Culex pipiens and Culex restuans larval interactions shape the bacterial communities in container aquatic habitats

Container aquatic habitats host a community of aquatic insects, primarily mosquito larvae that browse on container surface microbial biofilm and filter-feed on microorganisms in the water column. We examined how the bacterial communities in these habitats respond to feeding by larvae of two container-dwelling mosquito species, Culex pipiens and Cx. restuans. We also investigated how the microbiota of these larvae is impacted by intra- and interspecific interactions. Microbial diversity and richness were significantly higher in water samples when mosquito larvae were present, and in Cx. restuans compared to Cx. pipiens larvae. Microbial communities of water samples clustered based on the presence or absence of mosquito larvae and were distinct from those of mosquito larvae. Culex pipiens and Cx. restuans larvae harbored distinct microbial communities when reared under intraspecific conditions and similar microbial communities when reared under interspecific conditions. These findings demonstrate that mosquito larvae play a major role in structuring the microbial communities in container habitats and that intra- and interspecific interactions in mosquito larvae may shape their microbiota. This has important ecological and public health implications since larvae of the two mosquito species are major occupants of container habitats while the adults are vectors of West Nile virus.

Importance of Genetic-Fitness Correlations for the Conservation of Amphibians

Endangered animals suffer from isolation of their habitats. Isolation leads to a reduction in population size as well as a decrease in genetic diversity and a concomitant increase in the risk of extinction. Amphibians are the most endangered vertebrate class. Besides habitat loss, fragmentation and isolation, amphibians are threatened by emerging diseases e.g., chytrid fungus or Ranavirus. By employing experiments, researchers investigate whether changes in genetic diversity within or among isolated populations affect amphibian fitness. While genetic diversity estimates are based on molecular markers, typically microsatellites, fitness is mostly measured as tadpole performance in rearing experiments often under varying environmental conditions. Tadpole performances (e.g., body mass, growth rate and survival) have been found to be negatively affected by low genetic diversity, as several studies have found a positive association between genetic diversity and these fitness traits. Moreover, infection with pathogens also seems to be more likely in individuals or populations with lower genetic diversity. Overall, these genetic-fitness correlations seem to be more pronounced or detectable in smaller, declining populations but not in larger populations. Genomic studies, which sample a larger fraction of the genome, are still scarce in the conservation genetic literature on amphibians. These are likely to increase in upcoming years and may reveal adaptive variants that protect against dangerous pathogens or environmental changes. Altogether, genetic-fitness correlation studies should be a priority in order to develop effective management plans for the genetic rescue of isolated, imperilled amphibian populations.

Species-specific model to predict amphibian metamorphosis

Exploring the timing of life-history transitions has been a pivotal focus in the field of evolutionary ecology. Studies on amphibian metamorphosis are well suited to investigate this aspect. We propose a species-specific model to predict the optimal metamorphosis point for frog individuals with different larval growth trajectories. Because overall fitness will be determined throughout both aquatic and terrestrial stages, we included growth and survival rates of aquatic and terrestrial stages in the fitness equation. Then we conducted a rearing experiment on a brown frog, Rana ornativentris, as an example to obtain the size at metamorphosis, larval period, and larval growth trajectory. Based on these results, we determined the model's parameters to fit the actual metamorphosis patterns. Because the parameters are supposed to be evolutionarily maintained, our data-driven approach enabled obtaining fundamental ecological information (evolutionally-based life-history parameters) of the target species. Comparing the parameters among species will allow us to understand the mechanisms in determining life-history transition more deeply.

The role of environmental variation in mediating fitness trade-offs for an amphibian polyphenism

Fitness trade-offs are a foundation of ecological and evolutionary theory because trade-offs can explain life history variation, phenotypic plasticity, and the existence of polyphenisms. Using a 32-year mark-recapture dataset on lifetime fitness for 1093 adult Arizona tiger salamanders (Ambystoma mavortium nebulosum) from a high elevation, polyphenic population, we evaluated the extent to which two life history morphs (aquatic paedomorphs vs. terrestrial metamorphs) exhibited fitness trade-offs in breeding and body condition with respect to environmental variation (e.g. climate) and internal state-based variables (e.g. age). Both morphs displayed a similar response to higher probabilities of breeding during years of high spring precipitation (i.e. not indicative of a morph-specific fitness trade-off). There were likely no climate-induced fitness trade-offs on breeding state for the two life history morphs because precipitation and water availability are vital to amphibian reproduction. Body condition displayed a contrasting response for the two morphs that was indicative of a climate-induced fitness trade-off. While metamorphs exhibited a positive relationship with summer snowpack conditions, paedomorphs were unaffected. Fitness trade-offs from summer snowpack are likely due to extended hydroperiods in temporary ponds, where metamorphs gain a fitness advantage during the summer growing season by exploiting resources that are unavailable to paeodomorphs. However, paedomorphs appear to have the overwintering fitness advantage because they consistently had higher body condition than metamorphs at the start of the summer growing season. Our results reveal that climate and habitat type (metamorphs as predominately terrestrial, paedomorphs as fully aquatic) interact to confer different advantages for each morph. These results advance our current understanding of fitness trade-offs in this well-studied polyphenic amphibian by integrating climate-based mechanisms. Our conclusions prompt future studies to explore how climatic variation can maintain polyphenisms and promote life history diversity, as well as the implications of climate change for polyphenisms.

Spadefoot Pelobates vespertinus (Amphibia, Pelobatidae) as a transmitter of fatty acids from water to land in a forest-steppe floodplain

The transfer of biomass and polyunsaturated fatty acids by the spadefoot P. vespertinus (previously subspecies of P. fuscus) from aquatic to terrestrial ecosystems was studied for five years in small floodplain water bodies of a forest-steppe zone. Average emergence of metamorphs from unit of water area, wet mass was 6.7 g m^-2 year^-1. A ratio of the emergence to biomass was calculated and represented as E/B coefficient (an analog of P/B production/biomass coefficient). The average E/B was found to be 0.038 year^-1. The introduced coefficient can be used for a coarse estimation of the emergence on the basis of tadpole biomass measurements. A considerable partitioning of tadpoles and metamorphs in the composition of fatty acids in their biomass was revealed. Tadpoles had significantly higher mean levels (percent of total fatty acids) of 16:0, 16:1n-9, 18:0, 20:5n-3 and 22:5n-3, while metamorphs had significantly higher levels of 14:0, 15:0, 17:0, 17:1n-8, 18:2n-6, 20:2n-6, 20:4n-6 and 22:5n-6, likely due to the shifting to terrestrial food. Metamorphs had significantly higher content of total fatty acids, mg g^-1 of wet weight, and, in spite of lower level, they had significantly higher content of eicosapentaenoic acid (20:5n-3, EPA) than tadpoles. Metamorphs also had significantly higher content of docosahexaenoic acid (22:6n-3, DHA) and sum of EPA + DHA than tadpoles. Average flux of EPA + DHA from unit of water area with metamorphs was 3.27 mg m^-2 year^-1. The metamorphs appeared to be qualitatively and quantitatively prominent prey for a number of terrestrial consumers.

Projected Climate and Hydroregime Variability Constrain Ephemeral Wetland-Dependent Amphibian Populations in Simulations of Southern Toads

Amphibian populations are threatened globally by stressors, including diminishing availability of suitable wetland breeding sites, altered hydroregimes driven by changing weather patterns, and exposure to contaminants. Ecological risk assessment should encompass spatial and temporal scales that capture influential ecological processes and demographic responses. Following the PopGUIDE framework of population model development for risk assessment, we used matrix population models, in conjunction with existing hydroregime predictions, under a climate change scenario to evaluate the effects of environmental stochasticity and aquatic pesticide exposure on amphibians that are dependent on ephemeral wetlands. Using southern toads (Anaxyrus terrestris) as an example, we simulated population dynamics with breeding success dependent on hydroregime suitability. Years were defined as optimal, marginal, or insufficient for successful toad recruitment, based on the duration of their potential breeding season and rate of larval development to metamorphosis. We simulated both probabilistic and chronologically specific population projections, including variable annual fecundity, based on hydroregime suitability and reduced larval survival from carbaryl exposure. In our simulations, populations were more negatively impacted by prolonged drought, and consequently multiple sequential years of reproductive failure, than by aquatic pesticide exposure. These results highlight the necessity of reliable climate projections to accurately represent the effects of altered hydroregimes on amphibian populations. Risk assessment approaches could be improved with flexible modifications that allow inclusion of various extrinsic stressors and identification of demographic and ecological vulnerabilities when precise data are lacking.

Different time patterns of the presence of red-eared slider influence the ontogeny dynamics of common frog tadpoles

The coexistence of species in a given community depends on the set of species involved and the timing of their interactions. Many native communities are increasingly forced to face both direct and indirect pressures from new alien predators, which, in extreme cases, can lead to the extinction of prey populations. In this study, we examine the dynamics of the ontogeny of common frog (Rana temporaria) tadpoles under different time patterns of an alien predator-the red-eared slider (Trachemys scripta elegans) presence. We found that the tadpoles had a longer larval period and were smaller in size at metamorphosis and lower in body mass when the predator was present in early development than when the tadpoles developed without a predator. The early presence of a predator conspicuously reduced the growth increments of the tadpoles at early development. After the removal of the predator, growth accelerated above the level measured under the conditions of both the late predator and no predator. However, these growth rates did not exceed the growth rates of equally sized tadpoles in the other treatments and therefore were not sufficient to compensate for the growth slowdown in the first part of development. The presence of a predator in late tadpole development influenced neither the time to metamorphosis nor size/body mass at metamorphosis. In conclusion, the predator had the effect on metamorphosis traits only if it was present in the early development of tadpoles.

Effects of elevated temperature, reduced hydroperiod, and invasive bullfrog larvae on pacific chorus frog larvae

Climate change and invasive species threaten many ecosystems, including surface freshwater systems. Increasing temperatures and reduced hydroperiod due to climate change may promote the persistence of invasive species and facilitate new invasions due to potentially higher tolerance to environmental stress in successful invaders. Amphibians demonstrate high levels of plasticity in life history characteristics, particularly those species which inhabit both ephemeral and permanent water bodies. We tested the influence of two projected effects of climate change (increased temperature and reduced hydroperiod) on Pacific chorus frog (Pseudacris regilla) tadpoles alone and in combination with the presence of tadpoles of a wide-spread invasive amphibian, the American bullfrog (Lithobates catesbeianus). Specifically, we explored the effects of projected climate change and invasion on survival, growth, mass at stage 42, and development rate of Pacific chorus frogs. Direct and indirect interactions between the invasive tadpole and the native tadpole were controlled via a cage treatment and were included to account for differences in presence of the bullfrog compared to competition for food resources and other direct effects. Overall, bullfrogs had larger negative effects on Pacific chorus frogs than climate conditions. Under future climate conditions, Pacific chorus frogs developed faster and emerged heavier. Pacific chorus frog tadpoles developing in the presence of American bullfrogs, regardless of cage treatment, emerged lighter. When future climate conditions and presence of invasive American bullfrog tadpoles were combined, tadpoles grew less. However, no interaction was detected between climate conditions and bullfrog presence for mass, suggesting that tadpoles allocated energy towards mass rather than length under the combined stress treatment. The maintenance of overall body condition (smaller but heavier metamorphs) when future climate conditions overlap with bullfrog presence suggests that Pacific chorus frogs may be partially compensating for the negative effects of bullfrogs via increased allocation of energy towards mass. Strong plasticity, as demonstrated by Pacific chorus frog larvae in our study, may allow species to match the demands of new environments, including under future climate change.

Bufadienolides from the Eggs of the Toad Bufo bufo gargarizans and Their Antimelanoma Activities

Toads produce potent toxins, named bufadienolides, to defend against their predators. Pharmacological research has revealed that bufadienolides are potential anticancer drugs. In this research, we reported nine bufadienolides from the eggs of the toad Bufo bufo gargarizans, including two new compounds (1 and 3). The chemical structures of 1 and 3, as well as of one previously reported semisynthesized compound (2), were elucidated on the basis of extensive spectroscopic data interpretation, chemical methods, and X-ray diffraction analysis. Compound 1 is an unusual 19-norbufadienolide with rearranged A/B rings. A biological test revealed that compounds 2 and 4-8 showed potent cytotoxic activities toward human melanoma cell line SK-MEL-1 with IC₅₀ values less than 1.0 μM. A preliminary mechanism investigation revealed that the most potent compound, 8, could induce apoptosis via PARP cleavage, while 5 and 6 significantly suppressed angiogenesis in zebrafish. Furthermore, an in vivo biological study showed that 5, 6, and 8 inhibit SK-MEL-1 cell growth significantly.

Carryover effects and the evolution of polyphenism

An individual’s early-life environment and phenotype often influence its traits and performance as an adult. We investigated whether such ‘carryover effects’ are associated with alternative, environmentally-induced phenotypes (‘polyphenism’), and, if so, whether they influence the evolution of polyphenism. To do so, we studied Mexican spadefoot toads, Spea multiplicata, which have evolved a polyphenism consisting of two, dramatically different forms: a carnivore morph and an omnivore morph. We sampled both morphs from a fast-drying and a slow-drying pond and reared them to sexual maturity. Larval environment (pond) strongly influenced survival as well as age and size at metamorphosis and sexual maturity; i.e. environment-dependent carryover effects were present. By contrast, larval phenotype (morph) did not affect life-history traits at sexual maturity; i.e. phenotype-dependent carryover effects were absent. These results are consistent with theory, which suggests that by amplifying selective trade-offs in heterogenous environments, environment-dependent carryover effects might foster the evolution of polyphenism. At the same time, by freeing selection to refine a novel phenotype without altering the existing form, the absence of phenotype-dependent carryover effects might enable polyphenism to evolve in the first place. Generally, carryover effects might play an underappreciated role in the evolution of polyphenism.

How to recover from a bad start: size at metamorphosis affects growth and survival in a tropical amphibian

Background

In species with complex life cycles, size at metamorphosis is a key life-history trait which reflects the complex interactions between costs and benefits of life in the aquatic and terrestrial environments. Whereas the effects of a deteriorating larval habitat (e.g. pond desiccation) on triggering an early metamorphosis have been extensively investigated in amphibians, the consequences of the resulting reduced size at metamorphosis on fitness in the post-metamorphic terrestrial stage remain poorly understood. We tested the hypothesis that a smaller size at metamorphosis negatively affects performance and survival in the ensuing terrestrial stage. Using as model a tropical amphibian (Ceratophrys stolzmanni) showing a large phenotypic plasticity in metamorphosing traits, we evaluated the effects of size at metamorphosis on fitness-related trophic and locomotor performance traits, as well as on growth and survival rates.

Results

Our results support the hypothesis that a larger size at metamorphosis is correlated with better survival and performance. The survival rate of large metamorphosing individuals was 95%, compared to 60% for those completing metamorphosis at a small size. Locomotor performance and gape size were positively correlated with body size, larger animals being more mobile and capable to ingest larger prey. However, smaller individuals achieved higher growth rates, thus reducing the size gap.

Conclusions

Overall, size at metamorphosis affected profoundly the chances of survival in the short term, but smaller surviving individuals partly compensated their initial disadvantages by increasing growth rates.

Slow life-history strategies are associated with negligible actuarial senescence in western Palaearctic salamanders

Actuarial senescence has been viewed for a long time as an inevitable and uniform process. However, the work on senescence has mainly focused on endotherms with deterministic growth and low regeneration capacity during the adult stage, leading to a strong taxonomic bias in the study of ageing. Recent studies have highlighted that senescence could indeed display highly variable trajectories that correlate with species life-history traits. Slow life histories and indeterminate growth seem to be associated with weak and late senescence. Furthermore, high regenerative abilities could lead to negligible senescence in ectotherms. However, demographic data for species that would allow testing of these hypotheses are scarce. Here, we investigated senescence patterns in 'true salamanders' from the western Palaearctic. Our results showed that salamanders have slow life histories and that they experience negligible senescence. This pattern was consistent at both intra- and interspecific levels, suggesting that the absence of senescence may be a phylogenetically conserved trait. The regenerative capacities of salamanders, in combination with other physiological and developmental features such as an indeterminate growth and a low metabolic rate, probably explain why these small ectotherms have lifespans similar to that of large endotherms and, in contrast with most amniotes, undergo negligible senescence. Our study seriously challenges the idea that senescence is a ubiquitous phenomenon in the tree of life.

Spatial capture-recapture reveals age- and sex-specific survival and movement in stream amphibians

Life-history information sets the foundation for our understanding of ecology and conservation requirements. For many species, this information is lacking even for basic demographic rates such as survival and movement. When survival and movement estimates are available, they are often derived from mixed demographic groups and do not consider differences among life stages or sexes, which is critical, because life stages and sexes often contribute differentially to population dynamics. We used hierarchical models informed with spatial capture-mark-recapture data of Ascaphus montanus (Rocky Mountain tailed frog) in five streams and A. truei (coastal tailed frog) in one stream to estimate variation in survival and movement by sex and age, represented by size. By incorporating survival and movement into a single model, we were able to estimate both parameters with limited bias. Annual survival was similar between sexes of A. montanus [females = 0.885 (95% CI 0.614-1), males = 0.901 (0.657-1)], but was slightly higher for female A. truei [0.836 (0.560-0.993)] than for males [0.664 (0.354-0.962)]. Survival of A. montanus peaked at mid-age, suggesting that lower survival of young and actuarial senescence may influence population demographics. Our models suggest that younger A. montanus moved farther than older individuals, and that females moved farther than males in both species. Our results provide uncommon insight into age- and sex-specific rates of survival and movement that are crucial elements of life-history strategies and are important for modeling population growth and prescribing conservation actions.

Survival cost to relocation does not reduce population self-sustainability in an amphibian

Relocations are increasingly popular among wildlife managers despite often low rates of relocation success in vertebrates. In this context, understanding the influence of extrinsic (e.g., relocation design, habitat characteristics) and intrinsic factors (e.g., age and sex) on demographic parameters, such as survival, that regulate the dynamics of relocated populations is critical to improve relocation protocols and better predict relocation success. We investigated survival in naturally established and relocated populations of yellow-bellied toads (Bombina variegata), an amphibian that was nearly extinct in Belgium by the late 1980s. We quantified survival at three ontogenetic stages (juvenile, subadult, and adult) in the relocated population, the source population, and a control population. In the relocated population, we quantified survival in captive bred individuals and their locally born descendants. Then, using simulations, we examined how survival cost to relocation affects the self-sustainability of the relocated population. We showed that survival at juvenile and subadult stages was relatively similar in all populations. In contrast, relocated adult survival was lower than adult survival in the source and control populations. Despite this, offspring of relocated animals (the next generation, regardless of life stage) survived at similar rates to individuals in the source and control populations. Simulations revealed that the relocated population was self-sustaining under different scenarios and that the fate (e.g., stability or increase) of the simulated populations was highly dependent on the fecundity of relocated adults and their offspring. To summarize, our results indicate that survival in relocated individuals is lower than in non-relocated individuals but that this cost (i.e., reduced survival) disappears in the second generation. A finer understanding of how relocation affects demographic processes is an important step in improving relocation success of amphibians and other animals.

Survival cost to relocation does not reduce population self-sustainability in an amphibian

Relocations are increasingly popular among wildlife managers despite often low rates of relocation success in vertebrates. In this context, understanding the influence of extrinsic (e.g., relocation design, habitat characteristics) and intrinsic factors (e.g., age and sex) on demographic parameters, such as survival, that regulate the dynamics of relocated populations is critical to improve relocation protocols and better predict relocation success. We investigated survival in naturally established and relocated populations of yellow-bellied toads (Bombina variegata), an amphibian that was nearly extinct in Belgium by the late 1980s. We quantified survival at three ontogenetic stages (juvenile, subadult, and adult) in the relocated population, the source population, and a control population. In the relocated population, we quantified survival in captive bred individuals and their locally born descendants. Then, using simulations, we examined how survival cost to relocation affects the self-sustainability of the relocated population. We showed that survival at juvenile and subadult stages was relatively similar in all populations. In contrast, relocated adult survival was lower than adult survival in the source and control populations. Despite this, offspring of relocated animals (the next generation, regardless of life stage) survived at similar rates to individuals in the source and control populations. Simulations revealed that the relocated population was self-sustaining under different scenarios and that the fate (e.g., stability or increase) of the simulated populations was highly dependent on the fecundity of relocated adults and their offspring. To summarize, our results indicate that survival in relocated individuals is lower than in non-relocated individuals but that this cost (i.e., reduced survival) disappears in the second generation. A finer understanding of how relocation affects demographic processes is an important step in improving relocation success of amphibians and other animals.

Compounding effects of climate change reduce population viability of a montane amphibian

Anthropogenic climate change presents challenges and opportunities to the growth, reproduction, and survival of individuals throughout their life cycles. Demographic compensation among life-history stages has the potential to buffer populations from decline, but alternatively, compounding negative effects can lead to accelerated population decline and extinction. In montane ecosystems of the U.S. Pacific Northwest, increasing temperatures are resulting in a transition from snow-dominated to rain-dominated precipitation events, reducing snowpack. For ectotherms such as amphibians, warmer winters can reduce the frequency of critical minimum temperatures and increase the length of summer growing seasons, benefiting post-metamorphic stages, but may also increase metabolic costs during winter months, which could decrease survival. Lower snowpack levels also result in wetlands that dry sooner or more frequently in the summer, increasing larval desiccation risk. To evaluate how these challenges and opportunities compound within a species' life history, we collected demographic data on Cascades frog (Rana cascadae) in Olympic National Park in Washington state to parameterize stage-based stochastic matrix population models under current and future (A1B, 2040s, and 2080s) environmental conditions. We estimated the proportion of reproductive effort lost each year due to drying using watershed-specific hydrologic models, and coupled this with an analysis that relates 15 yr of R. cascadae abundance data with a suite of climate variables. We estimated the current population growth (λ_s ) to be 0.97 (95% CI 0.84-1.13), but predict that λ_s will decline under continued climate warming, resulting in a 62% chance of extinction by the 2080s because of compounding negative effects on early and late life history stages. By the 2080s, our models predict that larval mortality will increase by 17% as a result of increased pond drying, and adult survival will decrease by 7% as winter length and summer precipitation continue to decrease. We find that reduced larval survival drives initial declines in the 2040s, but further declines in the 2080s are compounded by decreases in adult survival. Our results demonstrate the need to understand the potential for compounding or compensatory effects within different life history stages to exacerbate or buffer the effects of climate change on population growth rates through time.

Urban plums and toads: do fleshy fruits affect the post-metamorphic growth of amphibians?

BACKGROUND

The main aim of the study was to analyse the influence of fleshy fruits (plums) on the post-metamorphic growth and feeding behaviour of the green toad Bufotes viridis. We tested the following two hypotheses: (1) juveniles of the green toad are characterised by faster growth in conditions involving fallen plums Prunus cerasifera due to the associated presence of more varied food such as invertebrates; (2) green toads exhibit more active feeding behaviour in the presence of fleshy fruits.

METHODS

A total of 120 fresh metamorphs of the green toad were randomly assigned to one of four groups: two experimental groups with fleshy plums and two other groups as controls (without fruits). Each group was kept in an enclosure to which wild invertebrates had free access. Each individual toad was measured for snout-vent length (mm) and body mass (g) every other day for 30 days. In order to determine whether fallen plums influence the feeding behaviour of toads, the number of active and hidden (under an artificial shelter) individuals was also noted.

RESULTS

The results showed that green toads from both enclosures with plums were characterised by more rapid growth than individuals from the control treatments. Simultaneously, in the enclosure with fleshy fruits, greater species richness of wild invertebrates was observed. No differences in active feeding behaviour were noted between control groups and groups with plums.

DISCUSSION

Fleshy fruits, upon falling, attract many types of invertebrates; thus they may represent good dietary supplements for fresh amphibian metamorphs. Therefore, the presence of fruit trees close to a breeding site might influences the post-metamorphic growth of amphibians, but not their feeding behaviour. The presence of insects associated with fallen fruit seems to favour the occurrence of amphibian populations, which is particularly important, since, due to political and social pressure, numbers of fruit trees are currently being reduced. To our knowledge, no previous study has investigated the potential influence of the presence of fruit trees on the growth and behaviour of anurans.

High juvenile mortality in amphibians during overwintering related to fungal pathogen exposure

The result of pathogen exposures may depend upon trade-offs in energetic demands for immune responses against host growth and survival. Environmental conditions may influence these trade-offs by affecting host size, or trade-offs may change across seasons, altering impacts of pathogens. We exposed northern leopard frog Lithobates pipiens tadpoles to different larval environments (low leaf litter, high density of conspecifics, atrazine, caged fish, or controls) that influenced size at metamorphosis. Subsequently, we exposed metamorphs to Batrachochytrium dendrobatidis (Bd), a fungal pathogen, just after metamorphosis and/or prior to overwintering 12 wk later. Bd exposure dramatically reduced survival during overwintering, with the strongest effects when hosts were exposed at both time points. Larval environments resulted in differences in host size. Those exposed to caged fish were 2.5 times larger than the smallest (those exposed to high density of conspecifics), but larval environment did not influence Bd effects on growth and survival. The largest frogs exposed to caged fish had greater survival through overwintering, but in the absence of Bd. We built stage-structured models to evaluate if overwinter mortality from Bd is capable of having effects on host populations. Our models suggest that Bd exposure after metamorphosis or before overwintering can reduce population growth rates. Our study demonstrates that hosts suffer little effects of Bd exposures following metamorphosis and that small body size did not hamper growth and survival. Instead, we provide evidence that winter mortality from Bd exposure is capable of reducing population sizes, providing a plausible mechanism for amphibian declines in temperate regions.

Resilience to climate variation in a spatially structured amphibian population

Understanding the impact of weather fluctuations on demographic parameters is of crucial interest to biodiversity research in a context of global climate change. Amphibians are valuable candidates for investigating this topic due to their strong physiological dependence on water availability and temperature. In this study, we took advantage of data from a long-term capture-mark-recapture (CMR) monitoring program of a great crested newt (Triturus cristatus) population inhabiting a 12-pond archipelago in southeastern France. We investigated the interactions between vital rates (survival and recruitment), the internal structure of the population, and climatic variables both at a local and a regional (North Atlantic Oscillation: NAO) scale. Overall, we found a weak relationship between climatic variables and the survival of large-bodied newts. The only strong relationship was found to be a high NAO index during the post-breeding period, suggesting that dry, hot summers negatively impact survival. In terms of recruitment, the results indicated that hot weather during the activity period had delayed deleterious effects on adult recruitment two years later, suggesting high larval and juvenile mortality due to unsuitable growing conditions. Recruitment was also impacted by a high NAO index during the overwintering period preceding recruitment, suggesting that mild weather increases the mortality of juveniles, probably by enhancing the depletion of energy reserves without any possibility of refueling.

Life history tactics shape amphibians' demographic responses to the North Atlantic Oscillation

Over the last three decades, climate abnormalities have been reported to be involved in biodiversity decline by affecting population dynamics. A growing number of studies have shown that the North Atlantic Oscillation (NAO) influences the demographic parameters of a wide range of plant and animal taxa in different ways. Life history theory could help to understand these different demographic responses to the NAO. Indeed, theory states that the impact of weather variation on a species' demographic traits should depend on its position along the fast-slow continuum. In particular, it is expected that NAO would have a higher impact on recruitment than on adult survival in slow species, while the opposite pattern is expected occur in fast species. To test these predictions, we used long-term capture-recapture datasets (more than 15,000 individuals marked from 1965 to 2015) on different surveyed populations of three amphibian species in Western Europe: Triturus cristatus, Bombina variegata, and Salamandra salamandra. Despite substantial intraspecific variation, our study revealed that these three species differ in their position on a slow-fast gradient of pace of life. Our results also suggest that the differences in life history tactics influence amphibian responses to NAO fluctuations: Adult survival was most affected by the NAO in the species with the fastest pace of life (T. cristatus), whereas recruitment was most impacted in species with a slower pace of life (B. variegata and S. salamandra). In the context of climate change, our findings suggest that the capacity of organisms to deal with future changes in NAO values could be closely linked to their position on the fast-slow continuum.

Food availability as a major driver in the evolution of life-history strategies of sibling species

Life‐history theory predicts trade‐offs between reproductive and survival traits such that different strategies or environmental constraints may yield comparable lifetime reproductive success among conspecifics. Food availability is one of the most important environmental factors shaping developmental processes. It notably affects key life‐history components such as reproduction and survival prospect. We investigated whether food resource availability could also operate as an ultimate driver of life‐history strategy variation between species. During 13 years, we marked and recaptured young and adult sibling mouse‐eared bats (Myotis myotis and Myotis blythii) at sympatric colonial sites. We tested whether distinct, species‐specific trophic niches and food availability patterns may drive interspecific differences in key life‐history components such as age at first reproduction and survival. We took advantage of a quasi‐experimental setting in which prey availability for the two species varies between years (pulse vs. nonpulse resource years), modeling mark‐recapture data for demographic comparisons. Prey availability dictated both adult survival and age at first reproduction. The bat species facing a more abundant and predictable food supply early in the season started its reproductive life earlier and showed a lower adult survival probability than the species subjected to more limited and less predictable food supply, while lifetime reproductive success was comparable in both species. The observed life‐history trade‐off indicates that temporal patterns in food availability can drive evolutionary divergence in life‐history strategies among sympatric sibling species.

The role of abiotic and biotic cues in burrow habitat selection by juvenile crayfish

Environmental cues contain critical information for individuals while searching for mates and suitable habitat. Crayfish have well-developed chemosensory abilities for detecting environmental cues in water; much less is known about these abilities on land. The Devil crayfish (Cambarus diogenes) is a burrowing crayfish often found in dense floodplain colonies as adults. Juveniles however are released in surface water and must navigate overland to burrow. Previous work demonstrates juveniles use cues from conspecific adults, and to a lesser extent, soil cues, for burrow site selection. Using mesocosms, we build on this by examining burrowing cues associated with (1) congeneric adults, (2) excavated burrow material and (3) other juveniles. In contrast to conspecific adults, cues provided by congeneric adults did not override cues associated with soil type. Similarly, juveniles burrowed closer to conspecific adult burrow mounds than to congeneric and human-built mounds. Juveniles also showed significant grouping behaviour in the absence of all other cues. These results suggest juvenile crayfish integrate multiple terrestrial cues for burrow site selection.

Integrating copper toxicity and climate change to understand extinction risk to two species of pond-breeding anurans

Chemical contamination is often suggested as an important contributing factor to amphibian population declines, but direct links are rarely reported. Population modeling provides a quantitative method to integrate toxicity data with demographic data to understand the long-term effects of contaminants on population persistence. In this study we use laboratory-derived embryo and larval toxicity data for two anuran species to investigate the potential for toxicity to contribute to population declines. We use the southern toad (Anaxyrus terrestris) and the southern leopard frog (Lithobates sphenocephalus) as model species to investigate copper (Cu) toxicity. We use matrix models to project populations through time and quantify extinction risk (the probability of quasi-extinction in 35 yr). Life-history parameters for toads and frogs were obtained from previously published literature or unpublished data from a long-term (>35 yr) data set. In addition to Cu toxicity, we investigate the role of climate change on amphibian populations by including the probability of early pond drying that results in catastrophic reproductive failure (CRF, i.e., complete mortality of all larval individuals). Our models indicate that CRF is an important parameter for both species as both were unable to persist when CRF probability was >50% for toads or 40% for frogs. Copper toxicity alone did not result in significant effects on extinction risk unless toxicity was very high (>50% reduction in survival parameters). For toads, Cu toxicity and high probability of CRF both resulted in high extinction risk but no synergistic (or greater than additive) effects between the two stressors occurred. For leopard frogs, in the absence of CRF survival was high even under Cu toxicity, but with CRF Cu toxicity increased extinction risk. Our analyses highlight the importance of considering multiple stressors as well as species differences in response to those stressors. Our models were consistently most sensitive to juvenile and adult survival, further suggesting the importance of terrestrial stages to population persistence. Future models will incorporate multiple wetlands with different combinations of stressors to understand if our results for a single wetland result in a population sink within the landscape.

Demographic responses to weather fluctuations are context dependent in a long-lived amphibian

Weather fluctuations have been demonstrated to affect demographic traits in many species. In long-lived organisms, their impact on adult survival might be buffered by the evolution of traits that reduce variation in interannual adult survival. For example, skipping breeding is an effective behavioral mechanism that may limit yearly variation in adult survival when harsh weather conditions occur; however, this in turn would likely lead to strong variation in recruitment. Yet, only a few studies to date have examined the impact of weather variation on survival, recruitment and breeding probability simultaneously in different populations of the same species. To fill this gap, we studied the impact of spring temperatures and spring rainfall on survival, on reproductive skipping behavior and on recruitment in five populations of a long-lived amphibian, the yellow-bellied toad (Bombina variegata). Based on capture-recapture data, our findings demonstrate that survival depends on interactions between age, population and weather variation. Varying weather conditions in the spring result in strong variation in the survival of immature toads, whereas they have little effect on adult toads. Breeding probability depends on both the individual's previous reproductive status and on the weather conditions during the current breeding season, leading to high interannual variation in recruitment. Crucially, we found that the impact of weather variation on demographic traits is largely context dependent and may thus differ sharply between populations. Our results suggest that studies predicting the impact of climate change on population dynamics should be taken with caution when the relationship between climate and demographic traits is established using only one population or few populations. We therefore highly recommend further research that includes surveys replicated in a substantial number of populations to account for context-dependent variation in demographic processes.

Density regulation in toad populations (Epidalea calamita, Bufotes viridis) by differential winter survival of juveniles

The size of amphibian populations varies considerably between years, so that systematic trends in dynamics are difficult to detect. Informed conservation management of presumably declining populations requires the identification of the most sensitive life stage. In temperate-zone anurans there is growing evidence that juveniles hibernating for the first time suffer from substantial winter losses. In two syntopic toads (Epidalea calamita, Bufotes viridis) we monitored survival of such juveniles during four consecutive winters in the natural habitat and in four temperature treatments (3°, 5 °C, 10°/15 °C or 20 °C, natural light-dark cycle) in temperature-controlled chambers during winter. Specifically, we tested the hypotheses that (1) winter mortality of juvenile toads which hibernate for the first time in their life is an important component of population dynamics, and that (2) mortality rates differed between the two species. Parameters quantified were size-dependent winter mortality and body condition of pre- and post-hibernating juveniles. Field data provided evidence for the important role of winter mortality of first-hibernators in population dynamics. Choice of hibernacula differed in E. calamita between small and medium-sized individuals and also between the two species suggesting distinct mortality risks. The inability of small E. calamita to reach frost-proof hibernacula by burrowing, and the exposure of small B. viridis to predators are the most probable causes of size-assortative winter mortality. In conclusion, E. calamita juveniles may benefit from rising average winter temperatures in the future by decreased risk of freezing to death, whereas predator-caused winter mortality of B. viridis juveniles will also depend on the effects of climate warming on predator phenology.