Recent Products

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. ?

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.

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

Introduction piece for a special issue.

news story