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Quantifying how contaminants change across life cycles of species who undergo metamorphosis is critical to assessing risk to organisms and their consumers. Pond-breeding amphibians can dominate aquatic animal biomass as larvae and are terrestrial prey as metamorphs and adults. Thus, amphibians can be vectors of mercury accumulation in both aquatic and terrestrial food webs. However, it is still unclear how mercury concentrations are affected by exogenous (e.g., habitat or diet) vs. endogenous factors (e.g., catabolism during hibernation) as amphibians undergo large diet shifts and periods of fasting during ontogeny. We measured total mercury (THg), methylmercury (MeHg), and isotopic compositions (?13C, ?15N) in boreal chorus frogs (Pseudacris maculata) across five life stages in two metapopulations in Colorado, USA. We found large differences in MeHg concentrations and percent of THg as MeHg among life stages. Frog MeHg concentrations spiked after metamorphosis and hibernation coinciding with the most energetically demanding stages of their life cycle. Transitions among life stages led to large step changes in mercury concentrations – the endogenous processes of metamorphosis and hibernation biomagnified MeHg, decoupling isotopic compositions and MeHg concentrations. These step changes are not often considered in conventional expectations of how food web processes predict trophic transfer, accumulation, and transport of contaminants. ?

1. One of the primary ways in which climate change will impact coastal freshwater wetlands is through changes in the frequency, intensity, timing, and distribution of extreme weather events. Disentangling the direct and indirect mechanisms of population- and community-level responses to extreme events is vital to predicting how species composition of coastal wetlands will change under future conditions.

2. We extended static structural equation modeling approaches to incorporate system dynamics in a multi-year multispecies occupancy model to quantify the effects of extreme weather events on a coastal freshwater wetland system.

3. We used data from an 8-year study (2009 to 2016) on St. Marks National Wildlife Refuge in Florida, USA, to quantify species-specific and community-level changes in amphibian and fish occupancy associated with two flooding events in 2012 and 2013. We examine how physical changes to the landscape, including potential changes in salinity and increased wetland connectivity, may have contributed to or exacerbated the effects of these extreme weather events on the biota of isolated coastal wetlands.

4. We provide evidence that the primary effects of flooding on the amphibian community were through indirect mechanisms via changes in the composition of the sympatric fish community that may have had lethal (i.e., through direct predation) or non-lethal (i.e., through direct or indirect competitive interactions) effects. In addition, we shown that amphibian species differed in their sensitivity to direct flooding effects and indirect changes in the fish community and wetland specific conductance, which led to variable responses across the community. These effects led to the overall decline in amphibian species richness from 2009 to 2016, suggesting that wetland-breeding amphibian communities on St. Marks may not be resilient to predicted changes in coastal disturbance regimes as a result of climate change.

5. Understanding both direct and indirect effects, as well as species interactions, is important for predicting the effects of a changing climate on individual species, communities, and ecosystems.

1. Understanding the causes of population variation in host response to disease, and the mechanisms of persistence, can serve as vital information for species conservation. One such mechanism of population persistence that has gained support is the demographic process of compensatory recruitment. Host populations may persist by increasing recruitment to compensate for reduced survival due to infection, thus limiting the negative effects of the disease on population trajectories. However, high elevation populations are inherently vulnerable to stochastic processes and may be limited in their ability to exhibit compensatory recruitment relative to lower elevation populations.
2. We use long-term mark-recapture data from five populations of boreal toads (Anaxyrus boreas boreas ), across an elevational gradient in Colorado, before and after pathogen arrival to assess whether populations can persist with Batrachochytrium dendrobatidis (Bd) via compensatory recruitment.
3. Prior to pathogen arrival, we found a life history tradeoff between survival and recruitment across elevations, where high elevation toads have high survival but lower recruitment and vice versa at lower elevations.
4. Pathogen arrival had a strong negative effect on apparent annual survival and recruitment leading to negative population growth rates and dramatically reduced host abundances. The data did not support the occurrence of compensatory recruitment.
5. Synthesis and applications. Our unique dataset indicates that demographic responses to pathogens may be environmentally (i.e., elevationally) context-dependent and highlights the value of long-term monitoring. We recommend that practitioners verify that potential persistence mechanisms occur across multiple populations and relevant environmental gradients to counter any assumptions of the mechanism existing species-wide. Quantifying variation in population responses to disease will aid in understanding the bounds of such persistence mechanisms and identify particularly vulnerable populations where mechanisms are non-existent.

Many studies have noted apparent differences in microbes associated with animals reared in captivity compared to their wild counterparts. Few studies have examined how microbes change when animals are reintroduced to the wild after being reared in captivity. As captive assurance populations and reintroduction programs increase, a better understanding of how microbial symbionts respond during animal translocations is critical. We examined changes in microbes of boreal toads (Anaxyrus boreas) after reintroduction to the wild following captive rearing. Boreal toads, a long-lived high elevation species, are endangered in Colorado primarily due to chytridiomycosis. Previous studies demonstrate that developmental life stage of boreal toads is an important factor in their microbiomes such that microbiomes change over the course of development. i) comparisons of the skin, mouth, and gut bacteria of boreal toads across four developmental life stages in captivity and the wild, ii) pre-metamorphic tadpole skin bacteria before and after reintroduction to the wild, and iii) adult skin bacteria during reintroduction to the wild. We used barcoded amplicon sequencing of the 16S small subunit of the rRNA gene on the Illumina MiSeq platform to characterize the bacterial communities. We demonstrated that differences occur across the skin gut and mouth microbes in captive versus wild boreal toads, and that the degree of difference depend on developmental stage. Skin bacteria from captive versus wild tadpoles were more similar relative to post-metamorphic life stages. When captive reared tadpoles were introduced to a wild site, their skin bacteria changed to mirror wild boreal toads within weeks. Similarly, the microbiome of reintroduced adult boreal toads also shifted to mirror wild-type microbes. Our results indicate that the microbial signature of boreal toads reared in captivity does not persist after release into natural habitat. The relationship between changing microbes and host health is not well understood for the majority of animal species but is an important part of wildlife conservation.

Insights from conservation genomics have dramatically improved recovery plans for numerous endangered species. However, most taxa have yet to benefit from the full application of genomic technologies. The mountain yellow-legged frog species complex, Rana muscosa and Rana sierrae, inhabits the Sierra Nevada mountains and Transverse/Peninsular Ranges of California and Nevada. Both species have declined precipitously throughout their historical distributions. Conservation management plans outline extensive ongoing recovery efforts but are still based on the genetic structure determined primarily using a single mitochondrial sequence. Our study used two different sequencing strategies – amplicon sequencing and exome capture – to refine our understanding of the population genetics of these imperiled amphibians. We used buccal swabs, museum tissue samples, and archived skin swabs to genotype frog populations across their range. Using the amplicon sequencing and exome capture datasets separately and combined, we document five major genetic clusters. Notably, we found evidence supporting previous species boundaries within Kings Canyon National Park with some exceptions at individual sites. Though we see evidence of genetic clustering, especially in the R. muscosa clade, we also found evidence of some admixture across cluster boundaries in the R. sierrae clade, suggesting a stepping-stone model of population structure. We also find that the southern R. muscosa cluster had large runs of homozygosity and the lowest overall heterozygosity of any of the clusters, consistent with previous reports of marked declines in this area. Overall, our results clarify management unit designations across the range of an endangered species and highlight the importance of sampling the entire range of a species, even when collecting genome-scale data.

Climate change is an increasingly important driver of biodiversity loss. The ectothermic nature of amphibians may make them particularly sensitive to changes in normal temperature and precipitation regimes, exacerbating global declines from other threats. In this study, we used large-scale citizen science data from the eastern half of the United States to assess how variation in winter severity influenced occupancy dynamics of 11 anuran species. We found that most species had increased occupancy in years with greater than average snow cover and warmer than average mean winter temperatures. Surprisingly, we found that climatic conditions in winter affected occupancy dynamics of both spring and summer breeding species, indicating that changing winter conditions may have consequences for anuran species with varying life history characteristics. As the climate continues to change, expected reductions in snowpack may act as an additional stressor on already declining anuran populations, while milder winters may improve overwinter survival for some species.

Increasing temperatures and climate-driven disturbances like wildfire are a growing threat to many species,
including cold-water specialists. Montane areas and cold streams are often considered climate refugia that buffer
communities against change. However, climate refugia are often species-specific, and despite growing awareness
that life histories and habitat requirements shape responses to change, small or non-game species are often
under-represented in monitoring and planning programs. A recent study in Montana, USA, revealed much larger
warming-related declines in occupancy for small, non-game slimy sculpin (Cottus cognatus) between 1993 and
1995 and 2011–2013 than for two socially valued salmonid fishes that shape regional conservation efforts. To
broaden insight into climate change vulnerabilities of headwater stream communities, we analyzed data for
Rocky Mountain tailed frogs (Ascaphus montanus) that were collected during those same electrofishing surveys
for fishes from 241 stream reaches. Tailed frogs occupy small, cold streams and have several life-history traits
that make them sensitive to environmental change. We used a Bayesian framework to estimate occupancy,
colonization, and extinction dynamics relative to forest canopy, estimated stream temperature, and wildfire
effects. Tailed frog occupancy decreased by 19 % from 1993 to 1995 to 2011–2013. Changes in occupancy were
linked with increased extinction and reduced colonization where there were fire-driven reductions in canopy
cover, and reduced colonization of stream reaches that warmed on average 0.8 ?C during the study. Our results
highlight extensive extirpations for oft-overlooked species and emphasize the importance of including species
with diverse habitat requirements and life histories in conservation planning.

Invasive species and emerging infectious diseases are two of the greatest
threats to biodiversity. American Bullfrogs (Rana [Lithobates] catesbeiana),
which have been introduced to many parts of the world, are often linked with
declines in native amphibians via predation and the spread of emerging pathogens
such as amphibian chytrid fungus (Batrachochytrium dendrobatidis [Bd])
and ranaviruses. Although many studies have investigated the potential role of
bullfrogs in the decline of native amphibians, analyses that account for shared
habitat affinities and imperfect detection have found limited support for
clear effects. Similarly, the role of bullfrogs in shaping the patch-level distribution
of pathogens is unclear. We used eDNA methods to sample 233 sites in the southwestern USA and Sonora, Mexico (2016–2018) to estimate how
the presence of bullfrogs affects the occurrence of four native amphibians,
Bd, and ranaviruses. Based on two-species, dominant-subordinate occupancy
models fitted in a Bayesian context, federally threatened Chiricahua Leopard
Frogs (Rana chiricahuensis) and Western Tiger Salamanders (Ambystoma
mavortium) were eight times (32% vs. 4%) and two times (36% vs. 18%), respectively,
less likely to occur at sites where bullfrogs occurred. Evidence for the
negative effects of bullfrogs on Lowland Leopard Frogs (Rana yavapaiensis)
and Northern Leopard Frogs (Rana pipiens) was less clear, possibly because of
smaller numbers of sites where these native species still occurred and because
bullfrogs often occur at lower densities in streams, the primary habitat for
Lowland Leopard Frogs. At the community level, Bd was most likely to occur
where bullfrogs co-occurred with native amphibians, which could increase the
risk to native species. Ranaviruses were estimated to occur at 33% of bullfrogonly
sites, 10% of sites where bullfrogs and native amphibians co-occurred,
and only 3% of sites where only native amphibians occurred. Of the 85 sites
where we did not detect any of the five target amphibian species, we also did
not detect Bd or ranaviruses; this suggests other hosts do not drive the distribution
of these pathogens in our study area. Our results provide landscape-scale
evidence that bullfrogs reduce the occurrence of native amphibians and
increase the occurrence of pathogens, information that can clarify risks and
aid the prioritization of conservation actions.

Rockland habitat in South Florida, USA, is a threatened ecosystem that has been lost, fragmented, or degraded because of urbanization or other anthropogenic disturbance. Furthermore, low-lying islands and coastal areas are experiencing sea-level rise (SLR) and an increased frequency and intensity of tidal flooding, putting rockland habitats there at increasing risk of ecological change. We evaluated changes in the extent of rockland habitat under various scenarios of future SLR, tidal flooding, and human development for two endemic state-listed threatened species of snakes, the Rim Rock Crowned Snake (Tantilla oolitica) and the Key Ring-necked Snake (Diadophis punctatus acricus). Both snakes are restricted to South Florida. We used recent and historical species’ records to determine each species’ habitat range. We then estimated the extent of future habitat loss due to SLR and continued human development, as well as degradation of the remaining habitat. We also asked whether the future potential drivers of habitat loss and degradation differ between the two species and across their habitat ranges. We predicted that saltwater intrusion could negatively affect rocklands by 2050, resulting in degradation of 80% of the existing habitat because of an anticipated 42 cm of SLR. Moreover, short-term stochastic events such as storm surge and high tides will increasingly saturate the root zone of rockland vegetation before complete inundation. Most of the rockland habitat used by these two species of snakes will be inundated by 2080. Sea level rise will likely change current rocklands into more halophytic habitat (mangrove or salt marsh wetland) within 50 to 60 years. As much as 47% of rockland habitat will be lost due to human development by 2030. Therefore, immediate mitigation actions may be needed to conserve specialist species within rockland habitat that is threatened by human activities and climate change.

Small population sizes and no possibility of metapopulation rescue put narrowly distributed endemic species under elevated risk of extinction from anthropogenic change. Desert spring wetlands host many endemic species that require aquatic habitat and are isolated by the surrounding xeric terrestrial habitat. Aims. We sought to model the occupancy dynamics of the Dixie Valley toad (Anaxyrus williamsi), a recently described species endemic to a small desert spring wetland complex in Nevada, USA. Methods. We divided the species’ range into 20 m × 20 m cells and surveyed for Dixie Valley toads at 60 cells during six primary periods from 2018 to 2021, following an occupancy study design. We analysed our survey data by using a multi-state dynamic occupancy model to estimate the probability of adult occurrence, colonisation, site survival, and larval occurrence and the relationship of each to environmental covariates. Key results. The detection probabilities of adult and larval toads were affected by survey length and time of day. Adult Dixie Valley toads were widely distributed, with detections in 75% of surveyed cells at some point during the 3-year study, whereas larvae were observed only in 20% of cells during the study. Dixie Valley toad larvae were more likely to occur in cells far from spring heads with a high coverage of surface water, low emergent vegetation cover, and water temperatures between 20°C and 28°C. Adult toads were more likely to occur in cells with a greater coverage of surface water and water depth >10 cm. Cells with more emergent vegetation cover and surface water were more likely to be colonised by adult toads. Conclusions. Our results showed that Dixie Valley toads are highly dependent on surface water in both spring and autumn. Adults and larvae require different environmental conditions, with larvae occurring farther from spring heads and in fewer cells. Implications. Disturbances to the hydrology of the desert spring wetlands in Dixie Valley could threaten the persistence of this narrowly distributed toad.

Maintenance of genetic diversity at adaptive loci may facilitate invasions by non-native species by allowing populations to adapt to novel environments, despite the loss of diversity at neutral loci that typically occurs during founder events. To evaluate this prediction, we compared genetic diversity at major histocompatibility complex (MHC) and cytochrome b (cytb) loci from 20 populations of the American bullfrog (Rana catesbeiana) across the invasive and native ranges in North America and quantified the presence of the pathogen Batrachochytrium dendrobatidis (Bd). Compared to native populations, invasive populations had significantly higher Bd prevalence and intensity, significantly higher pairwise MHC and cytb FST, and significantly lower cytb diversity, but maintained similar levels of MHC diversity. The two most common MHC alleles (LiCA_B and Rapi_33) were associated with a significant decreased risk of Bd infection, and we detected positive selection acting on four peptide binding residues. Phylogenetic analysis suggested invasive populations likely arose from a single founding population in the American Midwest with a possible subsequent invasion in the northwest. Overall, our study suggests that the maintenance of diversity at adaptive loci may contribute to invasion success and highlights the importance of quantifying diversity at functional loci to assess the evolutionary potential of invasive populations.

Recent work has shown that many amphibians are biofluorescent. Biofluorescence describes an organism’s ability to absorb visible and ultraviolet light and re-emit it at a lower energy level (e.g., blue light re-emitted as green fluorescence). However, the function of fluorescence in amphibians is unclear. We observed paedomorphic western tiger salamanders at Lily Lake in Rocky Mountain National Park and obtained the first images recorded at this park of biofluorescence in these animals in response to blue light.

Species with especially close dependence on the environment to meet physiological requirements, such as ectotherms, are highly susceptible to the impacts of climate change. Climate change is occurring rapidly in the Subarctic and Arctic, but there is limited knowledge on ectotherm physiology in these landscapes. We investigated how environmental conditions and habitat characteristics influence the physiological conditions and habitat use of wood frogs (Rana sylvatica, LeConte 1825) in a Subarctic landscape near Churchill, Manitoba (Canada). We used plaster models to estimate water loss rates and surface body temperatures among different habitat types and at specific locations used by radio-tracked frogs. Water loss (R^2 = 0.67) and surface temperature (R^2 = 0.80) of plaster models was similar to that of live frogs. Model-based water loss rates were greater in tundra habitat than in boreal forest and ecotone habitat. Habitat use of wood frogs was strongly tied with available surface moisture and decreased water loss rates that were observed with plaster models. Environmental conditions, such as wind speed and ground temperature, explained 58% and 91% of the variation in water balance and temperature of plaster models. Maintaining physiological conditions may be challenging for semi-aquatic ectotherms in environments vulnerable to future climate change. The ability to predict physiological conditions based on environmental conditions, as demonstrated in our study, can help understand how wildlife will respond to climatic changes.

Studying the movements of organisms that live underground for at least a portion of their life history is challenging, given
the state of current technology. Passive integrated transponders (PIT tags) provide a way to individually identify and, more recently,
study the movement of smaller animals, including those that make subterranean movements. However, there are widespread
assumptions of the use of PIT tags that remain problematic. We tested the effects of PIT-tag implantation on growth and survival, along
with the effects of electromagnetic fields for reading PIT tags on behavior, of the smallest salamander that has been PIT-tagged: the Red-
Backed Salamander. We found no effect of PIT tags on growth or survival. Using a mesocosm experiment, we also found that
electromagnetic effects associated with reading PIT tags, had no effect on salamander behavior. Further, we describe a novel PIT antenna
and soil mesocosm experimental arena for studying belowground movements of woodland salamanders. Collectively, these studies
suggest that the use of PIT tags do not influence the growth, survival, or behavior of Red-Backed Salamanders. Given the challenges of
studying salamanders that live underground and the impending changes in climate and landscapes, this research suggests that PIT tags
remain a viable tool for studying the movement ecology of salamanders under global change.

Shasta salamanders (collectively, Hydromantes samweli, H. shastae, and H. wintu; hereafter Shasta salamander) are endemic to northern California in the general vicinity of Shasta Lake reservoir. Although generally associated with limestone, they have repeatedly been found in association with other habitats, calling into question the distribution of the species complex. Further limiting our knowledge of the species’ distributions is that they are only active or available for sampling on the soil surface for a small portion of the year, and detection probabilities for the species have never been estimated. We developed and implemented a survey protocol designed to estimate detection, availability, and occurrence probabilities from December 2019 through March 2020. We provide inference on Shasta salamander occurrence in portions of their range that have received little survey effort. We found that Shasta salamander occurrence was positively associated with the percent cover of embedded rock, and their availability (i.e., probability of being active on the soil surface during sampling) was positively related to relative humidity. The probability of occurrence of Shasta salamanders in our study area was low, and our winter-to-spring survey protocol was effective for estimating detection, availability, and occurrence probabilities in the study area and at specific sites. We suggest that conducting replicate surveys that quantify animal availability and detection probabilities will facilitate a better understanding of the habitat associations of Shasta salamanders and other rare species that might often be unavailable for detection

The lingual lure of Alligator Snapping Turtles, Macrochelys Gray, are believed to be the only prey-capturing lures within the mouths of modern reptiles. To date, no formal assessment of lure condition in Alligator Snapping Turtles has been published, and few researchers record lure data. Herein, we report damaged or missing lures from 25 Alligator Snapping Turtles (7 adults, 18 juveniles) from a sample of more than 2,000 lure assessments in 4 states, indicating this is a rare occurrence. We also describe lingual lure color observed in these assessments and introduce standardized terminology and color categories. We suggest researchers record data on the condition and coloration of the lingual lure to further our understanding of this ecological and evolutionary adaptation.

Introduction piece for a special issue.

news story

Prolonged drought due to climate change has negatively impacted amphibians in southern California, U.S.A. Due to the severity and length of the current drought,
agencies and researchers had growing concern for the persistence of the arroyo toad (Anaxyrus californicus), an endangered endemic amphibian in this region. Range-wide surveys for this species had not been conducted for at least 20 years. In 2017–2020, we conducted collaborative surveys for arroyo toads at historical locations. We surveyed 88 of the 115 total sites having historical records and confirmed that the arroyo toad is currently extant in at least 61 of 88 sites and 20 of 25 historically occupied watersheds. We did not detect toads at almost a third of the surveyed sites but did detect toads at 18 of 19 specific sites delineated in the 1999 Recovery Plan to meet one of four downlisting criteria. Arroyo toads are estimated to live 7–8 years, making populations susceptible to prolonged drought. Drought is estimated to increase in frequency and duration with climate change. Mitigation strategies for drought impacts, invasive aquatic species, altered flow regimes, and other anthropogenic effects could be the most beneficial strategies for toad conservation and may also provide simultaneous benefits to several other native species that share the same habitat.

The endangered mountain yellow-legged frog (Rana muscosa) has been reduced to <10 isolated populations in the wild. Due to frequent catastrophic events (floods, droughts, wildfires), the recent dynamics of these populations have been erratic, making the future of the species highly uncertain. In 2018, a recovery plan was developed to improve the species status by reducing the impacts of various threats (predation, disease, habitat destruction), as well as reinforcing wild populations through the reintroduction of captive-bred frogs. The short-term goal stated in this plan was to reach a minimum of 20 populations of 50 adults each (hereafter, the 20/50 target), before the species can be considered for downlisting from the U.S. Endangered Species Act. However, there is no guarantee that this 20/50 target will be sufficient to ensure the species persistence in the long run. Using 19 years of mark-recapture data, we estimated populations' demographic trends and assessed the viability of R. muscosa from a starting state of 20 populations of 50 adults each (i.e., the downlisting criteria). Our results reveal that, from this 20/50 state, the species has high chances of persistence only at a short time horizon (50 years). Moreover, >80% of populations would be extinct 50 years later. Therefore, the species will not be able to persist without implementation of the reintroduction program. We found that it is more important to increase the number of suitable sites occupied by R. muscosa than to simply reinforce or augment existing populations. Expanding the current distribution by establishing new populations at suitable sites, even after the “20 populations” mark has been reached, would increase the likelihood of the species' persistence in the longer term.