Pseudacris Maculata Research Articles

Isolation and Characterization of a Frog Virus 3 Strain from a Wood Frog (Rana sylvatica) in Wood Buffalo National Park.

Members of the Iridoviridae family, genus Ranavirus, represent a group of globally emerging pathogens of ecological and economic importance. In 2017, an amphibian die-off of wood frogs (Rana sylvatica) and boreal chorus frogs (Pseudacris maculata) was reported in Wood Buffalo National Park, Canada. Isolation and complete genomic sequencing of the tissues of a wood frog revealed the presence of a frog virus 3 (FV3)-like isolate, Rana sylvatica ranavirus (RSR), with a genome size of 105,895 base pairs, 97 predicted open reading frames (ORFs) bearing sequence similarity to FV3 (99.98%) and a FV3-like isolate from a spotted salamander in Maine (SSME; 99.64%). Despite high sequence similarity, RSR had a unique genomic composition containing ORFs specific to either FV3 or SSME. In addition, RSR had a unique 13 amino acid insertion in ORF 49/50L. No differences were found in the in vitro growth kinetics of FV3, SSME, and RSR; however, genomic differences between these isolates were in non-core genes, implicated in nucleic acid metabolism and immune evasion. This study highlights the importance of viral isolation and complete genomic analysis as these not only provide information on ranavirus spatial distribution but may elucidate genomic factors contributing to host tropism and pathogenicity.

Rearing density and food variety impact growth, development, and survival of larvae in the declining amphibian, Pseudacris maculata.

Boreal chorus frogs (Pseudacris maculata Agassiz 1850) are a widespread amphibian in North America, but several populations are in decline. Specifically, we are developing captive breeding and reintroduction methods for the Great Lakes/St. Lawrence-Canadian Shield population. Here we present the effects of tadpole density, food variety, and addition of supplemental minerals to rearing water on the growth, development, and survival during the larval and metamorph/juvenile stages. We conducted two experiments using a factorial design. We found that low tadpole density (1vs. 2 tadpoles/L) and high food variety (fivefood items vs. three food items) significantly increased tadpole body length and Gosner stage after 2 weeks (p < .001), increased survival to metamorphosis (p < .001), decreased time to metamorphosis (p < .001), and increased weight after metamorphosis (p < .001). On average, tadpoles in the high density/low food treatment, compared to the low density/high food, were 25% smaller after 2 weeks, had 3.9× lower survival to metamorphosis, took 1.25× longer to reach metamorphosis, and weighed 1.5× less after metamorphosis. In contrast, neither density (0.5vs. 1 tadpole/L) nor mineral supplemented water affected growth and development, but tadpole survival was higher at 1 tadpole/L. Our findings demonstrate the feasibility of rearing boreal chorus frogs in captivity and provide guidelines for rearing this and similar species in a laboratory environment.

Environmental DNA surveys can underestimate amphibian occupancy and overestimate detection probability: implications for practice

AbstractEnvironmental DNA analysis of water samples has recently emerged as a powerful tool for studying the distribution, ecology, and conservation of many amphibian species. Validating efficacy through comparison with established methods of detection is important for any new method. We used multi‐method and single‐method occupancy models to explore the effectiveness of 3 techniques for detecting northern leopard frogs (Lithobates pipiens) and boreal chorus frogs (Pseudacris maculata). We conducted surveys using automated recording units, environmental DNA sampling, and visual encounter surveys in spring (30 Apr–3 Jun) and summer (23 Jul–27 Aug) of 2014 at 68 sites in southern Alberta, Canada. The multi‐method analysis incorporated data from all 3 survey methods while accounting for the lack of independence of detections within a sampling occasion, and we compared this to single‐method analyses to explore occupancy biases associated with each method and differences in method‐specific detection probability. Occupancy and detection probabilities estimated from environmental DNA analyses were biased for northern leopard frogs, overestimating probability of detection and underestimating occupancy. We could not assess bias for boreal chorus frogs because of overdispersion present in in the models. Although no single covariate explained this bias, it was ameliorated (albeit by reducing precision) by including a raw visual count of individuals as a proxy for abundance during the breeding but not the post‐metamorphic season. These results emphasize the need for careful consideration of temporal and spatial aspects of sampling design, conducting pilot studies, and external validation of eDNA‐only occupancy monitoring schemes prior to widespread implementation.

Complex Life Histories Alter Patterns of Mercury Exposure and Accumulation in a Pond-Breeding Amphibian.

Quantifying how contaminants change across life cycles of species that undergo metamorphosis is critical to assessing organismal risk, particularly for consumers. Pond-breeding amphibians can dominate aquatic animal biomass as larvae and are terrestrial prey as juveniles and adults. Thus, amphibians can be vectors of mercury exposure 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 (δ 13C, δ15N) in boreal chorus frogs (Pseudacris maculata) across five life stages in two Colorado (USA) metapopulations. We found large differences in concentrations and percent MeHg (of THg) among life stages. Frog MeHg concentrations peaked during metamorphosis and hibernation coinciding with the most energetically demanding life cycle stages. Indeed, life history transitions involving periods of fasting coupled with high metabolic demands led to large increases in mercury concentrations. The endogenous processes of metamorphosis and hibernation resulted in MeHg bioamplification, thus decoupling it from the light isotopic proxies of diet and trophic position. These step changes are not often considered in conventional expectations of how MeHg concentrations within organisms are assessed.

Provisioning of breeding habitat by beaver and beaver dam analogue complexes within the Great Salt Lake catchment

Abstract Beaver are ecosystem engineers capable of converting free‐flowing lotic habitats into a series of lentic ponds, thereby enhancing the wetland area of a riverscape. Process‐based riverscape restoration using beaver reintroductions and mimicry (beaver dam analogues, BDAs) are increasingly used to restore functions, the provisioning of services, and improve the resiliency of ecosystems across North America and Europe. Beaver can create breeding habitat for a wide range of species within the highly imperilled class Amphibia by increasing wetland area, increasing emergent vegetation, prolonging wetland hydroperiod, and creating deep ponds. However, it remains unclear whether BDAs are creating suitable breeding habitat for amphibians by adequately emulating crucial ecosystem processes. We investigated the relationships between beaver dam and BDA complexes with amphibian breeding occupancy across four catchments feeding the Great Salt Lake, U.S.A. We surveyed 24 beaver dam complexes and nine BDA complexes during the 2019–2021 breeding seasons with varying levels of water availability. We compared environmental characteristics between beaver and BDA complexes, including elevation, depth, and fish relative abundance among others. We then used occupancy models to evaluate factors affecting breeding occupancy of the most frequently encountered amphibian species, barred tiger salamanders (Ambystoma mavortium). Without accounting for imperfect detection, at natural beaver ponds we recorded barred tiger salamanders in 58% of sites, boreal chorus frogs (Pseduarcris maculata) at 17% of sites, and northern leopard frogs (Lithobates pipens) at 4% of sites. Tiger salamanders were the only amphibian found at BDA sites, occupying 11% of those sites. We found that beaver complexes had 3 times less fish relative abundance, were 250m higher in elevation, 32 years older, and 0.43 m deeper than their BDA counterparts. Meanwhile, emergent vegetation height, water temperature, and hydroperiod demonstrated no significant differences between site types. BDAs modified ecosystem processes in a way that only partially replicated modifications by natural beaver dams. Occupancy models suggested that fish relative abundance, altitude, age, and being at the top of the drainage network were the most important variables for predicting tiger salamander breeding occupancy. Overall occupancy rate of tiger salamanders was 60%, while BDA complexes had a modelled occupancy rate of 14% compared to 78% in natural beaver complexes. Survey year did not appear to be an important factor in tiger salamander occupancy despite varying levels of water availability. Beaver and BDA complexes located near the top of their effective drainage or tributary junctions appeared to support amphibian along with fish species, thus boosting local diversity relative to a stream with only fish species. We therefore suggest future beaver restoration efforts target the top of effective drainages to benift both taxa. Overall, we found that while BDAs have the capacity to provide amphibian habitat, their younger age and higher fish abundance may explain why they are less effective than natural dams. Managers should therefore consider that the effects of restoration with BDAs may not be immediate, and future maintenance may be required.

Assessing the breeding phenology of a threatened frog species using eDNA and automatic acoustic monitoring.

Climate change has driven shifts in breeding phenology of many amphibians, causing phenological mismatches (e.g., predator-prey interactions), and potentially population declines. Collecting data with high spatiotemporal sensitivity on hibernation emergence and breeding times can inform conservation best practices. However, monitoring the phenology of amphibians can be challenging because of their cryptic nature over much of their life cycle. Moreover, most salamanders and caecilians do not produce conspicuous breeding calls like frogs and toads do, presenting additional monitoring challenges. In this study, we designed and evaluated the performance of an environmental DNA (eDNA) droplet digital PCR (ddPCR) assay as a non-invasive tool to assess the breeding phenology of a Western Chorus Frog population (Pseudacris maculata mitotype) in Eastern Ontario and compared eDNA detection patterns to hourly automatic acoustic monitoring. For two eDNA samples with strong PCR inhibition, we tested three methods to diminish the effect of inhibitors: diluting eDNA samples, adding bovine serum albumin to PCR reactions, and purifying eDNA using a commercial clean-up kit. We recorded the first male calling when the focal marsh was still largely frozen. Chorus frog eDNA was detected on April 6th, 6 days after acoustic monitoring revealed this first calling male, but only 2 days after males attained higher chorus activity. eDNA signals were detected at more sampling locales within the marsh and eDNA concentrations increased as more males participated in the chorus, suggesting that eDNA may be a reasonable proxy for calling assemblage size. Internal positive control revealed strong inhibition in some samples, limiting detection probability and quantification accuracy in ddPCR. We found diluting samples was the most effective in reducing inhibition and improving eDNA quantification. Altogether, our results showed that eDNA ddPCR signals lagged behind male chorusing by a few days; thus, acoustic monitoring is preferable if the desire is to document the onset of male chorusing. However, eDNA may be an effective, non-invasive monitoring tool for amphibians that do not call and may provide a useful complement to automated acoustic recording. We found inhibition patterns were heterogeneous across time and space and we demonstrate that an internal positive control should always be included to assess inhibition for eDNA ddPCR signal interpretations.

Do Not Croak! A Story of Surviving Yellowstone’s Frigid Winters

Have you ever wondered how “cold-blooded” animals like amphibians (frogs, toads, and salamanders) survive the winter without fur or feathers to keep them warm? Yellowstone National Park’s amphibians have found ways to stay alive during the cold winter months. These animals have evolved various coping strategies, from burrowing underground, to living in ponds, to tolerating the freezing of much of the water in their bodies. This article will explore the strategies used by several amphibians to survive the winter, including strategies used by the boreal chorus frog, Columbia spotted frog, western toad, and western tiger salamander. Understanding the diverse ways that amphibians survive in their winter habitats helps scientists to recommend ways to protect those habitats, to ensure that amphibians have healthy places to live and reproduce.

Chloride Toxicity to Native Freshwater Species in Natural and Reconstituted Prairie Pothole Waters.

Oil and gas extraction in the Prairie Pothole Region (PPR) of the northern USA has resulted in elevated chloride concentrations in ground and surface water due to widespread contamination with highly saline produced water, or brine. The toxicity of chloride is poorly understood in the high hardness waters characteristic of the region. We evaluated the toxicity of chloride to two endemic species, Daphnia magna (water flea) and Lemna gibba (duckweed), exposed in field-collected waters (hardness ~ 3000mg/L as CaCO3) and reconstituted waters (hardness 370mg/L as CaCO3) intended to mimic PPR background waters. We also investigated the role of chloride in the toxicity of water reconstituted to mimic legacy brine-contaminated wetlands, using two populations of native Pseudacris maculata (Boreal Chorus Frog). Chloride toxicity was similar in field-collected and reconstituted waters for both D. magna (LC50s 3070-3788mg Cl-1/L) and L. gibba (IC50s 2441-2887). Although hardness can ameliorate chloride toxicity at low to high hardness, we did not observe additional protection as hardness increased from 370 to ~ 3000mg/L. In P. maculata exposures, chloride did not fully explain toxicity. Chloride sensitivity also differed between populations, with mortality at 2000mg Cl-/L in one population but not the other, and population-specific growth responses. Overall, these results (1) document toxicity to native species at chloride concentrations occurring in the PPR, (2) indicate that very high hardness in the region's waters may not provide additional protection against chloride and (3) highlight challenges of brine investigations, including whether surrogate study populations are representative of local populations.

Ranavirus Amplification in Low-Diversity Amphibian Communities.

In an era where emerging infectious diseases are a serious threat to biodiversity, epidemiological patterns need to be identified, particularly the complex mechanisms driving the dynamics of multi-host pathogens in natural communities. Many amphibian species have faced unprecedented population declines associated with diseases. Yet, specific processes shaping host-pathogen relationships within and among communities for amphibian pathogens such as ranaviruses (RV) remain poorly understood. To address this gap, we conducted a comprehensive study of RV in low-diversity amphibian communities in north-western Canada to assess the effects of biotic factors (species identity, species richness, abundance) and abiotic factors (conductivity, pH) on the pathogen prevalence and viral loads. Across 2 years and 18 sites, with communities of up to three hosts (wood frog, Rana sylvatica; boreal chorus frog, Pseudacris maculata; Canadian toad, Anaxyrus hemiophrys), we observed that RV prevalence nearly doubled with each additional species in a community, suggesting an amplification effect in aquatic, as well as terrestrial life-history stages. Infection intensity among infected wood frogs and boreal chorus frogs also significantly increased with an increase in species richness. Interestingly, we did not observe any effects of host abundance or abiotic factors, highlighting the importance of including host identity and species richness when investigating multi-host pathogens. Ultimately, only such a comprehensive approach can improve our understanding of complex and often highly context-dependent host-pathogen interactions.

Modelling physiological costs to assess impacts of climate change on amphibians in Yellowstone National Park, U.S.A

Amphibians are vital elements of ecosystems, serving as predator and prey. Their biphasic nature makes them dependent on aquatic and terrestrial habitats; as wet-skinned ectotherms, they are vulnerable to a range of environmental threats, including climate change. Yellowstone National Park (YNP) is becoming warmer and drier, and some wetlands important to amphibians have diminished. Continued climate change is predicted to reduce snowpack, soil moisture, and forest cover. We used data from models of future climate and vegetation cover to mechanistically model how climate change might affect the movements of Western Toads (Anaxyrus boreas) across the landscape of three test areas in YNP for the years 2050 and 2090, compared to 2000 as a baseline. Least-cost path analysis produced mixed results: for 2050 and 2090, physiological costs of movement increased in one test area and decreased in another; they were mixed in the third. These changes generally reflect the preference by toads for more open forests. Estimating costs for other species of YNP amphibians produced more negative results. For Columbia Spotted Frogs (Rana luteiventris) and Boreal Chorus Frogs (Pseudacris maculata) (both more aquatic and less adapted to terrestrial habitats), movement costs increased by about 2–15X. Reduced frequency or duration of rain events might limit the nocturnal movements of Western Tiger Salamanders (Ambystoma mavortium). Climate change may not have negative impacts on all amphibians throughout YNP, but increased movement costs for terrestrial habitats will accentuate effects of drying wetlands in at least parts of YNP. Land management actions that preserve habitat structure of both forest and low shrub cover may help mitigate continued drying conditions of climate change.

Distribution of the boreal chorus frog (Pseudacris maculata) in an urban environment using environmental DNA

AbstractThe boreal chorus frog (Pseudacris maculata) is at risk of extinction in parts of its range in Canada. Our objectives were to quantify the influence of local and landscape characteristics on the occurrence of the species in wetlands in southern Québec. We hypothesized that site occupancy depends on local characteristics and landscape characteristics contributing to site connectivity. We developed an environmental DNA (eDNA) method to detect the species and compared the detection probability of this method to traditional call surveys. We collected water samples from a total of 180 sites (90 in 2017, 110 in 2018), whereas we surveyed a subset of 63 sites using both eDNA and call surveys in 2018. Site occupancy varied across years, but was higher in sites where the species had been previously detected during the last 12 years by other studies. Site occupancy did not vary with other local and landscape characteristics, in part due to an apparent decrease in the number of sites occupied by the species since the last 12 years. Detection probability via eDNA (0.81; 95% CI: [0.31; 0.98]) did not differ from that of call surveys (0.62; 95% CI: [0.25; 0.89]). To identify the optimal sampling period for the boreal chorus frog, future studies should estimate the detection probability of eDNA during the breeding season and the larval development period of the species.

Comparative Effects of Energy-Related Saline Wastewaters and Sodium Chloride on Hatching, Survival, and Fitness-Associated Traits of Two Amphibian Species.

Salinity (sodium chloride [NaCl]) is a prevalent and persistent contaminant that negatively affects freshwater ecosystems. Although most studies focus on effects of salinity from road salts (primarily NaCl), high-salinity wastewaters from energy extraction (wastewaters) could be more harmful because they contain NaCl and other toxic components. Many amphibians are sensitive to salinity, and their eggs are thought to be the most sensitive life-history stage. However, there are few investigations with salinity that include eggs and larvae sequentially in long-term exposures. We investigated the relative effects of wastewaters from a large energy reserve, the Williston Basin (USA), and NaCl on northern leopard (Rana pipiens) and boreal chorus (Pseudacris maculata) frogs. We exposed eggs and tracked responses through larval stages (for 24 days). Wastewaters and NaCl caused similar reductions in hatching and larval survival, growth, development, and activity, while also increasing deformities. Chorus frog eggs and larvae were more sensitive to salinity than leopard frogs, suggesting species-specific responses. Contrary to previous studies, eggs of both species were less sensitive to salinity than larvae. Our ecologically relevant exposures suggest that accumulating effects can reduce survival relative to starting experiments with unexposed larvae. Alternatively, egg casings of some species may provide some protection against salinity. Notably, effects of wastewaters on amphibians were predominantly due to NaCl rather than other components. Therefore, findings from studies with other sources of increased salinity (e.g., road salts) could guide management of wastewater-contaminated ecosystems, and vice versa, to mitigate effects of salinization. Environ Toxicol Chem 2021;40:3137-3147. © 2021 SETAC.

Amphibian population responses to mitigation: Relative importance of wetland age and design

Wetland creation is a common practice to mitigate for the loss of natural wetlands. However, there is still uncertainty about how effectively created wetlands replace habitat provided by natural wetlands. This uncertainty is due in part because post-construction monitoring of biological communities, and vertebrates especially, is rare and typically short-term (<5 years). We estimated occupancy of 4 amphibian species in 8 created mitigation wetlands, 7 impacted wetlands, and 7 reference wetlands in the Greater Yellowstone Ecosystem in Wyoming, USA. Mitigation wetlands were created to replace wetland habitat that was lost during road construction and ranged in age from 1 to 10 years when sampled. Impacted wetlands were natural wetlands partially filled by road construction and were adjacent to a highway. We sampled for amphibian larvae during 6 summers from 2013 to 2020 and used multi-species occupancy models that estimated detection and occupancy of each of 4 amphibian species to determine how amphibian responses changed over time, especially in mitigation wetlands. Occupancy did not differ between impacted and reference wetlands for any of the 4 amphibian species. Western Toads (Anaxyrus boreas) were most common (although briefly) in created wetlands, and occupancy of Columbia Spotted Frogs (Rana luteiventris), Western Tiger Salamanders (Ambystoma mavortium), and Boreal Chorus Frogs (Pseudacris maculata) was lower in created wetlands than in impacted or reference wetlands. Individual wetland area was positively associated with occupancy for all 4 species and wetland vegetation cover was positively associated with Boreal Chorus Frog and Columbia Spotted Frog occupancy; these results emphasize the importance of design characteristics when planning mitigation wetlands. The link between wetland age and occupancy was complex and included threshold and quadratic relationships for three of the four species, but only Boreal Chorus Frog occupancy was still increasing slowly at the end of our study. Our results indicate created wetlands did not attain the suitability of impacted and natural wetlands for local amphibians, even several years after construction. The complex relationships between wetland age and species-specific occupancy illustrate the importance of long-term monitoring in describing population responses to the construction of wetlands as mitigation for wetland loss.

Ecological causes of fluctuating natural selection on habitat choice in an amphibian.

We estimated natural selection targeting three traits related to habitat choice in a frog (Pseudacris maculata) breeding in pools on the rocky shores of Isle Royale, Michigan, over 16 years. Our aim was to identify the form and ecological causes of annual variation in directional and correlational selection as expressed in the survival and growth of tadpoles. We found directional selection favoring early breeding, but pool choice was under weak stabilizing selection. However, the form of stabilizing selection and the position of the optimum trait value shifted among years with the severity of disturbance and the intensity of biotic interactions. In years when wave wash and pool desiccation were severe, selection shifted to favor tadpoles in habitats where these risks were less pronounced. If predatory dragonfly larvae were abundant, selection favored tadpoles in small pools where dragonflies did not occur. When intraspecific competition was strong, selection favored early broods within a broader range of pool types. The agents of selection in this study—biotic interactions and disturbance—are common to many ecological systems and frequently exhibit temporal variation; this suggests that fluctuating selection may be widespread in natural populations.

Automated detection of frog calls and choruses by pulse repetition rate.

Anurans (frogs and toads) are among the most globally threatened taxonomic groups. Successful conservation of anurans will rely on improved data on the status and changes in local populations, particularly for rare and threatened species. Automated sensors, such as acoustic recorders, have the potential to provide such data by massively increasing the spatial and temporal scale of population sampling efforts. Analyzing such data sets will require robust and efficient tools that can automatically identify the presence of a species in audio recordings. Like bats and birds, many anuran species produce distinct vocalizations that can be captured by autonomous acoustic recorders and represent excellent candidates for automated recognition. However, in contrast to birds and bats, effective automated acoustic recognition tools for anurans are not yet widely available. An effective automated call‐recognition method for anurans must be robust to the challenges of real‐world field data and should not require extensive labeled data sets. We devised a vocalization identification tool that classifies anuran vocalizations in audio recordings based on their periodic structure: the repeat interval‐based bioacoustic identification tool (RIBBIT). We applied RIBBIT to field recordings to study the boreal chorus frog (Pseudacris maculata) of temperate North American grasslands and the critically endangered variable harlequin frog (Atelopus varius) of tropical Central American rainforests. The tool accurately identified boreal chorus frogs, even when they vocalized in heavily overlapping choruses and identified variable harlequin frog vocalizations at a field site where it had been very rarely encountered in visual surveys. Using a few simple parameters, RIBBIT can detect any vocalization with a periodic structure, including those of many anurans, insects, birds, and mammals. We provide open‐source implementations of RIBBIT in Python and R to support its use for other taxa and communities.

Batrachochytrium dendrobatidis in Kansas

Batrachochytrium dendrobatidis (Bd) has been implicated in the decline of amphibians worldwide and was first noted in Kansas in 2014 in Kingman and Sedgwick Counties. The objectives of this study were to further assess the presence of Bd throughout the state. We sampled anurans at 25 locations throughout the state and Bd was detected at six sample locations: Marais Des Cygnes National Wildlife Refuge, Farlington Fish Hatchery, Hadley Ranch, Quivira National Wildlife Refuge, Tuttle Creek Wildlife Area, and Jamestown Wildlife Area and across six species: Gray Treefrogs, Boreal Chorus Frogs, Woodhouse's Toads, Blanchard's Cricket Frogs, Plains Leopard Frogs, and American Bullfrogs. We did not find evidence that Bd was negatively impacting populations at this time. We suggest continued monitoring of anuran populations to ensure population survival into the future.

Drivers of distributions and niches of North American cold‐adapted amphibians: evaluating both climate and land use

Species distribution estimates are often used to understand the niche of a species; however, these are often based solely on climatic predictors. When the influences of biotic factors are ignored, erroneous inferences about range and niche may be made. We aimed to integrate climate data with a unique set of available land cover and land use data for the six cold-adapted amphibians of North America (Ambystoma macrodactylum, Anaxyrus hemiophrys, Anaxyrus boreas, Pseudacris maculata, Rana sylvatica, Rana luteiventris) to determine the relative importance of climate and non-climate drivers through the use of ecological niche models for present-day range estimates. We compared climate-only, land use-only, and combination models of climate and land use, derived from two different model selection techniques, to determine which was most likely to drive current distributions of cold-adapted amphibian species. Land use layers included land cover type, human population, vegetation type, ecoregion, and the overall human footprint. The most supported models included both climate and land use, with climate and human footprint variables having the highest permutation importance and percent contribution. Models that incorporated climate and land use data performed best as measured with AIC and AUC, although qualitatively most underestimated the northern range edge, implying potential sampling bias or locations of reduced habitat quality for these species in the northern area of the ranges. There were small differences in overall combination models dependent on the method of model selection. The overall effect sizes of landscape factors within the combination models were small except for one landscape feature: human footprint, which incorporated multiple aspects of anthropogenic change on the landscape, including human population density, travel access, and agricultural impact. This aspect of the landscape was just as important as climate, and counter to what we expected, the association was mostly positive, with a negative response only occurring at very high levels. This highlights the importance of moving beyond climate only species range estimates as land cover, specifically human impact, may be driving the patterns of species' ranges.

Evaluating corticosterone as a biomarker for amphibians exposed to increased salinity and ambient corticosterone.

Physiological biomarkers are commonly used to assess the health of taxa exposed to natural and anthropogenic stressors. Glucocorticoid (GC) hormones are often used as indicators of physiological stress in wildlife because they affect growth, reproduction and survival. Increased salinity from human activities negatively influences amphibians and their corticosterone (CORT; the main amphibian GC) physiology; therefore, CORT could be a useful biomarker. We evaluated whether waterborne CORT could serve as a biomarker of salt stress for three free-living amphibian species that vary in their sensitivity to salinity: boreal chorus frogs (Pseudacris maculata), northern leopard frogs (Rana pipiens) and barred tiger salamanders (Ambystoma mavortium). Across a gradient of contamination from energy-related saline wastewaters, we tested the effects of salinity on baseline and stress-induced waterborne CORT of larvae. Stress-induced, but not baseline, CORT of leopard frogs increased with increasing salinity. Salinity was not associated with baseline or stress-induced CORT of chorus frogs or tiger salamanders. Associations between CORT and salinity were also not related to species-specific sensitivities to salinity. However, we detected background environmental CORT (ambient CORT) in all wetlands and spatial variation was high within and among wetlands. Higher ambient CORT was associated with lower waterborne CORT of larvae in wetlands. Therefore, ambient CORT likely confounded associations between waterborne CORT and salinity in our analysis and possibly influenced physiology of larvae. We hypothesize that larvae may passively take up CORT from their environment and downregulate endogenous CORT. Although effects of some hormones (e.g. oestrogen) and endocrine disruptors on aquatic organisms are well described, studies investigating the occurrence and effects of ambient CORT are limited. We provide suggestions to improve collection methods, reduce variability and avoid confounding effects of ambient CORT. By making changes to methodology, waterborne CORT could still be a promising, non-invasive conservation tool to evaluate effects of salinity on amphibians.

Density Dependence and Adult Survival Drive Dynamics in Two High Elevation Amphibian Populations

Amphibian conservation has progressed from the identification of declines to mitigation, but efforts are hampered by the lack of nuanced information about the effects of environmental characteristics and stressors on mechanistic processes of population regulation. Challenges include a paucity of long-term data and scant information about the relative roles of extrinsic (e.g., weather) and intrinsic (e.g., density dependence) factors. We used a Bayesian formulation of an open population capture-recapture model and &gt;30 years of data to examine intrinsic and extrinsic factors regulating two adult boreal chorus frogs (Pseudacris maculata) populations. We modelled population growth rate and apparent survival directly, assessed their temporal variability, and derived estimates of recruitment. Populations were relatively stable (geometric mean population growth rate &gt;1) and regulated by negative density dependence (i.e., higher population sizes reduced population growth rate). In the smaller population, density dependence also acted on adult survival. In the larger population, higher population growth was associated with warmer autumns. Survival estimates ranged from 0.30–0.87, per-capita recruitment was &lt;1 in most years, and mean seniority probability was &gt;0.50, suggesting adult survival is more important to population growth than recruitment. Our analysis indicates density dependence is a primary driver of population dynamics for P. maculata adults.

Assessing ecological and environmental influences on boreal chorus frog (Pseudacris maculata) spring calling phenology using multimodal passive monitoring technologies

Although anuran reproductive behavior follows a phenological pattern, environmental factors may influence the timing of anuran activity. To characterize the spring calling phenology of Pseudacris maculata (boreal chorus frog) we installed acoustic recorders during three spring breeding seasons (2015–2017) within wet meadow and forested slough habitats in central Nebraska near the Platte River. The recorders were paired with time-lapse camera systems that were used to measure vegetation change and wet meadow inundation. We examined the relationship between environmental variables, including temperature, precipitation, and hydropattern, and P. maculata calling activity using random forest models. Calling activity exhibited diel and seasonal variation with differences observed between habitats. Hourly call activity was highest between 20:00 and 01:00, with diurnal and sometimes near-continuous calling observed at the wet meadow but not at the forested slough. Random forest models explained 73% of calling activity variance at the wet meadow and 45% at the forested slough, suggesting additional factors, such as predation, may be influential at the forested slough, as it exhibited near permanent hydrology. P. maculata was predicted to increase chorusing at the 70th day of the year at the wet meadow but not until the 100th at the forested slough. When average air temperatures exceeded 5 °C, calling activity was predicted to increase at both wetlands, and calling declined below this temperature. Hydropattern and weekly precipitation accumulation were important predictors of P. maculata calling activity. Our findings highlight the importance of climatic factors such as temperature and precipitation regimes, in addition to habitat conditions such as water-availability, on P. maculata calling activity. Furthermore, this study demonstrates the utility of multimodal passive monitoring technologies, including both visual and auditory tools, for understanding the environmental factors that influence biological activity. Multimodal approaches can be especially useful for documenting and measuring vocal-taxa diversity, activity, and drivers of change.