Lay Summaries Archive

Read Lay Summaries from previous volumes of Functional Ecology here:

Early View Lay Summaries

 

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

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

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

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

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

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

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

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

 

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

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

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

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

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

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

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

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

 

An insecticide alters personality in jumping spiders.

Raphaël Royauté, Christopher M. Buddle & Charles VincentFemale Eris militaris. Image provided by authors.

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Insecticides are major stressors for many organisms, including beneficial organisms such as predators (e.g., spiders). Most insecticides degrade rapidly after spraying, but traces can persist in the environment. Insecticides often target the nervous system and, at low concentrations, act in a similar way as drugs do in humans. These sublethal doses are unlikely to kill exposed individuals but can affect behaviours such as locomotion, learning capacities and memory. Most studies on insecticides compare changes in average behaviour between exposed and non-exposed populations, but there is another layer of variation that is frequently overlooked: individual variation in behaviour. In any population some individuals are more active, more aggressive or consume more food. These “personality differences” are extremely common in nature and affect an individual’s fitness. The degree to which insecticides can affect personality differences is currently unknown. Our study aims at understanding whether insecticide exposure can alter personality differences in the Bronze Jumping Spider (Eris militaris), an important generalist predator in apple orchards.

We tested how a widely used organophosphate insecticide (phosmet) affected the amount of personality differences in two traits with important fitness consequences for spiders. We tested activity and prey capture behaviours before and after insecticide exposure for 95 individuals and compared those results to a control group of 81 spiders. We found no differences in average behaviour across treatments, but personality differences were reduced by 23% in the insecticide-treated group. We also noticed strong sex-specific variations in the way males and females coped with the insecticide. Males were most affected in the way they explored their environment but their capacity to capture prey remained intact. Females showed a decrease in the relation between activity and prey capture traits. Inactive females typically captured prey more quickly, which was not the case in the insecticide-exposed group.

These results are important because they suggest that scientists frequently underestimate the toxicity of insecticidal compounds by ignoring effects occurring at the individual level. In other words, individuals coming “under the influence” of insecticides typically no longer behave as their personality would predict. These personality alterations may affect a spider’s ability to efficiently suppress pests in agricultural settings.

Image caption: Female Eris militaris. 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.

 

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

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

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

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

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

 

How to package information into feather color patches.

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

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

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

 

Host-plant genetics determines the composition of associated insects.

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

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

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

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

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

 

Moose browsing alters tree diversity effects on birch growth and insect herbivory.

Evalyne W. Muiruri, Harriet T. Milligan, Simon Morath, Julia Koricheva A birch tree damaged by moose (photo by Kalle Rainio).

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Trees are often reported to grow better and suffer less from insect pests in mixed species stands as compared to pure stands. However, negative effects of tree species diversity have also been observed for both tree growth and pest resistance. We tested whether this variation in tree diversity effects is due to impact of browsing mammals as trees in forests often suffer from attacks by both insects and mammals like deer.

The study was conducted in a forest diversity experiment in Finland where trees were planted in single-species and mixed-species plots. Tree growth and insect pest damage were assessed on birch trees which suffered varying degrees of moose browsing in the previous winter. We found that increasing moose browsing intensity modified the magnitude and direction of tree diversity effects on birch. More severe damage by moose reversed the effects of tree diversity on tree growth and pest resistance from negative to positive. Undamaged trees were shorter in mixed stands compared to single species plots but heavily browsed trees grew better in more diverse stands. Similarly, unbrowsed trees were most resistant to insect pests in diverse plots but browsed trees were more susceptible to insect attack in diverse forest stands.

Moose browsing is well known to trigger compensatory re-growth in browsed trees, and we suggest that different effects of browsing on birch trees in mixed and pure stands are due to better re-growth in more diverse mixed-species stands. We have shown that canopies of trees in mixed species stands were more open than in single-species stands. The reduced competition for light in mixed species stands is likely to have increased the re-growth capacity of birch trees and the availability of high-quality foliage for insect pests.

Our study provides the first evidence that the intensity of mammalian browsing might modify tree diversity effects on tree growth and insect pest resistance and might hence explain previously observed variation in plant diversity effects. Mammalian herbivores are therefore key modifiers of forest diversity effects and should be included in future work on the impacts of biodiversity loss on ecosystems.

Image caption: A birch tree damaged by moose (photo by Kalle Rainio).
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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

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

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

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

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

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

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

 

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

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

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

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

 

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

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

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

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

 

The whitefly-associated facultative symbiont suppresses induced plant defenses.

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

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

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

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

 

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

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

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

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

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

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

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

 

Highway to the danger zone: costs of immune system activation in an invasive lizard.

Amber J. Brace, Sam Sheikali& Lynn B. Martin Angry brown anole.

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In any natural environment, organisms will become hosts to many different types of parasites, including bacteria. Once exposed, the immune system of hosts activates to eliminate the parasite. However, this important host protection process is energetically expensive because it is often accompanied by an increase in metabolism and fever. In many populations, immune system activation results in decreased growth, reproductive success and other important processes, likely as an effect of the energetic costs mentioned above. These costs experienced by hosts vary greatly from population to population, and even individual to individual, and are likely partially responsible for the enormous variation that can be seen in how hosts respond to infection.

Many factors, including time of year (breeding or non-breeding season), food availability and ambient temperature can affect the costs incurred by hosts when their immune system is activated. Several studies have shown that the number of parasites an individual is exposed to and/or the number of times an individual is exposed can influence how hosts respond to infection, meaning that these factors play a large role in the costs experienced by exposed hosts. However, how host exposure influences costs of immune activation remains relatively unknown. In this study, we investigated whether exposure to increasing concentrations of an immune-activating component of Salmonella bacteria caused increases in host cost in an invasive lizard in Florida, the brown anole. This species is of ecological concern in Florida because it is very abundant, but little is known about how it may be affecting the spread of parasites. We found that this species of lizard does experience an increase in cost of immune activation with increased exposure to Salmonella bacterial components, but that these costs are quite modest. These findings suggest that because costs associated with infection in this species are low, they may not respond strongly to infection. If this is the case, brown anoles may be more likely to harbor high loads of Salmonella bacteria, which they will subsequently shed into the environment, increasing the probability of exposure in native reptiles.

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

 

The whitefly-associated facultative symbiont suppresses induced plant defenses.

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

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

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

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

 

Sustained heat waves may reduce output of a parasite that causes frog deformities.

Sara H. Paull,Thomas R. Raffel, Bryan E. LaFonte and Pieter T. J. JohnsonInfected snail surrounded by a cloud of cercariae.

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Climate change is altering the size and frequency of temperature fluctuations, yet researchers are only beginning to test how shifts in temperature influence species interactions, including parasitism. A sudden shift in temperature can lead to reduced performance of an organism across a variety of basic functions (e.g., reproductive output, immune defenses). As the organism acclimates to a temperature change over time, its performance can sometimes improve, a process known as ‘beneficial acclimation’. If the new temperature is stressful, however, performance might instead be reduced. We studied how all combinations of temperature shifts from one of 5 initial temperatures (13, 16, 19, 22, 25°C) to one of 5 new temperatures (16, 19, 22, 25, 28°C) influenced the release of the parasitic flatworm Ribeiroia ondatrae from its snail host. We found that parasite release was highest at warmer temperatures shortly after the temperature shift, but parasite release became reduced following periods of more than 48 hours above 25°C. These results are contrary to the beneficial acclimation hypothesis and suggest that temperatures above 25°C are energetically stressful, causing reduced parasite performance following sustained exposure to warmer temperatures. Our results also suggest that infective stages might be stored within snails at lower temperatures for later release when temperatures warm. Ribeiroia’s next hosts are frogs, and the parasite can cause mortality and severe limb deformities in these amphibians, so these results have implications for frog conservation. Exposure of frogs to this deformity-inducing parasite might rise following a sudden temperature increase, or decrease following periods of sustained warm temperatures. Our results also provide insights into potential effects of climate on related trematode parasites of humans like schistosomiasis.

Image caption: Infected snail surrounded by a cloud of cercariae.
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.

 

Personality, plasticity, and predation: linking endocrine and behavioural reaction norms in stickleback fish.

Ines Fürtbauer, Alice Pond, Michael Heistermann & Andrew KingThree-spined stickleback (Gasterosteus aculeatus) and robotic heron. Photographs by Ines Fürtbauer.

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How do animals respond to changes in their environment? Are certain individuals better able to cope with a potential threat? With increasing human activity all over the world, animals have to deal with many more and many different changes happening very quickly. Understanding how animals adapt to such changes is therefore a major and outstanding question for biologists.

Generally, individuals respond to a potential threat with an increase in stress hormone levels – a ‘physiological stress response’ which can mediate the way that individuals behave under threat – the ‘behavioural response’. Across the animal kingdom, individuals of the same species have been shown to consistently vary in their physiological and behavioural responses – they show “personality”. But does personality constrain “plasticity”? In other words, do certain personality types show a reduced capacity to respond to environmental change? This study set out to address this question by investigating the behavioural and physiological responses of three-spined stickleback fish to changes in perceived predation risk.

Across five weeks, we repeatedly exposed female fish to two different perceived predation pressures (low and high) using a robot bird that resembled a heron, a natural predator of the sticklebacks. We collected hormones excreted into the surrounding water via the fishes’ gills, and filmed the fishes’ behaviour. This allowed us to investigate whether individuals show personality, whether and how they hormonally and behaviourally respond to changes in predation risk, whether they are constrained in their response, and whether hormonal and behavioural responses are linked.

The fish showed consistent behavioural and hormonal responses and were less active, shyer, and showed increased stress hormone (i.e. cortisol) levels after exposure to the robot predator. Furthermore, individuals were shyer on days they had higher basal cortisol levels, indicating a link between hormones and behaviour. We found no evidence for variation between animals in their plasticity, suggesting that individuals are not constrained by their personalities in their response to changes in predation pressure. In other words, different personalities are equally capable of responding to a potentially harmful threat. Our study offers novel insight into the interplay of consistent individual differences in hormones and behaviour, as well as plasticity in response to environmental change.

Image caption: Three-spined stickleback (Gasterosteus aculeatus) and robotic heron. Photographs by Ines Fürtbauer.
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.

 

Leaf litter nutrient uptake in an intermittent blackwater river: Influence of tree species and associated biotic and abiotic drivers.

A.S. Mehring, Kevin A. Kuehn, Aaron Thompson, Catherine M. Pringle, Amy D. Rosemond, Matthew R. First, R. Richard Lowrance and George VellidisLeaf litter from the current (left) and previous year (right) on the bottom of an intermittent stream bed in Georgia’s coastal plain. While maple, tupelo, and oak litter can be seen in freshly-fallen litter, only oak litter can be readily distinguished among the older litter.

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Rivers carry nutrients from the land to the oceans and, in doing so, are an important part of global nutrient cycles. As leaves decompose in rivers, they sequester nitrogen (N) and phosphorus (P) that might otherwise be transported downstream. This uptake of nutrients (immobilization) had long been attributed to uptake by microbial decomposers (fungi and bacteria) that colonize and decompose leaves. However, later research showed that microbial biomass in decaying plant litter could only account for a fraction of the total nutrients present, suggesting that additional mechanisms may also be important. One alternative mechanism may be the accumulation of inorganic matter on decaying litter surfaces, which contains charged particles that can bind N and P.

We compared relative contributions of microbial decomposers (biotic) and inorganic matter (abiotic) to nutrient immobilization in decaying leaf litter. We found that P immobilization in leaf litter could not be accounted for by nutrients contained in microbial biomass alone, suggesting that inorganic matter on leaf litter surfaces may play an important abiotic role in P immobilization. In contrast to P, a more complex set of factors appear to influence N immobilization in leaf litter. The combination of nutrients contained in microbial biomass and those bound to inorganic matter could not fully account for the amount of N that was immobilized. A likely source of additional N immobilization is via microbially-mediated processes, particularly the production of N-containing exoenzymes (enzymes excreted outside cells), which can bind with lignocellulose in decaying leaf litter to produce stable N-containing compounds. As a leaf decays, these resistant compounds can remain. Litter with higher concentrations of lignin, such as oak, immobilizes larger amounts of N and P after long periods of decomposition. This supports the idea that lignin, both by slowing mass loss and stabilizing N, may play a role in nutrient immobilization in decaying litter.

Our study shows that nutrient immobilization by decaying leaf litter may be strongly affected by microbial processes (biotic) and inorganic sediment accumulation (abiotic). Our research findings underscore that these processes are essential to understanding detrital nutrient cycling in aquatic ecosystems.

Image caption: Leaf litter from the current (left) and previous year (right) on the bottom of an intermittent stream bed in Georgia’s coastal plain. While maple, tupelo, and oak litter can be seen in freshly-fallen litter, only oak litter can be readily distinguished among the older litter.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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

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

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

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

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

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

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

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

 

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

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

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

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

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

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

 

Links between metabolic rates and growth depend on food availability.

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

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

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

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

 

Cane toads are not directional dispersers.

Gregory P. Brown, Benjamin L. Phillips and Richard Shine Cane toad dispersing. Photograph by David Nelson.

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Cane toads are large and highly toxic amphibians, native to South and Central America. They were released on the east coast of Australia in 1935 to control insect pests, but have become an even greater pest themselves. Over the last 80 years, cane toads have been spreading westwards across the continent at an increasing pace. In every generation, a consistent compass orientation (always heading westwards) would have increased the chances of a toad staying at the fast-moving invasion front. As a result, we predicted that genes for consistent compass directionality may have evolved in the course of the toads’ Australian diaspora. And if so, toads at the invasion front would tend to move consistently in a western direction, whereas toads from older-established populations would disperse in all directions.

To test that prediction, we attached small radio-transmitters to adult cane toads as the invasion front arrived at our study site in tropical Australia, and recorded the directions in which they travelled after we released them. As predicted, toads in the invasion vanguard mostly moved in a westerly direction. As the years passed and we kept on tracking newly-arriving toads, that strong directionality faded. Less than 10 years after the first invasion wave, toads in our study area were moving in all compass directions not just west.

Was that change due to evolution, or (more simply) just because the toads that first arrived came from the east of our study area, and so inevitably moved westwards? That simple explanation looks to be the correct one. When we collected toads from various parts of Australia, and radio-tracked them at a common site, we didn’t find any difference in directionality between toads from different areas. And when we raised their offspring to adulthood and tested them in the same way, a young toad’s dispersal direction wasn’t influenced by that of its parents. Directionality is not heritable. So, although cane toads have evolved many traits over 80 generations of spreading westwards – such as longer legs and more consistent directions of movement from one night to the next – they have not evolved directional dispersal.

Image caption: Cane toad dispersing. Photograph by David Nelson.
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

Phylogenetic niche conservatism – common pitfalls and ways forward.

Tamara Münkemüller, Florian C. Boucher, Wilfried Thuiller, and Sébastien Lavergne The evolution of a trait along a phylogeny.

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The spatial distribution of biodiversity is not random. When we take a walk outside and look at vegetation we may observe that in some places many different species co-occur while in others we see only very few different species. Taking a closer look we may see that there are not only differences in species numbers but that sometimes species look very similar while they are much more dissimilar in other places. The more similar species are, the more similar are their niches, i.e. their adaptation to the local environmental and biotic conditions. If we would have additional information on species evolutionary relatedness we would also see that in some places species are closely related while in others distantly related species co-occur. Niche similarity and relatedness are not independent. Today’s environmental factors and biotic interactions decide how similar species’ niches can be at a given location. Past environments and biotic interactions decided how species niches evolved. Did adaptive ecological and evolutionary processes result in the tendency of species or lineages to retain their ancestral niches over time? This is a common expectation in ecology, which is termed ‘phylogenetic niche conservatism’.

The presence (or absence) of phylogenetic niche conservatism is relevant for a large number of questions in both ecological and evolutionary research. It is for example used in studies that try to understand the ecological drivers of the assembly of species along environmental gradients, that try to estimate the proportion of genetic diversity that will be lost under global change, and that try to predict the evolvability and thus vulnerability of species under global change. The recent rise of large and dated molecular family trees in principle allows for testing for phylogenetic niche conservatism and past biodiversity dynamics. However, the ever-increasing number of studies and their sometimes contrasting results have created confusion and debates not only about the prevalence in nature but also about how to measure and test phylogenetic niche conservatism.

We revisit the different approaches that have been proposed to test for phylogenetic niche conservatism. We show with a combination of simulated data and observed data that there exists no simple way to do this. All suggested simple measures are either uninformative (if their assumptions are considered), require in-depth pre-test of the underlying assumptions and/or require comparisons with related lineages and thus more data. We instead propose more flexible process-based models and give guidelines how to interpret them. These so called Ornstein-Uhlenbeck models allow us to integrate adaptations to different and changing conditions over historical time. They are more data demanding than more simple measures but allow for a better understanding of phylogenetic niche conservatism and thus ultimately for a better comparison between different studies.

Image caption: The evolution of a trait along a phylogeny.
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.

 

Perspective

Is maximum rooting depth all we need to know?

Jesse B. Nippert and Ricardo M. HoldoPhoto provided by authors.

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Most grasslands and savannas are water-limited ecosystems. This description implies that plant species tend to increase growth with increases in water availability in these ecosystems. It has been commonly assumed that the deepest-rooted species may be the best prepared to cope with periods of low water availability. But are other root characteristics as important for maximizing aboveground growth during periods of low-water availability?

In this study, we assessed the role of other root characteristics besides maximum rooting depth as a predictor of aboveground plant growth. We used a dynamic root model to predict changes in aboveground growth when multiple root characteristics were altered. The additional root traits we focused on were related to root-system shape (root distribution through the soil), root physiology (the magnitude of water flow through root conductive tissue), and the dynamics of root-water uptake (the ability to alter water uptake from varying soil zones based on changes in availability). These root characteristics have been frequently reported from coexisting grass, herbaceous non-grass, and woody species from grasslands and savannas. Our results show that the ability to allocate more root biomass to surface soils, flexibly change the location in the soil from which water is extracted, and develop vascular tissue that does not taper with soil depth, result in aboveground growth of a similar magnitude as grassland plant species that produce deep-roots.

In total, these results illustrate multiple potential adaptations of plant species to cope with periods of low-water availability in grasslands and savannas. While maximum rooting depth is an important descriptor for some species and environmental conditions, root traits that describe the morphology, physiology, and ecological plasticity may be equally important predictors of aboveground growth. Incorporating a variety of root traits into ecosystem process models will likely improve description of growth responses to predicted future changes in water availability.

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.

 

Review

New perspectives in ecological succession.

Scott J. Meiners, Marc W. Cadotte, Jason D. Fridley, Steward T. A. Pickett and Lawrence R. Walker A successional field in New Jersey (USA) being colonized by shrubs.  In the background can be seen the forest that serves as the source for many of the plants that establish in the site.  Photo by S. J. Meiners.

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Plant succession, the recovery of vegetation following some sort of disturbance, has been of interest to ecologists for well over a century. Despite this long history, there are still new and exciting approaches to the study of succession that have real promise for improving our understanding of how plant communities change over time. In this paper, we highlight several areas of research that we think will be useful additions to how ecologists traditionally think about succession.

While we often think about succession as occurring within a single site, it happens in a much broader context that is often ignored. The broadest context is that of site history, which may constrain everything that happens in a site, and make the successional processes different from other sites. Based on where a site is in the landscape, some species will arrive there in greater numbers than others, which may also influence how succession proceeds. Finally, all of these plants are growing and interacting in the context of soil microbial communities, which also change over time and can have massive impacts on which species succeed and which fail.

There are two even broader contexts in which we can place succession– evolutionary and geographical. The plant species in an area are the result of long periods of evolutionary interactions that play out in succession. The species that first become abundant are often more closely related than those which dominate later in succession. Therefore, succession results from evolutionary interactions as well. Similarly, plant communities change geographically as the environment changes. Successional processes may similarly change geographically in predictable ways. Neither of these two contexts are particularly well understood, but are very important to developing a broader view of plant succession.

We suggest that building a broader view of succession by examining the characteristics of species – functional ecology – has great potential for increasing our understanding of succession. Doing so should move succession research from focusing on individual characteristics of individual sites towards a broader, more integrative view of our landscapes.

Image caption: A successional field in New Jersey (USA) being colonized by shrubs. In the background can be seen the forest that serves as the source for many of the plants that establish in the site. Photo by S. J. Meiners.
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 makes you attractive for parasites.

Otto Seppälä and Katja LeichtLymnaea stagnalis snail. Photo by Katja Leicht.

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Environmental factors that reduce organisms’ physiological condition, for example shortage of food, can have profound negative effects on them (e.g. reduced survival and fecundity). One generally predicted negative effect is increased susceptibility to parasite infections. This is because the strength of immune system typically depends on the nutritional level of organisms. However, counterintuitively, poor physiological condition has been reported to reduce susceptibility to parasites in a number of species. Such effects may be due to non-immunological factors that contribute more strongly to parasite infection success than host immune function.

By investigating the behaviour of free-swimming larvae of the trematode Echinoparyphium aconiatum we found that the nutritional status of their snail hosts affected host finding by this parasite. Trematode parasites are able to find their snail hosts by using chemical host cues. In our study, this chemo-orientation was modified by snail condition. Parasites were able to locate snails that were well fed and thus in good physiological condition, but not snails that were in poor condition due to starvation.

Our finding shows that host condition can have more complicated effects on host–parasite interactions than predicted based only on the changes in host immune function. Such effects are a likely reason for the reduced susceptibility of snails to infection due to food limitation. From a parasite’s perspective, the use of condition-dependent host cues in host finding can be highly beneficial as it not only enhances transmission in general, but also ensures that parasites infect host individuals that are of high quality and thus most likely to survive in future. Furthermore, evolving counter adaptations to such a transmission strategy can be very difficult for hosts. This is because host defence mechanisms cannot fight against parasites before contact, and reducing feeding to avoid parasites could have many other negative effects.

Image caption: Lymnaea stagnalis snail. Photo by Katja Leicht.
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.

 

Isotopic evidence for edaphic rather than climatic controls over large-scale soil carbon dynamics in alpine ecosystems.

Yuanhe Yang, Chengjun Ji, Leiyi Chen, Jinzhi Ding, Xiaoli Cheng, and David RobinsonVegetation survey and biomass sampling in an alpine meadow on the Tibetan Plateau. The field survey was conducted by the Peking University Sampling Campaign Teams during 2001-2004. Photo credit: Dr. Chengyang Zheng.

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The Tibetan Plateau is the highest and largest plateau in the world, with a mean elevation of 4000 m above sea level, and an area of ~ 2.0×106 km2, about 1.4 times the size of Alaska. The plateau has experienced a faster rate of climate warming over the past several decades compared with other regions in China. Alpine grasslands are the dominant ecosystems on the plateau, and may play an important role in the national carbon cycle since their soils store a large amount of organic carbon. It could be expected that climate warming may accelerate microbial decomposition and thus stimulate carbon release from alpine soils to the atmosphere. However, it is difficult to detect changes in soil carbon stock in these ecosystems over short-time period due to its large pool size, slow turnover time and huge spatial heterogeneity. Stable isotopic measurements along natural gradients provide an alternative approach to infer soil carbon dynamics over broad geographical scales. However, isotopic evidence in alpine ecosystems is scarce.

Using large-scale isotopic measurements obtained from four consecutive field samplings on the Tibetan Plateau, this study aimed to test whether climatic or soil variables regulated large-scale patterns of soil carbon dynamics in alpine ecosystems. In contrast to previous observations in temperate and tropical ecosystems, we demonstrated that soil rather than climatic factors regulated large-scale soil carbon dynamics in alpine ecosystems. Soil silt content and carbon: nitrogen ratio were associated most strongly with carbon isotope discrimination between surface soils and source plants, suggesting that systematic shifts in soil texture and substrate quality may lead to potential fluctuations of soil carbon stock in alpine ecosystems. This finding offers an important contribution to our understanding of the carbon cycle in alpine ecosystems.

Image caption: Vegetation survey and biomass sampling in an alpine meadow on the Tibetan Plateau. The field survey was conducted by the Peking University Sampling Campaign Teams during 2001-2004. Photo credit: Dr. Chengyang Zheng..
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 will climate warming effect the survival and dispersal of endangered green sea turtle hatchlings?

A Catherine Cavallo, Tim Dempster, Michael R. Kearney, Ella Kelly, David Booth, Kate M. Hadden and Tim S. JessopFor a hatchling green turtle, the path to survival is littered with obstacles. Photo credited to Fauxen on Creative Commons..

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During this century, ectothermic (‘cold-blooded’) species, whose body temperature is regulated by the temperature of the environment, are expected to be significantly affected by rapid climate warming. To protect vulnerable species, it is imperative we understand the nature and extent of these effects.

In endangered sea turtles, successful development and dispersal away from the beaches of their birth are key to early life-cycle survival, and thus overall population dynamics. Now this life history stage may be under threat, since it is strongly influenced by environmental temperature, which governs egg survival, hatchling phenotypes and phenotypic performance.

We have developed a new modeling approach that incorporates environmental and developmental processes to predict temperature effects on development and dispersal of green sea turtle hatchlings. This is the first model to consider how temperature simultaneously affects developmental success and offspring phenotypic performance.

We found that rising environmental temperatures in both the incubation and dispersal environment had strong, directional effects on nest survival and key dispersal attributes. Nest temperatures increasingly rose above critical thermal thresholds for egg survival, resulting in a reduction in nesting success of up to 40%. Warmer nest temperatures also affected hatchling phenotypes, producing smaller, weaker hatchlings, which were up to 40% slower than at present, albeit with increased energy stores. Conversely, rising sea surface temperatures aided swimming performance.

Two interesting factors arose from our results that complicate our ability to predict the survival consequences of climate warming on this species. Speed and endurance are key to sea turtle hatchling survival, yet our study found these traits responded differently to temperature. Depending on the predatory environment, this trade-off may mean turtles in some areas are better off while others are disadvantaged. Then there is the contrasting effect of temperature in the developmental and dispersal environments. While it might be hoped that warmer seas could ameliorate the negative effect of nest temperature on swimming performance, this was not demonstrated by our model.

Our study illustrates that climate warming has the potential to significantly affect traits in individuals that are important for recruitment and population stability, an area that has received relatively poor attention in the context of climate change effects on ectotherms.

Image caption: For a hatchling green turtle, the path to survival is littered with obstacles. Photo credited to Fauxen on Creative Commons.
This article can be found here.

 

Linkage and trade-off in trophic morphology and behavioral performance of birds.

Clay Corbin, Lauren Lowenberger & Brandan GrayImage provided by authors.

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For a long time we’ve thought that increasing force during muscular action comes at a cost to the speed at which that action is accomplished. Think about it: at the gym, you can lift heavy weights slowly or light weights quickly. Also, we think there is a pretty tight relationship between the shape of anatomy and its function. An example is Darwin’s finches: large conical bills can apply lots of force (slowly) to crush large seeds, while long, shallow bills tend to close quickly. We wondered if this could be seen in a bird community comprised of bird species from diverse historical and ecological backgrounds. So, we collected three sets of measurements on birds from 18 North American species: bite-force from birds we caught in mistnets, closing velocity from videos of feeding birds, and anatomical measurements from skull specimens housed at the Carnegie Museum of Natural History. We ran some regression analyses and found that, indeed, bird species with larger beaks closed them forcefully; birds with smaller bills closed them quickly. However when regressing force and velocity directly, we were surprised to find only a weak negative relationship, not the graceful negatively sloping relationship seen in human exercise physiology journals. In our data, force is more tightly tied to overall size of the skull and beak, whereas velocity seems to be a product of shape: specifically, the ratio of in-lever length (distance from the articulation between lower jaw and skull to the attachment site of the jaw-closing musculature) to out-lever length (distance from the articulation to the distal tip of the lower jaw). We think the set of anatomical and physiological characteristics associated with high closing force may be decoupled from the set associated with quick closing velocity. Once we corrected the force data for size, the expected trade-off was revealed. However, birds like the ones in your backyard, possibly feeding on hard seeds or snatching flies from the air, can’t suddenly correct for being small (or large!) – they’d just go hungry. Likewise, it is possible that their species’ evolutionary histories include corrections for weak or slow bites, but correcting for one doesn’t necessarily come at a cost in the other.

Image caption: Image provided by authors.
This can be found here.

 

Variation in root morphology of flowering plants is linked to ancestry, but root chemistry is comparable to aboveground tissues.

Oscar J. Valverde-Barrantes, Kurt A. Smemo, and Christopher B. BlackwoodRepresentative fine root systems of Halesia tetraptera (Hal tet, asterdi), Acer saccharum (Ace, sac, rosid) and Magnolia virginiana (Mag vir, magnoliid), showing morphological differences among main angiosperm clades. Picture credits to Peter Blackwood.

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Recent studies have shown that the morphology and chemical composition of fine roots are surprisingly diverse in woody plants. Nevertheless, relatively few studies have attempted to explain the mechanisms behind root trait variation or how those traits are integrated at the entire plant level. For instance, it is expected that root length and tissue nitrogen content should be positively correlated, reflecting a tradeoff between root metabolic activity and surface exposure, as observed in analogous foliar tissues. Moreover, leaf and root traits should be correlated at the entire plant level, guaranteeing a coupling in metabolic activity among organs. Another hypothesis suggests that root morphology evolved from thick and scarcely branched toward thinner and highly branched, reflecting the initial dependency of roots on a symbiotic association with mycorrhizal fungi and subsequent (relative) independence from this association. In this study, we contrasted these two hypotheses by examining the chemical and morphological traits in leaves and fine roots of 34 temperate tree species from three main branches of the flowering plant family tree.

We found a correlation between morphological traits and nitrogen concentration in leaves but not in roots. Unlike leaves, species that were closely related had root traits that were more similar than expected by chance. The oldest angiosperm group (magnoliids) possessed thicker and less branched roots than later, more derived, groups (rosids and asterids). Chemically, lignin levels were higher in rosids than other groups, suggesting that trait combinations vary independently among plant groups. We found only weak correlations between root and leaf morphological traits, but a positive correlation between root and leaf nitrogen levels and other chemical traits. Our study suggests that the evolutionary forces that have shaped root morphology diverge from the tradeoffs commonly observed in leaves aboveground. However, correspondence in nitrogen levels suggests some physiological integration. Overall, our study highlights the fact that root trait patterns do not correspond with the typical patterns described for leaves. Instead, we emphasize the need to incorporate evolutionary history as an important factor explaining root traits in woody plants.

Image caption: Representative fine root systems of Halesia tetraptera (Hal tet, asterdi), Acer saccharum (Ace, sac, rosid) and Magnolia virginiana (Mag vir, magnoliid), showing morphological differences among main angiosperm clades. Picture credits to Peter Blackwood (http://www.blackwoodphoto.com/).
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 female anole lizards retain the ability to respond to testosterone?

Christian L. Cox, Amanda F. Hanninen, Aaron M. Reedy, and Robert M. Cox Female brown anole lizard, Anolis sagrei. Photo provided by author.

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Although selection often favors dramatic differences between the sexes, the evolution of these differences can be constrained because males and females share a genome. In vertebrates, sex hormones can solve this problem by regulating gene expression and development in ways that are unique to each sex. Testosterone in particular is important in male development and is usually found in higher concentrations in males than in females. Nonetheless, testosterone also circulates and serves important biological functions in females. This raises the question of whether sex differences that are regulated by testosterone tend to evolve not only through the coupling of male development to this sex hormone, but also through reductions in the sensitivity of females to testosterone. By altering testosterone levels in juvenile male and female brown anole lizards, we show that females retain the ability to respond to testosterone for a variety of traits, including body size, skeletal growth, metabolism and energy storage, and colorful social signals. Our findings suggest that hormonally mediated differences between the sexes have evolved primarily by linking the development of these traits to higher levels of testosterone in males, and not by altering the way that females respond to testosterone.

Image caption: Female brown anole lizard, Anolis sagrei. Photo provided by author.
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.

 

Water water everywhere: soil water content influences hatchling reptile characteristics.

Brooke L. Bodensteiner, Timothy S. Mitchell, Jeramie T. Strickland and Fredric J. JanzenFigure 1: A) Hatchling painted turtle emerging from nest. (Photo credit: TSM) B) Experimental clutch of painted turtle eggs from this experiment. (Photo credit: BLB).

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Developing reptile eggs are very sensitive to the environmental conditions experienced in the nest. For most reptiles, weather conditions are the most important factor determining the nest environment. Because current climate models predict increases in global temperature, biologists have carefully investigated the influence of incubation temperature on phenotypes of offspring in both the lab and field. However, these climate models also predict marked increases in extreme precipitation events. Many reptiles lay leathery, flexible-shelled eggs that are permeable to water. Thus not only soil temperature, but also soil moisture, can substantially influence phenotypes of developing offspring.

Nearly all the research on the influence of moisture on reptile eggs has occurred in the laboratory and most of this research suggests that wetter conditions produce larger offspring. These observations have not been examined in the field, where complex interactions between environmental variables exist, and moisture levels fluctuate. In this two-year field experiment, we located painted turtle nests and divided their eggs into two artificially constructed nests. One of these nests received supplemental watering throughout incubation while the other was exposed to only natural rainfall.

In 2012, our field site experienced a drought. Watered nests were cooler than control nests and produced larger hatchlings, which upholds the findings of laboratory studies. In 2013, our field site experienced more typical precipitation patterns. Watered nests did not differ from control nests in temperature, and produced smaller hatchlings. We believe that in 2013 our supplemental watering created a nest environment that was too wet and may have caused detrimental effects on the developing offspring. These differences between years suggest that our supplemental watering had context dependent effects on the nest environment and the hatchling phenotypes.

Our findings illustrate the complex interplay between environmental variables that occurs in the field, which is often unexplored in the laboratory, and confirm the importance of corroborating laboratory work with field studies.

Image caption: Figure 1: A) Hatchling painted turtle emerging from nest. (Photo credit: TSM) B) Experimental clutch of painted turtle eggs from this experiment. (Photo credit: BLB).
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.

 

Some don't like it hot: southernmost populations live very close to their thermal limits.

Catarina F. Mota, Aschwin H. Engelen, Ester A. Serrão and Gareth A. Pearson Fucus vesiculosus at the base of cordgrass (Spartina maritima) in the Ria Formosa coastal lagoon. Photo courtesy of the authors.

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The intertidal zone comprises the vertical range of the shore exposed during the lowest low tides and covered by the highest high tides. Intertidal seaweeds are marine species occupying this interface between marine and terrestrial habitats. As major photosynthetic primary producers and structural species in intertidal ecosystems, how seaweeds cope with severe stresses like high temperature and desiccation during exposure to air is important for understanding ecosystem functioning as a whole. Growing in canopies and dense stands, seaweeds modify the physical environment for themselves and associated species, providing distinct microhabitats where thermal conditions can be very different from the prevailing air temperature.

During heat stress, cells express characteristic heat-shock (HS) proteins that repair or remove heat-damaged proteins. The temperatures for the onset, maximum and decline of this heat shock response (HSR) define the thermal range that an organism can endure. Thermal stress is expected to approach physiological limits near the southern edges of a species’ distribution. We collected 4 decades of atmospheric air temperature records, defined HSR parameters in the laboratory, and used sensors to measure the microhabitat thermal environment at local scales in a range-edge population of bladder wrack (Fucus vesiculosus) in southern Portugal, which is now locally extinct.

Laboratory experiments measuring HS gene expression and photosynthetic functioning in F. vesiculosus showed the onset of HSR below 24ºC and a maximum response at 28ºC, while at 36ºC HSR declined (and seaweeds were physiologically damaged). In the field, a mild HSR was seen even in January, and was severe for most of the year. The HSR correlated well with temperatures measured in microhabitats; seaweeds at the edge of the canopy were particularly stressed, while those living under the canopy were somewhat protected from severe HS. Remarkably, although the hottest microhabitat was the canopy surface, seaweeds here showed the lowest HSR, because rapid desiccation leads to a quiescent state that possibly protects them from the damaging effects of heat. Overall, we show that microhabitat temperatures are better predictors of thermal stress than local air temperatures for natural populations, and that these southern populations exist(ed) very close to their thermal physiological limits.

Image caption: Fucus vesiculosus at the base of cordgrass (Spartina maritima) in the Ria Formosa coastal lagoon. Photo courtesy of the 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.

 

Skin turnover increases in amphibians infected with deadly chytrid fungus.

Michel E. B. Ohmer, Rebecca L. Cramp, Craig R. White, & Craig E. Franklin An adult Australia green tree frog (Litoria caerulea). Photo: M. E. B. Ohmer.

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Worldwide, the chytrid fungus (Batrachochytrium dendrobatidis) is wreaking havoc on amphibian populations through the insidious disease chytridiomycosis. What makes this disease so striking is that it infects a wide range of amphibian species globally, leading to population declines and even extinction, despite infecting only the amphibian’s skin.

In amphibians, the skin is an essential organ that functions in water and ion balance and gas exchange. In order to maintain skin health and integrity, amphibians regularly shed their skin. Called sloughing, this process involves removal of the thin outer layer of skin via a series of limb, side, and mouth movements, after which the shed skin is ingested. Regular sloughing is thought to play an important role in immune defence, by removing skin-associated microbes. Crucially, while sloughing is a significant aspect of amphibian skin physiology, we know very little about its relation to the progression of chytridiomycosis.

In order to understand what makes some species more susceptible to this skin disease than others, we have taken a closer look at the unique physiology of amphibian skin shedding. With the help of infrared cameras to capture this elusive behaviour, we examined the relationship between skin sloughing and chytridiomycosis progression by exposing Australian green tree frogs (Litoria caerulea) to the fungus, and monitoring sloughing rates and infection progression over time. We found that frogs sloughed their skin every four days on a predictable cycle, but as chytrid infection intensity increased, sloughing rate also increased to every three days. Surprisingly, sloughing itself did not reduce the abundance of chytrid fungus on the skin.

Our work demonstrates that an increased sloughing rate in infected frogs does not appear to curb the progression of disease. In fact, sloughing may actually increase the detrimental effects of the fungus in terminally ill frogs by further inhibiting water and salt transport across the skin. By measuring sloughing rates directly for the first time, our results shed light on how chytrid fungus interacts with skin maintenance processes, and indicate that variation in skin sloughing frequency may play a role in the observed variation in susceptibility to disease.

Image caption: An adult Australia green tree frog (Litoria caerulea). Photo: M. E. B. Ohmer.
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 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.

 

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.

 

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.

 

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.

 

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.

 

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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Virtual Issue on Ecophysiological forecasting: predicting adaptation and limits to adaptation