loss during cool conditions, and thus decreases the need to activate internal heat production, helping them save energy. However, in the fat-tailed dwarf lemur body temperature during hibernation changes passively with external conditions in a reptile-like fashion, instead of being maintained internally. Depending on the insulation of the tree hollow used for hibernation, this can result in a daily fluctuation in body temperature of up to 20 degrees Celsius. In this practice, the dwarf lemurs prefer not to be bothered by their dear family, because in larger groups unwelcome interruptions can make the hibernation state less energy-efficient. Therefore, hibernating alone helps dwarf-lemurs to conserve their precious fat resources and thus enhance their chance of survival, leaving them in better body condition for the next reproductive period after reuniting with their mate at the end of the winter.

Image caption: The Malagasy primate Cheirogaleus medius face-to-face with the reptile Uruplatus henkeli, with whom it shares body temperature profiles during hibernation.
This paper can be found online in its As Accepted form (not typeset or proofed) here.

 

Root responses of grassland species to spatial differences in soil history.

Marloes Hendriks, Eric J.W. Visser, Isabella G.S. Visschers, Bart H.J. Aarts, Hannie de Caluwe, Annemiek E. Smit-Tiekstra, Wim H. van der Putten, Hans de Kroon & Liesje MommerLeucanthemum vulgare growing in homogeneous (Ho) and heterogeneous (He) distributions of soil biota. Photo credit: Isabella G.S. Visschers.

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Plants live in environments in which local conditions differ, for example the amount and type of available nutrients. If the availability of nutrients is patchy, plants can direct their roots towards patches that have highest availability. Similar patchy distributions can be found for soil biota (e.g. fungi or bacteria), but the response of plants to this type of spatial variation is not known.

Here, we investigated if rooting patterns of plants can respond to the patchiness of soil biota. We expected that plants might avoid patches with pathogenic soil biota. To test our expectation, we used four grassland species and soils on which they had been growing before, to obtain ‘own’ and ‘foreign’ soils. We created four compartments in a pot and assigned soil of each of the four species to one of the compartments (heterogeneous soil treatment). As a control situation we mixed the four soil types (homogeneous soil treatment) and in another control we removed soil biota. In order to study effects of soil biota on nutrient uptake by roots we added labelled nitrogen (15N) to the soil.

We found that most species performed better when their own and foreign soils were distributed heterogeneously, rather than when they were homogeneously mixed. The amount of roots and the nitrogen uptake rate of these roots were higher in ‘foreign’ than ‘own’ soils. When we sterilized the soil to remove soil biota, these differences disappeared, showing that indeed the soil biota caused the difference between heterogeneous and homogeneous soils.

We conclude that plants perform better if they grow in soils with patchy distribution of pathogenic soil biota, compared to when the same amount of pathogens are homogeneously mixed, because plants can selectively avoid the patches with pathogens. Plants can be disproportionately efficient in nutrient acquisition in patches without soil biota. Our results imply that diverse plant communities may be more productive than species poor vegetation, because in species rich vegetation plant species can find more patches without soil pathogens where they could maximize nutrient acquisition.

Image caption: Leucanthemum vulgare growing in homogeneous (Ho) and heterogeneous (He) distributions of soil biota. Photo credit: Isabella G.S. Visschers.
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.

 

Grasshopper effect traits reflect their feeding niche and determine their impact on plant community biomass.

Hélène Deraison, Isabelle Badenhausser, Luca Börger & Nicolas GrossFemale grasshopper (Chorthippus_biguttulus). Photo provided by authors.

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Herbivorous arthropods, such as insects, may play an important role in regulating plant diversity and ecosystem functioning (e.g. nitrogen cycling). But it is unclear which mechanisms drive plant – arthropod interactions and ultimately arthropod effects on plant communities. Various herbivore characteristics (i.e. what we called here functional traits) have been assumed to determine herbivore impact on plant communities. For instance, herbivore body size has been proposed as a key trait determining the quantity of biomass consumed. But its effect might be modulated by herbivore food preferences (i.e. herbivore feeding niche). In this case, herbivore chemical traits (e.g. carbon:nitrogen ratio) or biomechanical traits (e.g. mandibular traits; biting strength) have been hypothesised to be related to herbivore feeding niche. Yet, how functionally contrasted herbivores may impact plant community biomass in real field conditions, and what is the relative importance of different herbivore traits, has never been experimentally tested.

We set up a cage experiment in a species-rich grassland and tested how grasshopper traits may explain their effect on plant biomass. Six grasshopper species were selected because they show contrasted traits and feeding niches.

Grasshopper impact ranged from 0% up to 60% depending on the species considered. By comparing the relative importance of multiple interacting grasshopper traits, biting strength appeared to be a key trait determining grasshopper feeding niche and impact on plant biomass. Importantly, we demonstrated that only two simple plant traits (C:N ratio and leaf dry matter content) well predicted grasshopper feeding niche. For instance, herbivores with strong mandibular strength preferentially chose tough leaves while herbivores with weak mandibular strength selected opposite plant attributes.

Our study provides a first experimental test of the relationship between herbivore traits and their niche, which in turn determines their impact on plant community biomass and ultimately on ecosystem functioning. It also contributes to the development of a trait-based approach in a multitrophic perspective and shows that simple traits can predict the intensity of trophic linkages and herbivore effects at the level of the entire plant community.

Image caption: Female grasshopper (Chorthippus_biguttulus). 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.

 

To survive against cannibalism: growth and developmental acceleration in pre-feeding salamander hatchlings in the presence of the conspecific hatchlings.

Osamu Kishida, Ayumi Tezuka, Akiko Ikeda, Kunio Takatsu & Hirofumi MichimaeVentral aspect of 7-days-old Hynobius retardatus salamander hatchlings reared alone (left) and with conspecifics (right).  Photo by Osamu Kishida.

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In many fish and amphibian species, vast numbers of embryos may hatch at the same time. In such situations, the hatchlings can be exposed to intensive cannibalistic interactions from conspecifics (members of the same species). How do hatchlings spend this vulnerable life stage?

Cannibalism success of the Japanese Ezo or Hokkaido salamander species (Hynobius retardatus) is highly dependent on the balance between the gape width of the cannibal (how wide it can open its mouth) and the head width of its prey, so fast growth in the pre-feeding stage is expected to contribute strongly to the survivorship of the salamander hatchlings in conspecific interactions. In this study, we report experimental evidence showing adaptive acceleration of growth and development in the pre-feeding hatchling stage. Ezo salamander hatchlings reared with conspecifics became larger and developed faster than those reared alone, the time to the start of feeding was shorter, and the burst swimming speed for hatchlings reared with conspecifics was faster.

Our predation trials revealed the advantages of growth and developmental acceleration in cannibalistic interactions. The hatchlings reared with conspecifics were more successful at cannibalizing small hatchlings and were also highly resistant to being cannibalized themselves by large conspecifics, compared to hatchlings reared alone. Because salamander larvae that cannibalize other individuals in their early developmental period exhibit rapid growth and metamorphose early with larger size, growth and developmental accelerations are likely key mechanisms for their life history success.

Image caption: Ventral aspect of 7-days-old Hynobius retardatus salamander hatchlings reared alone (left) and with conspecifics (right). Photo by Osamu Kishida.
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.

 

Sex-specific differences in ecomorphological relationships in lizards of the genus Gallotia.

Marta Lopez-Darias, Bieke Vanhooydonck, Raphael Cornette and Anthony HerrelGallotia on Isoplexis.                   Photograph by Beneharo Rodríguez

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Males and females often differ from one another in ways that reflect different investment in features relevant to the fitness of each sex. Whereas females typically invest in traits related to producing offspring, males tend to invest more in features related to territory defense or male-male combat. However, how differences in morphology between the sexes affect performance traits that are important in the ecological context of an animal, such as the ability to escape predators or to eat certain food types, remains poorly understood. Here, we test whether head morphology, the ability to bite hard, and diet are similar in male and female lizards (Gallotia) from the Canary Islands. These lizards are known for their sexual dimorphism suggesting that the relationships between form and function may also differ between the sexes. We collected data on bite force and head morphology and shape for both sexes of all seven known living species on all seven islands of the archipelago. Moreover we collected diet data for five out of the seven species. Our results show that the evolution of head morphology is associated with the evolution of the ability to bite hard in both sexes. However, only in females was the ability to bite hard associated with the evolution of diet, with females with higher bite forces including larger amounts of plant matter in their diet. In males, on the other hand, head morphology and bite force are not related to diet. Moreover, males with high bite forces have a wide snout suggesting that head shape and bite force may be evolving principally in relation to male-male combat in males. Our data thus suggest that head morphology and associated functional traits such as biting may evolve differently in males and females.

 Image caption: Gallotia on Isoplexis. Photograph by  Beneharo Rodríguez, website: www.gohnic.org
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 lizards evolved a fossorial syndrome within the Brazilian Caatingas.

Agustín Camacho, Rodrigo Pavão, Camila Nascimento Moreira, Ana Carolina B.C. Fonseca Pinto , Carlos Navas & Miguel Trefaut Rodrigues Photo provided by authors.

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Among the reptile order Squamata (lizards and snakes), the loss of limbs to give a snake-like morphology is likely the most dramatic evolutionary change that has occurred. It is often associated with the acquisition of an underground, burrowing life-style, nocturnality and a preference for relatively low temperatures. Nonetheless, how such an interesting evolutionary transition took place remains poorly understood. We examined this process in ten, closely-related species of gymnophthalmid lizards (spectacled lizards) from the Brazilian Caatinga (desert scrubland), representing one full transition from typical lizard species to burrowing snake-like ones. Some of the species studied have typical lizard morphology, while others have a burrowing, snake-like morphology. Species of both forms live together in sandy soil regions of the Brazilian Caatingas and burrow to some extent. We used automatic temperature data loggers and X-ray images to study evolutionary relationships between morphology, burrowing performance, exposure to extreme temperatures and the evolution of thermal physiology in those lizards. Our results show that the evolution of a snake-like morphology allows a better burrowing performance in our studied species. An improved burrowing performance allows those species to reach thermally safe (cooler) areas and also seems to favour the evolution of lower preferred temperatures. At our study sites, snake-like lizards not only can avoid diurnal extreme temperatures at the soil’s surface, but also access their preferred temperatures within the sand until late night. In addition, we found that snake-like lizards active at cool hours of the day have lower critical thermal limits. Using the obtained evidence, we propose a sequential explanation for the evolution of the snake-like, burrowing syndrome in lizards that can be tested in other lineages.

Image caption: 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.

 

Dependence of diverse consumers on detritus in a tropical rainforest food web as revealed by radiocarbon analysis.

Fujio Hyodo, Takashi Matsumoto, Yoko Takematsu and Takao Itioka Aerial view of a tropical rainforest, Lambir Hills National park, Sarawak, Malaysia. Photo by Fujio Hyodo.

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Food webs represent trophic relationships among various consumer organisms, i.e. who eats what. They are often classified into two types: plant-based food webs, starting with living plants as basal resources, and detritus-based food webs, which begin with dead organic matter (detritus). Although the two food webs have been studied separately, recent studies suggest that the coupling of the two food webs by generalist predators plays an important role in terrestrial ecosystem functioning and stability. For example, increased input of detritus could increase the abundance of generalist predators, which would lead to control of herbivory. Despite the importance of the energy and material flows from belowground, however, it remains unclear how commonly generalist predators depend on detritivores, particularly in terrestrial ecosystems.

We estimated ‘diet ages’ of diverse consumers in a tropical rainforest by measuring their radiocarbon concentration. ‘Diet age’ is the lag time between primary production and its utilisation by consumers. Radiocarbon increased after atmospheric nuclear bomb testing during the cold war and has been decreasing through mixing with ocean and biosphere since the early 1960’s, so the known level of atmospheric radio carbon can be used to estimate diet age. Our results show that herbivores, such as butterflies and bees, had diet ages 0–1 year, whereas detritivores, such as termites, had older ages of 6–>50 years. Generalist predators, such as army ants and treeshrews, had intermediate ages of 2–8 years. Given the known feeding habits of generalist predators, these intermediate ages indicate that generalist predators couple the energy and material flows from plant-based and detritus-based food webs. Further, our results demonstrate the time frame in which energy and materials flows occur through a tropical rainforest food web. Knowing this time frame would be helpful for the conservation and management of ecosystems.

Image caption: Aerial view of a tropical rainforest, Lambir Hills National park, Sarawak, Malaysia. Photo by Fujio Hyodo.
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.

 

Inbred Host Plants Promote Enhanced Insect Growth and Flight Capacity.

Scott L. Portman, Rupesh R. Kariyat, Michelle A. Johnston, Andrew G. Stephenson & James H. Marden Manduca adult.

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Insects use flight to evade predators, locate mates, and colonize new habitat; thus, improved flight capability has the potential to increase an adult insect’s survival, reproductive success, and geographic distribution. Plant tissues, consumed by larvae (caterpillars), will later provide nutrients the adult insects ultimately need to develop their flight muscles. Most studies investigating the influence of host plants on insect herbivores only look at effects on caterpillars. However, this approach overlooks nutritional effects on the adults and the important contributions the adults make to the size and distribution of the insect’s population. Here we examine how differences in the quality of horsenettle (Solanum carolinense) host plants affect flight muscle development and flight muscle function of one of its natural herbivores, tobacco hornworm moths (Manduca sexta).

We used inbreeding as a mechanism to produce variation in host plant quality. Inbreeding in horsenettle is known to reduce the plant’s ability to defend itself against herbivores and pathogens. In both field and laboratory conditions, tobacco hornworm caterpillars prefer to feed on inbred plants compared to outbred plants, suggesting fitness advantages from eating weakly defended inbred plants as opposed to better defended outbred plants. We found caterpillars that ate inbred plants grew faster and developed into larger pupae (chrysalises) compared to caterpillars that ate outbred plants. Growth differences in the caterpillars also impacted the adult stage (moth) of the insect. In free-flight tests, moths that fed on inbred plants as caterpillars exhibited improved flight muscle metabolic function. Moreover, we found molecular evidence showing higher muscle metabolic outputs correlated with changes to the amino acid composition of a key regulatory protein in their flight muscles.

Our results show that host plant inbreeding can create effects that cascade through larval and pupal development to affect flight muscle function of the adult stage. Hence, host plant inbreeding can influence important life history traits of insect herbivores, such as mating success, survival, and dispersal. Broadly, our findings reveal that changes to the genetics of a population at one trophic level can affect the development and physiology of an animal at a higher trophic level.

Image caption: Manduca adult.
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.

 

Age-related deterioration in duckweed.

Patrick M. Barks & Robert A. LairdA deceased frond of duckweed and her last-produced offspring. Photograph by Patrick Barks..

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As they grow old, many organisms experience progressive bodily deterioration resulting in declining rates of survival and reproduction – a phenomenon known as ageing or senescence. From an evolutionary perspective, ageing seems inherently detrimental to fitness and yet it occurs in most species across the tree of life. Thus, ageing has long been considered something of an evolutionary paradox – it is maladaptive and yet still common.

Modern evolutionary theories of ageing have addressed this apparent paradox but still fall short of explaining the wide variation in rates and patterns of ageing that exists in nature. One potential shortcoming of modern theories of ageing is that they implicitly assume ageing can only manifest through declining rates of survival and reproduction, but not through age-related declines in the fitness of one’s offspring. If age-related declines in offspring fitness occur in nature, than our theories of ageing may need to be updated accordingly.

Previous research suggests parental-age-related declines in various offspring traits occur in many organisms, from ladybugs to aquatic plants to humans. For example, in the aquatic plant duckweed, older parents produce smaller offspring with shorter lifespans than younger parents. Size and lifespan, however, are poor measures of fitness, and so for most species, we simply do not know whether offspring fitness declines with increasing parental age.

To resolve this issue, we measured age-related changes in three important demographic rates (survival, reproduction, and offspring fitness) in common duckweed, a small aquatic plant. We isolated hundreds of plants individually in Petri dishes filled with a liquid growth medium, and observed them daily for survival and reproduction. The offspring of a subset of these plants were transferred to their own Petri dishes so that we could measure their fitness (the rate of increase in their descendants) and relate that back to the age of their parents.

We observed strong age-related declines in survival, reproduction, and importantly, offspring fitness. Thus, we suggest evolutionary theories of ageing should be updated to consider the effect of declining offspring fitness. These updated theories may help us better understand the variation in patterns of ageing observed in nature.

Image caption: A deceased frond of duckweed and her last-produced offspring. Photograph by Patrick Barks.
This paper can be found online in its As Accepted form (not typeset or proofed) here.

 

Is tropical montane forest heterogeneity promoted by a resource-driven feedback cycle?

Florian A. Werner and Jürgen HomeierContrasting forest types at the study site in the Andes of Ecuador: stunted, open ridge-crest forest (top) and tall lower slope forest near creek (bottom). These two adjacent forest types share only few tree species. Photos: Florian Werner.

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Separated by only few dozens of meters, ridge crests of tropical mountains often differ strikingly from neighbouring valleys in terms of structure and species composition of their forests. These contrasts are not well understood despite their importance for the maintenance of biodiversity and provision of ecosystem services such as carbon storage.

We studied tree biomass and productivity (tree growth, production of leaves), quality of fresh leaves and leaf litter (nutrient concentrations and phenolics, an important group of chemicals produced by plants to deter plant-feeding animals), levels of leaf herbivory (% leaf area loss due to animal-feeding) and decomposition of leaf litter (freshly fallen leaves) in upper (near ridge crests) and lower slope position (near creeks) in a montane forest in Ecuador.

We found that forest canopy height, production of wood and foliage, quality of fresh leaves and leaf litter, and leaf losses due to herbivory, were significantly lower on upper slopes. Likewise, soil nutrients were lower on upper slopes, where we found decaying leaf litter accumulated in thick humus layers instead of decomposing readily as on lower slopes. As shown by a decomposition experiment, leaf litter from upper slope forest decomposed more slowly than litter from lower slope forest no matter which of the forest types it was placed in.

Our results suggest that the differences we observed between slope positions ultimately result from a pronounced scarcity in plant nutrients in upper slope forest that is likely to arise from nutrient losses through down-slope fluxes. The size of the contrast between these vegetation types, however, suggests that nutrient poverty near ridges is exacerbated by a positive (self-enforcing) feedback cycle in which nutrient-poor soil favour plants that produce leaves with low nutritional value and high concentrations of phenolics to deter leaf-eating animals, since the nutrients lost in eaten leaves are very difficult to replace. Because these leaf characteristics also deter organisms that decompose leaf litter, nutrients remain locked in accumulating humus instead of being liberated by decomposition and made available to plants again. Consequently, the nutrients available to plants decline even further, favouring plants producing foliage that is ever more difficult to decompose.

Image caption: Contrasting forest types at the study site in the Andes of Ecuador: stunted, open ridge-crest forest (top) and tall lower slope forest near creek (bottom). These two adjacent forest types share only few tree species. Photos: Florian Werner.
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.

 

Survival of the fattest? Not in the brown anole.

Robert M. Cox and Ryan CalsbeekA female brown anole, Anolis sagrei. Illustration by Amy Y. Zhang.

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Darwinian natural selection is often described as the “survival of the fittest”. However, determining which individuals are actually the fittest can be challenging, so biologists often use proxies in place of fitness. One popular proxy is body condition: the mass of an animal relative to its size or length. “Fatter” animals exhibiting higher body condition are assumed to be in a better energetic state, which is predicted to improve their chances of survival and reproduction. But is “fatter” really “fitter” in nature? By analyzing a decade of survival records for over 4600 individual brown anole lizards across seven populations in The Bahamas, we show that fatter is not fitter, at least when it comes to survival. Nor does natural selection tend to favor animals of intermediate condition, as might be expected if both skinny and obese lizards struggle to survive. Instead, natural selection favors large body size, at least in males. In fact, the only time that “fatter is fitter” seems to hold true is for the largest males in the population, who experience an extra boost in their probability of survival if they are also in high condition.

Image caption: A female brown anole, Anolis sagrei. Illustration by Amy Y. Zhang.
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 place to hide: how nooks and crannies help species survive in new environments.

Daniel Barrios-O’Neill , Jaimie T. A. Dick , Mark C. Emmerson , Anthony Ricciardi and Hugh J. MacIsaacPhoto credit: Daniel Barrios-O'Neill .

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These days, we humans find ourselves at the top of the food chain more often than not. Still, it’s interesting to reflect on what the world is like for the vast majority of the smaller inhabitants of the planet. For all but a few, danger abounds, and avoiding being eaten is a regular feature on the daily ‘to do’ list.

Ecologists have long observed that the structural complexity of the places animals inhabit —trees, rocks, reefs and almost anything which is physically something — is fundamentally important for the long term survival of small creatures, especially those attempting to avoid hungry predators. Although the reasons for this seem simple enough, the situation is often complicated, because while some aspects of structure can serve as obvious protection for prey, others can cause problems. For instance, while a single tree might provide camouflage and spaces too small for predators to access, it could also limit options for escape. And whilst the surface of a tree may appear smooth to a chimpanzee, to an ant it is a veritable maze of ravines.

In this study we approached the issue by focusing on a single component of structure, the availability of spaces too small for predators to access — the nooks and crannies. Our aim was to understand how small changes in the availability of nooks and crannies could influence the survival of prey. We used a successful invader of rivers and lakes in the British Isles, the Ponto-Caspian shrimp Chelicorophium curvispinum, as a prey and two larger shrimp species as predators. Our outcomes demonstrate that very small increases in available nooks and crannies can substantially increase the survival of the prey, and that the most telling positive effects on survival occur when prey are few in number. Increased survival at low numbers may allow prey to avoid localised extinction, and to colonise new areas.

These findings not only help to us understand how environmental architecture mediates the spread of invasive species, but also why the underside of that rock in your garden is crawling with creatures.

Image caption: Photo credit: Daniel Barrios-O'Neill.
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.

 

Basal Metabolic Rate in Tropical Birds: The Influence of Latitude and Altitude on the "Pace of Life".

Gustavo A. Londoño, Mark A. Chappell, María del Rosario Castañed, Jill E. Jankowski, and Scott K. Robinson Overview of the Manu Gradient, photo taken from the field site at 3000 m elevation with the lowland site in the background.

For decades scientists have acknowledged latitudinal and altitudinal differences in bird life history (number and size of eggs laid, nesting behaviors, and lifespan). For example, tropical birds are thought to have a slower ‘pace of life’ – they lay fewer eggs (usually two) and generally live longer than temperate birds. These differences could result from the large variation observed among latitudes and altitudes in abiotic (e.g., temperature, rainfall) and biotic (e.g., nest predation, competition) conditions. Higher latitudes and altitudes tend to be colder with more variable temperatures, whereas low latitudes and altitudes have warmer and more stable temperatures. Biotic pressures, such as nest predation, competition and parasites, tend to be higher at low latitudes and altitudes.

Our study provides data on a basic life history trait, Basal Metabolic Rate (BMR), loosely defined as the energy expended by an animal at rest, for ~250 Peruvian bird species along a 2600-m tropical altitude gradient. We also compare our BMR data from birds in Peru with BMR data collected from > 500 bird species from other studies across temperate and tropical latitudes. We use this dataset to ask the following questions. Do substantial differences in native altitude—and hence environmental temperature—influence the BMR of tropical forest birds? Is the low BMR found in other lowland tropical birds also characteristic of the geographically distant tropical birds in Peru? Do tropical birds have lower BMR than those of temperate birds? Does BMR differ among different groups of bird species (songbirds and others)?

We found that BMR does not vary among tropical altitudes or regions, but does vary among tropical and temperate latitudes and avian orders, such that birds breeding in temperate regions and songbirds have higher BMR. Our study confirms previous reports of differences in BMR between temperate and tropical bird species, consistent with the concept of tropical birds having a slower ‘pace of life’. We found no effect of environmental temperature on BMR in Peruvian forest birds across a 2600-m altitude transect (a 12 °C temperature change), reinforcing the view that low BMR in tropical birds is mainly driven by slow life history.

Image caption: Overview of the Manu Gradient, photo taken from the field site at 3000 m elevation with the lowland site in the background.
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.

 

When it comes to water, snake foetuses have priority over mom.

Andréaz Dupoué, François Brischoux, Frédéric Angelier, Dale F. DeNardo, Christian D. Wright and Olivier LourdaisUltrasonographic picture of a developing embryo (Vipera aspis).

Conflicts between a parent and offspring are not unique to humans and may occur in nature whenever there is a limited resource that the two must share. Typically, energy has been the focus of such conflicts, but water is another vital resource that has yet to be considered in the framework of parent-offspring trade-offs or conflicts. In many dry environments, water can be quite limited during certain seasons and such times often coincide with pregnancy. However, physiological demands of pregnancy mean females require a greater amount of water during this period compared to times when the female is not pregnant. Since female snakes supply energy to their developing offspring in the form of yolk that is allocated prior to fertilization, using snakes as study organisms enabled us to examine possible intergenerational water conflicts independent of energy conflicts.

We explored the trade-off over water resources between a mother and her developing embryos in a live-bearing snake, the aspic viper. We manipulated water availability (control vs. water-deprived for 20 days) to pregnant and non-reproductive female snakes. Snakes can tolerate considerable levels of dehydration and thus our treatment was ecologically relevant and non-threatening to the general health of the snakes. We examined the effects of water deprivation on female water balance, water transfer to the embryos, and reproductive performance.

Water deprivation resulted in significant female dehydration, with more pronounced effects in pregnant compared to non-reproductive females. The impacts of water deprivation on water balance were correlated with the number of offspring, with the most fecund females being more dehydrated. In contrast, water deprivation had no effect on water transfer to the offspring or on reproductive performance. Our results demonstrate that, when water is unavailable, female water balance is compromised in favour of the developing embryos, highlighting a significant trade-off over water resource between a mother and her offspring. Whether the prioritization of the offspring is a result of a “generous” mother preferentially allocating resources to her offspring or the offspring “selfishly” taking the water from the mother remains unknown. Regardless, this work demonstrates that parent-offspring conflict over water may be a substantial hurdle during the evolution of the live-bearing reproductive mode.

Image caption: Ultrasonographic picture of a developing embryo (Vipera aspis).
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.

 

Silicon concentration and population dynamics of voles.

Monika Wieczorek, Karol Zub, Paulina A. Szafrańsk, Aneta Książe and Marek KonarzewskiRoot vole, Microtus oeconomus. Photo courtesy of  K. Zub.

Population cycles of small rodents have puzzled researchers since the advent of ecological studies. One of the hypotheses is that time-delayed plant-herbivore interactions could be responsible for generating population fluctuations. Under this scenario, past overgrazing induces plants to accumulate toxic, or hard to digest, components that negatively affect growth and survival of herbivores, and thus induces cycling of their populations. Induced mechanical defences that reduce plant digestibility could be essential in deterring herbivory in grasses, which are the primary diet component of numerous herbivores that show population cycles.

Most tests of the plant-herbivore hypothesis have focused on broad categories of chemical defences, with much less attention given to mechanical defences, such as abrasive silicon (Si), which reduce palatability and digestibility of plant tissues. In contrast, many studies considered accumulation of Si by plants as a process primarily controlled by geo-hydrological factors. Therefore, we investigated the relationship between concentration of Si in fibrous tussock sedge and the population density of a major sedge consumer, the root vole, in field enclosures located in the Biebrza river valley (NE Poland) under a variety of natural water regimes and weather conditions.

We found that a high density of voles resulted in the immediate accumulation of Si by rhizomes, followed by accumulation of Si in leaves with a one-year lag time. The level of river flooding had an additional impact on Si concentration in rhizomes but did not affect silicification of leaves. Overwinter changes in concentration of Si in sedges were also influenced by fluctuations in ambient temperature and the depth of snow cover, thus affecting the quality of winter food available for voles. Smaller voles had lower mortality during early winter than large voles, which suggests that small individuals better coped with the need to extract adequate nutrients and energy from a highly silicated diet. Our results showed that changes in Si concentration in sedges can be induced by changes in vole population density and are also additionally affected by flooding and weather conditions.

Image caption: Root vole, Microtus oeconomus. Photo courtesy of K. Zub.
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.

 

Implications of lifespan variation within a leaf cohort for evaluation of the optimal timing of leaf shedding.

Noriyuki Osada, Shimpei Oikawa, and Kaoru Kitajima Photo provided by authors.

When should a piece of equipment that is increasingly worn out and less efficient be replaced? The answer should depend on how quickly it is aging. Plants face a similar question with their leaves. Plants invest resources to produce leaves in order to obtain benefits in terms of photosynthetic production. The newest fully-expanded leaf is the most productive, with minimum wear and tear and usually created at the sunniest part of the plant crown. However, as leaves get older, they become shaded more and become less efficient in their photosynthetic productivity. When should an aging leaf be replaced? For such optimization of leaf life span (LLS), how photosynthesis declines as leaves age is a critical parameter. Many researchers have attempted to quantify this parameter, often using a method of space-for-time substitution, comparing young and old leaves at a given time. Unfortunately, this approach results in a significant underestimation of the age-related decline rate of photosynthesis, as we demonstrate with a simple simulation in our paper. Our simulation also predicts that the degree of such underestimation is greater for species that have leaf cohorts that vary a lot in LLS. This prediction is supported by an analysis of published data demonstrating that the photosynthetic capacity at the cohort mean LLS was positively correlated with the variation in LLS. This strongly suggests that the age-related decline of carbon gain may be underestimated in many previous studies that neglect within-cohort variation in LLS.

Image caption: Implications of lifespan variation within a leaf cohort for evaluation of the optimal timing of leaf shedding.
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.

 

Impacts of repeated stress events on an overwintering insect.

Katie E. Marshall and Brent J. SinclairLate-instar Choristoneura fumiferana caterpillar.  Photo courtesy of Jerald E. Dewey, USDA Forest Service, United States, downloaded from Wikimedia Commons.

Organisms live in complex worlds where environmental stresses can be more or less intense, occur for longer or shorter periods, and repeat more or less frequently. And although we know a lot about the effects of a single stress event, the effects of these more complex patterns of stress are not well understood.

We tested the impacts of each of these different aspects of stress simultaneously in the eastern spruce budworm Choristoneura fumiferana to attempt to identify which types of stress cause the largest impact on physiology and long-term fitness. We subjected overwintering spruce budworm larvae to four different low temperatures either once or multiple times, with three different periods of time between each exposure. We then measured short-term effects on physiology by looking at changes in freezing point and stores of carbohydrate and cryoprotectants (chemicals that protect the larva’s tissue from freezing damage). We also allowed a subset to leave diapause (winter dormancy) and feed, then recorded survival, development time, and adult body size.

We found that in all cases the greatest impacts were due to the number of exposures and the time of year the cold exposure occurred. While there were long-term effects of cold exposure during overwintering on survival, there was no impact on adult body size or development time. This suggests that current understanding of the way stress impacts individual organisms may be missing the effects of stress variability.

Image caption: Late-instar Choristoneura fumiferana caterpillar. Photo courtesy of Jerald E. Dewey, USDA Forest Service, United States, downloaded from Wikimedia Commons.
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.

 

Bolder lizards discard their tails to compensate for risky behavior when food is abundant.

Chi-Yun Kuo, Duncan J. Irschick and Simon P. LailvauxA male brown anole lizard displaying its colorful dewlap. Photograph by Duncan J. Irschick.

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Traits that confer benefits often have costs. A fascinating phenomenon in evolutionary ecology is that individuals can offset the costs of a beneficial trait with the function of another trait (trait compensation). The most common examples of trait compensation are those between behavioral and morphological defense mechanisms, in which individuals that are morphologically more vulnerable tend to show a higher degree of predator avoidance, and vice versa. Despite numerous reports of compensation between defensive traits, two fundamental questions have still not been fully addressed. First, whether trait compensation exists among similarly-aged individuals; and second, whether and how the relationship between compensatory traits would be influenced by the amount of food resource in the environment. Using juvenile brown anole lizards, we examined the relationship between boldness, or a willingness to take risks, and the propensity for employing tail autotomy, a costly defense trait in which a lizard voluntarily discards its tail (which gradually regrows over time), under low and high food availability. We expected bolder lizards to compensate for their higher risk-taking tendency by discarding their tails more readily. We also expected the relationship between the two traits to differ under different food availability, although the exact effect might be complex and difficult to predict a priori. Although lizards raised under low and high food availability on average did not differ in boldness or the propensity for tail autotomy, bolder lizards overall did discard their tails more readily. However, this compensatory effect was present only among individuals raised with abundant food, which suggested that trait compensation was a viable strategy only when lizards can obtain enough food to quickly regrow the lost tails. Our results showed trait compensation existed among similarly-aged individuals and served as a basis for compensatory effects observed at the population, species or higher levels. In addition, we demonstrated that food availability can influence the dynamics between compensatory traits without significantly changing the mean values of the traits per se.

Image caption: A male brown anole lizard displaying its colorful dewlap. Photograph by Duncan J. Irschick.
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.

 

Oxidative stress in breeding northern elephant seals.

Jeffrey Sharick, Jose Vazquez-Medina, Rudy Ortiz and Daniel Crocker Photo provided by authors.

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Life history theory suggests that the timing and amount of effort devoted to reproduction over an animal’s lifespan is shaped by natural selection to maximize lifetime reproduction. Central to this theory is the assumption that current reproduction reduces the ability of an organism to reproduce in the future, including negative impacts on survival. This cost may involve allocation of resources to reproduction that reduce energy available for maintenance and health. In some species, called ‘capital breeders’ these trade-offs are distinct as all of the energy used for breeding comes from body reserves stored prior to reproducing. Metabolism produces a variety of reactive oxygen species that can cause damage to biomolecules, and this ‘oxidative stress’ has been theorized to be a potential source of the survival costs associated with reproduction.. Since both high rates of metabolism and fasting are associated with oxidative stress, capital breeders might be especially subject to these costs.

We examined the potential for oxidative stress in breeding northern elephant seals. Since elephant seals forage in the ocean and breed on land, they are capital breeders. Males fast from food for over 100 days while maintaining high rates of metabolism for fighting and mating. Females fast for a month while making one of the most nutrient rich milks found in nature. We compared markers for oxidative stress in males and females at the beginning and end of breeding. We measured a pro-oxidant enzyme that makes reactive oxygen species, three important anti-oxidant enzymes, markers for oxidative damage to fats, protein and DNA, and a marker for inflammation in blood samples. We found that the pro-oxidant enzyme increased across breeding and the seals responded by increasing the levels of anti-oxidant enzymes. Despite this protective response, males showed evidence of oxidative damage to fats and DNA and showed increased levels of inflammation. Females showed evidence of oxidative damage to proteins. Our results provide evidence for oxidative stress as a cost of breeding in polygynous male elephant seals and weaker evidence in females. These data support the idea that oxidative stress may underlie survival impacts of reproduction in some species.

Image caption: 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.

 

Swimming loss and recovery in the Atlantic silverside.

Kestrel Perez & Stephan MunchAdult Atlantic silversides collected in little neck bay, Long Island, NY USA. Photo credited to Kestrel O. Perez..

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For many animal species, large body size leads to higher survival and reproductive success. Because fast growth rates enable an individual to obtain a large body size sooner, it stands to reason that fast growth should be similarly beneficial. Why then, do growth rates commonly still vary in many species? In fact, most species do not grow as fast as possible, suggesting that there must be some down-sides to rapid growth. Across a wide range of animal species, there have been many documented cases of the negative effects of fast growth. One such example is the Atlantic silverside, a common marine fish, where individuals that grow rapidly have poorer swimming ability compared to slow-growing individuals of the same size. But, how long this effect lasts is currently unknown. In this study, we determined how long it takes for a fish to recover its ability to swim following a period of fast growth. We manipulated growth rate in Atlantic silversides by providing variable amounts of food, either unlimited food for the fast growth treatment or limited food for the slow growth treatment. After two weeks of these feed rations we then fed both treatments limited rations to maintain slow growth rates. We monitored swimming ability over this period. Full recovery from the effects of earlier fast growth would be indicated if swimming ability of the fish that had previously been growing fast, but were currently growing slowly, improved and became comparable to swimming ability of the fish that had always been growing slowly. Interestingly, we found that fish that had grown rapidly early in life not only had significantly poorer swimming ability, but continued to show the effects of this early period of rapid growth. We found that fish fully recovered normal swimming ability only after 1 month of growing slowly. Most surprisingly, swimming ability actually decreased before it improved.

Image caption: Adult Atlantic silversides collected in little neck bay, Long Island, NY USA. Photo credited to Kestrel O. Perez..
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.

 

Community phylogenetics and ecosystem functioning

Clarifying the discussion of how environmental variation shapes community diversity.

Nathan J. B. Kraft, Peter B. Adler, Oscar Godoy, Emily James, Steve Fuller & Jonathan M. LevineIn the Central Valley of California, USA, small depressions in the ground can fill with rainwater in the winter, creating a vernal pool habitat. The dominant plant species (shown here in bloom) that are found in these pools can tolerate immersion in the rainwaters, while the flooded conditions exclude many of the surrounding grassland species. This process of environmental filtering, seen here at a small scale, shapes patterns of biodiversity across the planet. Credit: Nathan Kraft.

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Variation in environmental factors such as temperature, rainfall and soil chemistry have profound effects on the distribution of biodiversity across the planet. Community ecologists often use the concept of "environmental filtering" to describe situations when a species is unable to survive at a site because of the environmental conditions. However, the evidence that ecologists have used to test for environmental filtering in the past is often indirect, as it is not always sufficient to rule out other potential causes, such as competition with other species. This uncertainty is particularly problematic if we try to use results from these studies to make predictions about how global change will impact species and communities.

In this study we describe a conceptual framework to help distinguish environmental filtering from other sources of variation in community structure. Strong evidence for environmental filtering comes from showing that species have the potential to arrive at a site (as a dispersed seed or as a migrant from a nearby area, for example) but are unable to survive in the environmental conditions found there. We reviewed the ecological literature to assess how environmental filtering is typically assessed, and despite the widespread use of the concept, only 15% of published studies included this direct evidence. Most studies instead rely on patterns such as species changes in abundance or changes in physiological characteristics across an environmental gradient, patterns that can be driven by other factors.

We discuss a number of ways in which both experimental and observational studies can be improved to give a more precise accounting of the role of abiotic variation in shaping community structure. By addressing these issues, ecologists can come to a clearer understanding of the multitude of ways in which environmental variation shapes patterns of diversity across communities.

Image caption: In the Central Valley of California, USA, small depressions in the ground can fill with rainwater in the winter, creating a vernal pool habitat. The dominant plant species (shown here in bloom) that are found in these pools can tolerate immersion in the rainwaters, while the flooded conditions exclude many of the surrounding grassland species. This process of environmental filtering, seen here at a small scale, shapes patterns of biodiversity across the planet. Photo credited to Nathan Kraft.
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 uptake elements as influenced by phylogeny, soil and climate.

Zhuan Hao, Yuanwen Kuang & Ming KangPrimulina bullata growing calcareous soils (Photo credit: Ming Kang).

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Plants require a large number of chemical elements to sustain their life. Understanding factors that influence elemental composition of plants is important because it provides insight into a wide range of ecological and environmental processes. Numerous experimental studies have previously documented the influence of soil and climate on elemental composition of plants, but phylogeny is still rarely considered as a factor in determining plant elemental contents (i.e. whether closely related species have similar elemental composition, even in different environments). In this study, we measured leaf concentrations of seven elements and evaluated soil properties for 177 species of the African violet subfamily Didymocarpoideae from subtropical China, a global biodiversity hotspot. We partitioned the variation in leaf element contents into the effects of soil, climate and phylogeny. Then we tested whether closely related species tend to have similar ecological characteristics (i.e. phylogenetic signal) at two different phylogenetic scales (subfamily vs genus). We also used phylogenetic comparative methods to assess the impacts of soil and climatic conditions on leaf element concentrations.

We detected a strong phylogenetic signal in leaf elements as well as for soil and climate variables at the subfamily level, whereas the large genus Primulina exhibits no significant phylogenetic signal in leaf elements or in most soil variables. We found an influence of both soil and climatic conditions on leaf element concentrations. However, the patterns of the relationships between leaf elements and soil and climate variables vary at the subfamily and genus levels. Phylogeny has a stronger effect than soil and climatic factors on leaf element contents at the subfamily level, while leaf elements within the genus Primulina are mostly influenced by environmental conditions. We conclude that the influences of taxonomy, soil and climate on leaf element concentrations are dependent on the phylogenetic scale of analysis, highlighting the need to integrate phylogenetic scales to explore the influence of soil and climatic conditions on leaf element concentrations.

Image caption: Primulina bullata growing calcareous soils (Photo credit: Ming Kang).
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.

 

Hard work, dominance and health in a Kalahari bird.

Dominic L. Cram, Jonathan D. Blount & Andrew J. YoungFemale white-browed sparrow weaver in an Acacia tree. Credit Dominic Cram.

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When groups of animals live together (including humans), they often divide workloads, and some individuals work harder than others. Are the hardest-working individuals the healthiest, and does this allow them to work harder than everyone else? Does their work-rate impact their health, leaving the hard-workers in poor condition?

We investigated these questions in groups of white-browed sparrow weavers, in the Kalahari Desert. Although they share workloads as ‘cooperative breeders,’ within each group the dominant male and female work much harder than the subordinates. Dominants are the only birds that breed, with dominant males singing to attract their mate and dominant females producing all eggs and providing most of the care for nestlings. Both dominants also work hardest to defend the group’s territory. How do the unequal workloads of dominants and subordinates relate to their health?

We focussed on one aspect of the birds’ health: oxidative status. Previous studies have shown that hard work can increase the generation of harmful free radicals. Antioxidant defences help animals protect themselves, but if this protection is overwhelmed, oxidative stress can result. Oxidative stress is thought to be involved in many diseases and ageing.

First, we blood-sampled 93 birds before the breeding season began, to look at whether dominants (the hard-workers) had better oxidative states than subordinates, with stronger antioxidant protection and lower oxidative damage. We found that, in fact, there were no differences between dominants and subordinates in oxidative states before breeding.

Next, we sampled the same 93 birds after their long breeding season, to examine whether the dominants’ hard work during the intensive six months of breeding left them exposed to oxidative stress. After the breeding season, we found that dominant females (the hardest workers) were suffering from weakened antioxidant protection, compared to their subordinates.

Our study suggests that differences in oxidative status may not lead to differences in work-rates, but that unequal sharing of workloads in animal societies can leave the hardest-workers with poor antioxidant protection. This could leave those working hardest at higher risk of poor health, and could lead to accelerated ageing.

Image caption: Female white-browed sparrow weaver in an Acacia tree. Credit Dominic Cram.
This article can be found here.

 

Is the energy expenditure of free-living animals linked to their metabolic costs at rest?

Jorg Welcker, John R. Speakman, Kyle H. Elliott, Scott A. Hatch and Alexander S. KitayskyKittiwakes breeding at the study site on Middleton Island, Alaska, USA. Photo  by Jorg Welcker.

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Reproduction is energetically costly and the overall rate at which animals expend energy is usually highest when they rear their young. The overall rate of energy expenditure integrates the energy an animal spends to raise its offspring and to keep its own body up and running. The resting metabolic rate, on the other hand, measures the minimal energetic cost to an animal at rest to maintain its body tissues.

A widespread assumption is that an increase in parental energy expenditure requires a concurrent increase of the resting metabolic rate as higher energy intake and expenditure would need to be facilitated by larger or metabolically more active internal organs such as the heart, liver or alimentary tract. Larger or costlier metabolic machinery would, in turn, result in higher resting energetic costs. However, if changes in resting and overall energy expenditures were not inherently linked, it could be beneficial for animals to reduce their resting energetic costs as they could thus increase the amount of energy spent on raising young.

We examined whether this might be the case in free-living kittiwakes. We manipulated the energy demands of parents by increasing the number of chicks in their nests or by removing entire broods. We also manipulated energy supplies by providing some nests with supplemental food.

We found that overall and resting metabolic rates were not inherently linked: birds that raised chicks had higher overall energy expenditure yet lower resting metabolic costs compared to birds that had their broods removed. Overall energy expenditure was constrained as neither parents of enlarged broods nor those provided with unlimited food spent more energy than controls. Thus, our results suggest that reducing resting energetic costs is a strategy to increase the amount of energy allocated to raising young when overall energy expenditure is constrained. The increase in energy allocated to chick rearing caused higher levels of stress incurred by parents, suggesting that such a strategy might be costly to the parental birds.

Image caption: Kittiwakes breeding at the study site on Middleton Island, Alaska, USA. Photo by Jorg Welcker.
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.

 

Less is more: choosy wasps used in biological control show why a diverse diet is not always an asset.

Silvia Rossinelli and Sven Bacher Parasitic wasp searching for its leafminer host.

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The question of why species should specialize, i.e. use only a fraction of all resources available to them, has puzzled scientists and non-scientists alike. The proverbial saying "the Jack of all trades is master of none" provides an intuitive explanation. It implies that there should be a trade-off between the ability to use many different resources and the efficiency of using each single one. Thus, specialists should gain advantages on their resource compared to generalists. However, empirical tests so far have had problems showing such trade-offs and their importance for the evolution of specialization is still debated.

Parasitic wasps are one of the largest insect groups with maybe more than 1 million species. They parasitize other insect species by laying their eggs upon or inside the host’s body, where hatching larvae develop and eventually kill the host. For about 100 years, parasitic wasps have been widely used for the biological control of insect pests worldwide. Within this insect group all degrees of diet breadth are found, however, narrow host ranges prevail.

We analysed the history of parasitic wasps that were released to control pest insects and found that specialised wasps, i.e. those that can only parasitize a few pest species, establish better than generalist species with a wide host range. Thus, this is the most comprehensive test for the hypothesis that specialists are generally better able to use their hosts than generalists. The results provide the first robust support for the general importance of trade-offs in the evolution of specialization in the mega-diverse group of parasitic wasps. However, specialization is not always more advantageous; in environments where the preferred host is not always available, generalists will profit from being able to utilise a variety of different hosts.

Image caption: Parasitic wasp searching for its leafminer host.
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.

 

Food jumpstarts feather moult.

Raymond M. Danner, Russell S. Greenberg, Julie E. Danner and Jeffrey R. WaltersA swamp sparrow moulting throat, face, and crown feathers in eastern North Carolina.  Photo by Jeff Lewis, used with permission.

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Moulting (periodic loss of old feathers and growth of new ones) is critical for many bird species, but it costs both time and energy. Moulting may interfere with other important activities, such as breeding, migration, and maintaining body heat. Therefore, the timing of moult is essential for ensuring a successful year. In birds, the prebreeding moult is especially important because it may delay breeding. The prebreeding moult is also when males of many species acquire colourful plumage that is important for attracting mates and competing with other males.

The end of the winter is a lean time for many birds because food resources have been depleted since the previous fall. We hypothesized that the scarcity of food in late winter inhibits the initiation of prebreeding moult. We experimentally tested, for the first time, if food abundance influences the timing of moult in the wild. We conducted a controlled food supplementation experiment on free-living swamp sparrows (Melospiza georgiana) preceding and during the time of natural prebreeding moult (January–March 2009, 2010).

Supplemented birds began moulting the body, face, and crown earlier than control birds (11, 14, and 8 days earlier, respectively) indicating that food abundance limits the initiation of moult. Along with interannual variation in moult timing, these results indicate that day length is not the sole cue for moult initiation. Both control and supplemented birds moulted in sequence, starting with the body, followed by the crown 9 days later, and the face 11 days later. The presence of a sequence further suggests energetic limitation of moult or possibly a strategy to moult specific regions first to ensure completion at an optimal time.

This study provides novel experimental evidence that food abundance can limit moult timing in the wild. Food limitation of moult timing could affect the timing of breeding or feather quality, and thus cascade through other life history stages in the annual cycle and ultimately affect reproductive success. These results indicate that food availability is a cue for moult initiation, possibly acting secondarily to photostimulation.

Image caption: A swamp sparrow moulting throat, face, and crown feathers in eastern North Carolina. Photo by Jeff Lewis, used with permission.
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.

 

Ageing gracefully: physiology but not behaviour changes with age in a diving bird.

Kyle H. Elliott, James F. Hare, Maryline Le Vaillant, Anthony J. Gaston, Yan Ropert-Coudert and W. Gary AndersonMurres in flight. Photo provided by authors.

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How can long-lived wild birds both work hard and live long? We examined this question by studying murres (also known as guillemots) aged 3-30 years. Murres have the highest flight costs, for their body size, of any flying animal. They dive exceptionally deep for their body size (over 150 m for five minutes). Yet they also have exceptionally long lives for their body size; they live decades longer than rabbits, which weigh roughly the same. To examine how metabolism changes with age in wild murres, and how that affects dive performance, we measured oxygen consumption, oxygen stores and dive behaviour. Both oxygen stores and oxygen consumption rate declined with age, which we suggest reduces the effect of high metabolism on ageing. In contrast, there was no change in dive performance with age; old murres dove as deep, for as long and spent as much time recovering at the surface as young murres. Thus, multiple physiological systems changed in tandem with advancing age in murres, and offset each other such that there was no detectable decline in behavioural performance. Murres were able to maintain their ‘healthspan’ into old age.

Image caption: Murres in flight. 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.

 

Maternal effects influence phenotypes and survival during early life stages in an aquatic turtle.

Timothy S. Mitchell, Jessica A. Maciel and Fredric J. JanzenA hatchling painted turtle emerges from the nest after winter.

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Many egg-laying animals do not care for their young, but this does not mean that good mothering is not important for offspring. For such animals, there are two maternal effects that are particularly important: nest-site choice and egg size.

We explored the importance of such maternal effects in the painted turtle (Chrysemys picta). By selecting particular microhabitats at the time of nesting, the mother turtle can partially influence the abiotic conditions her eggs will experience during incubation and the hatchlings will experience as they overwinter within the natal nest. This abiotic environment is very important for two reasons: it can shape phenotypes of developing offspring via phenotypic plasticity, and it can act as a selective force. In this field experiment, we compared offspring incubating and hibernating in maternally-selected nests to those in randomly-selected nests. Our results show that mothers selected nests that were relatively open (unshaded), and this resulted in maternal nests being significantly warmer than random nests during incubation. Hatchlings from these maternal nests were longer and developed faster than their counterparts in random nests. However, the ability to modify thermal environments of the nest faded during the overwinter stage. There was a weak correlation between vegetation cover and nest temperature, and maternal and random nests experienced similar thermal environments.

We also tracked individual eggs and hatchlings, and showed that larger eggs produce larger hatchlings. These larger hatchlings had a higher probability of surviving winter, where experiencing lethally cold temperatures was a substantial source of mortality. This novel result provides further support for the “bigger-is-better” hypothesis in early life stages of freshwater turtles.

In the turtle world, three clichés ring true: mother knows best, size matters and location is everything (or at least, it is very important).

Image caption: A hatchling painted turtle emerges from the nest after winter.
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.

 

Do eggshells act like sunscreen?

Golo Maurer, Ivan Mikšík, Steven J Portugal, Mark E Hauber, Douglas Russell, Phillip CasseySong thrush eggs. Photo provided by authors..

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The eggs of birds have an amazing array of adaptations to ensure the safety of the embryo developing inside. Such adaptations can include camouflage of the shell to help protect against predation, special pores that allow the correct amount of air into the egg and infection-fighting pigments to help the embryo fight disease. One important aspect the shell of the egg must control is the amount of light that penetrates through to reach the embryo. Too much light penetrating the eggshell will result in lethal levels of radiation from the UV light, but too little light can cause embryo deformities and increase the likelihood of disease. Therefore, the eggshell has to ensure that just the right amount of light is allowed through the shell. Birds nest in a wide range of environments and habitats, including extreme temperatures, altitudes, in burrows, on cliffs; how does the egg of each species in differing environments make sure the right amount of light reaches the embryo? We examined how the eggshells of British breeding birds have adapted to different environments, and how different shells control the amount of light that reaches the embryo. We found that the eggs of species that nest in burrows, holes and other closed environments let more total light pass through the eggshell, compared with species that nest in the open. Specifically, we show that less light passes through thicker eggshells with greater total pigment concentrations. The pigment potentially acts like sun-block. It seems, therefore, that greater light transmission through the shell is required to assist embryonic development under low-light exposure. To make sure enough light gets through to the embryo in these dimly-lit conditions, eggs of birds that nest in burrows and holes are white, allowing more light in as there is less pigment to block the sun. For birds who have a long incubation period (exposing their eggs to the sun for longer), their eggs are often dark with pigment, letting significantly less of the potentially harmful, ultraviolet (UV) light pass through the eggshell.

Image caption: Song thrush eggs. Photo provided by authors..
This paper can be found online in its As Accepted form (not typeset or proofed) here.

 

Daily energy expenditure during lactation is strongly selected in a free-living mammal.

Quinn E. Fletcher, John R. Speakman, Stan Boutin, Jeffrey E. Lane, Andrew G. McAdam, Jamieson C. Gorrell, David W. Coltman and Murray M. Humphries Female red squirrel with one of her pups outside of her grass nest. (Photo credit: Ryan W. Taylor).

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Energy is a currency of life because all animals must expend it to survive and reproduce. Despite the importance of energy as a currency, we know very little about the benefits and costs associated with the amount of energy that animals expend. Past research on mammals has demonstrated that lactation is an energetically costly time of the year because females must expend energy to forage for food, and synthesize milk to raise multiple offspring. We found that the female North American red squirrels that expended the most energy during lactation had the most offspring survive to the following year (i.e. they have greater reproductive fitness). At first glance, it makes intuitive sense that there would be reproductive fitness benefits associated with expending large amounts of energy during lactation. However, our results are interesting because they raise a series of mysteries. The first set of mysteries relates to the mechanism by which elevated energy expenditure during lactation is associated with greater reproductive fitness. The most obvious mechanism is that females that raise larger litter sizes or healthier offspring (i.e. faster growing) have more offspring survive to the following year, but also need to expend more energy to do so. However, this mechanism appears not to be true because there is no relationship between a female’s energy expenditure during lactation and either its litter size or the growth rate of its offspring. Moreover, in order for juveniles to survive until the following year, they must first obtain a territory, then hoard enough cones to survive the winter, and then evade a suite predators. Our results are definitely a mystery because they suggest that if pups are raised by females that expend elevated levels of energy, that this somehow helps them to survive these ecological challenges. The second mystery relates to our finding that females that expended the most energy during lactation experienced no negative consequences. Specifically, we found that females with high levels of energy expenditure during lactation had neither reduced survival to the following year, nor a decreased ability to invest in reproduction the following year. These results are interesting because if there are benefits associated with expending energy during lactation, but no costs, why do not all females expend energy at a high rate?

Image caption: Female red squirrel with one of her pups outside of her grass nest. (Photo credit: Ryan W. Taylor).
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.


The article is available here.

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