Lay Summaries

The below summaries are provided by our authors to help put their research paper into context for the wider scientific community and the general public. Lay summaries for the current issue are here. You can also find all the previous lay summaries by issue, as well as summaries for articles on Early View, in the lay summaries archive.

 

Lay summaries for the current issue

 

You can also find all the previous lay summaries by issue, as well as summaries for articles on Early View, in the lay summaries archive.

 

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

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

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

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

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

Image caption: Ventral aspect of 7-days-old Hynobius retardatus salamander hatchlings reared alone (left) and with conspecifics (right). Photo by Osamu Kishida.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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

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

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

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

 

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

Marta Lopez-Darias, Bieke Vanhooydonck, Raphael Cornette and Anthony HerrelGallotia on Isoplexis.

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

 

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

 

How lizards evolved a fossorial syndrome within the Brazilian Caatingas.

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

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

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

 

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

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

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

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

Image caption: Aerial view of a tropical rainforest, Lambir Hills National park, Sarawak, Malaysia. Photo by Fujio Hyodo.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Inbred Host Plants Promote Enhanced Insect Growth and Flight Capacity.

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

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

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

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

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

 

Age-related deterioration in duckweed.

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

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

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

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

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

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

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

 

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

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

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

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

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

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

Image caption: Contrasting forest types at the study site in the Andes of Ecuador: stunted, open ridge-crest forest (top) and tall lower slope forest near creek (bottom). These two adjacent forest types share only few tree species. Photos: Florian Werner.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Survival of the fattest? Not in the brown anole.

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

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

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

 

A place to hide: how nooks and crannies help species survive in new environments.

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

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

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

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

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

Image caption: Photo credit: Daniel Barrios-O'Neill.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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

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

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

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

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

Image caption: Overview of the Manu Gradient, photo taken from the field site at 3000 m elevation with the lowland site in the background.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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

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

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

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

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

Image caption: Ultrasonographic picture of a developing embryo (Vipera aspis).
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Silicon concentration and population dynamics of voles.

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

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

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

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

Image caption: Root vole, Microtus oeconomus. Photo courtesy of K. Zub.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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

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

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

Image caption: Implications of lifespan variation within a leaf cohort for evaluation of the optimal timing of leaf shedding.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Impacts of repeated stress events on an overwintering insect.

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

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

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

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

Image caption: Late-instar Choristoneura fumiferana caterpillar. Photo courtesy of Jerald E. Dewey, USDA Forest Service, United States, downloaded from Wikimedia Commons.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Variability in potential to exploit different soil organic phosphorus compounds among tropical montane tree species.

Brian S. Steidinger, Benjamin L. Turner, Adrianna Corrales, and James W. DallingGrow house at the Fortuna Forest Reserve.

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The mineral nutrients that plants need to grow and reproduce occur in the soil in a variety of chemical forms. This diversity of form makes it possible for plants to specialize in the acquisition of specific forms, which can reduce competition over growth-limiting nutrients and promote species coexistence. A key nutrient is phosphorus (P), which most plants are helped to acquire by a fungal partner, known as a mycorrhiza. Of the two commonest types of mycorrhiza, one actually penetrates plant roots, while the other forms a sheath around the root.

Previous work suggests plants that associate with these two different functional groups of mycorrhizas differ in their ability to acquire P from organic vs. inorganic sources. We tested this hypothesis at the Fortuna Forest Reserve, a tropical montane forest along Panama’s Central Cordillera, where representative species from both mycorrhizal groups and non-mycorrhizal tree species coexist. First, we collected seedlings of tree species with different mycorrhizal associations from the field, sampled their root systems, and measured the activity of enzymes that allow plants to exploit organic P. Next, we took the same tree species, exposed them to P exclusively in one of four different chemical forms (three organic + one inorganic), and gauged their performance.

Our results confirm that specialized plants that lack mycorrhizal fungi are better able to exploit a specific form of organic P that is unavailable to the mycorrhizal plant species. This difference appears to be related to a markedly higher activity of enzymes that attack organic P. In contrast, we found no evidence that plants associating with different types of mycorrhiza differ in their ability to exploit organic and inorganic forms of P. Overall, our results support the potential for P partitioning to occur in a tropical montane forest, but suggest that it occurs more coarsely among functional groups than previously imagined.

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

 

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

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

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

Image caption: A male brown anole lizard displaying its colorful dewlap. Photograph by Duncan J. Irschick.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Changes in resource availability have profound consequences for the microbial communities of tropical forest soils.

Nicolas Fanin, Stephan Hättenschwiler, Heidy Schimann & Nathalie Fromin Fungi are main actors of leaf litter decomposition in the tropical forest.

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Tropical forest ecosystems play a key role in the global carbon (C) cycle. In these forests that grow on highly weathered and nutrient-impoverished soils, a mechanistic understanding of how resource availability controls soil C dynamics is urgently needed for accurate predictions of global change effects on the C cycle.

Because soil microorganisms (i.e. bacteria and fungi) have different nutrient requirements, we expected the soil microbial community and the processes it drives to strongly respond to fertilization with different major nutrient elements. We report the results of the first combined fertilization experiment with cellulose (C), urea (nitrogen) and phosphate (phosphorus) in a nutrient-poor tropical rainforest of French Guiana.

After two years of fertilization, we showed that changes in resource availability had profound consequences for soil microorganisms, with clear shifts in the structure and function of the soil microbial community and its ability to process various C substrates. In particular, phosphorus addition enhanced both bacterial and fungal biomasses and overall microbial activity, as well as the ability of the soil microbial community to use a wide range of C substrates. However, the strongest effects of phosphorus fertilization were observed with the simultaneous addition of nitrogen and or C, showing limitation of soil microorganisms by multiple, interacting nutrient elements.

The reported multiple element control of soil microbial biomass, community structure and activity may contribute to a better understanding of spatial and temporal heterogeneity in microbial community structure, their associated functions and the dynamics of C and nutrients in tropical ecosystems.

Image caption: Fungi are main actors of leaf litter decomposition in the tropical forest.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Oxidative stress in breeding northern elephant seals.

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

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

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

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

 

Swimming loss and recovery in the Atlantic silverside.

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

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

Image caption: Adult Atlantic silversides collected in little neck bay, Long Island, NY USA. Photo credited to Kestrel O. Perez..
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Community phylogenetics and ecosystem functioning

Clarifying the discussion of how environmental variation shapes community diversity.

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

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

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

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

Image caption: In the Central Valley of California, USA, small depressions in the ground can fill with rainwater in the winter, creating a vernal pool habitat. The dominant plant species (shown here in bloom) that are found in these pools can tolerate immersion in the rainwaters, while the flooded conditions exclude many of the surrounding grassland species. This process of environmental filtering, seen here at a small scale, shapes patterns of biodiversity across the planet. Photo credited to Nathan Kraft.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Plant uptake elements as influenced by phylogeny, soil and climate.

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

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

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

Image caption: Primulina bullata growing calcareous soils (Photo credit: Ming Kang).
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Hard work, dominance and health in a Kalahari bird.

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

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

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

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

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

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

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

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

 

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

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

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

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

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

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

Image caption: Kittiwakes breeding at the study site on Middleton Island, Alaska, USA. Photo by Jorg Welcker.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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

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

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

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

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

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

 

Food jumpstarts feather moult.

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

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

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

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

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

Image caption: A swamp sparrow moulting throat, face, and crown feathers in eastern North Carolina. Photo by Jeff Lewis, used with permission.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

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