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Abstract Ongoing amphibian population declines are caused by factors such as climate change, habitat destruction, pollution and infectious diseases not limited to chytridiomycosis. Unfortunately, action is taken against these factors once population collapses are underway. To avoid these post hoc responses, wildlife endocrinology aims to analyse physiological mediators that predict future population declines to inform wildlife management. Mediators typically investigated are stress hormones known as glucocorticoids, which are produced by the Hypothalamus—Pituitary—Interrenal axis (HPI axis). The HPI axis is the part of the endocrine system that helps amphibians cope with stress. Chronic increases in glucocorticoids due to stress can lead to immune dysfunction, which makes amphibians more susceptible to infectious diseases. Despite this predictive potential of glucocorticoids, interpretation of glucocorticoid data is confounded by sampling design and type. Glucocorticoid monitoring classically involves blood sampling, which is not widely applicable in amphibians as some are too small or delicate to sample, and repeated samples are often valued. To address this, we tried to validate skin swabbing via corticosterone (CORT) and adrenocorticotropin hormone (ACTH) injections in adults of two amphibian species: Eastern red-spotted newts, Notophthalmus viridescens viridescens, with natural skin infections with Batrachochytrium dendrobatidis (Bd) upon collection in the field, and Northern leopard frogs, Rana (Lithobates) pipiens, raised in captivity and naïve to Bd exposure. Further, we determined the predictive potential of skin glucocorticoids on Bd load in the field via correlations in Eastern red-spotted newts. We found that hormones present in the skin are not related to the HPI axis and poorly predict infection load; however, skin hormone levels strongly predicted survival in captivity. Although skin swabbing is not a valid method to monitor HPI axis function in these species, the hormones present in the skin still play important roles in organismal physiology under stressful conditions relevant to wildlife managers. 

Abstract Human‐induced climate change, land use changes, and urbanization are predicted to dramatically impact landscape hydrology, which can have devastating impacts on aquatic organisms. For amphibians that rely on aquatic environments to breed and develop, it is essential to understand how the larval environment impacts development, condition, and performance later in life. Two important predicted impacts of climate change, urbanization, and land use changes are reduced hydroperiod and variable larval density. Here, we explored how larval density and hydroperiod affect development, morphology, physiology, and immune defenses at metamorphosis and 35 days post‐metamorphosis in the frogRana pipiens. We found that high‐density larval conditions had a large negative impact on development and morphology, which resulted in longer larval periods, reduced likelihood of metamorphosis, smaller size at metamorphosis, shorter femur to body length ratio, and reduced microbiome species evenness compared with animals that developed in low‐density conditions. However, animals from the high‐density treatment experienced compensatory growth post‐metamorphosis, demonstrating accelerated growth in body size and relative femur length compared with animals from the low‐density treatments, despite not “catching‐up” in size. We also observed an increase in relative gut length and relative liver size in animals that had developed in the high‐density treatment than those in the low‐density treatment, as well as higher bacterial killing ability, and greater jump distances relative to their leg length across different temperatures. Finally, metabolic rate was higher overall but especially at higher test temperatures for animals that developed under high‐density conditions, indicating that these animals may expend more energy in response to acute temperature changes. While the effects of climate change have direct negative effects on larval development and metamorphosis, animals can increase growth rate post‐metamorphosis; however, that compensatory growth might come at a cost and reduce their ability to cope with further environmental change such as increased temperatures. 

Abstract Vast alteration of the biosphere by humans is causing a sixth mass extinction, driven in part by an increase in infectious diseases. The emergence of the lethal fungal pathogenBatrachochytrium dendrobatidis(Bd) has devastated global amphibian biodiversity. Given the lack of any broadly applicable methods to reverse these impacts, the future of many amphibians appears grim. The Sierra Nevada yellow-legged frog (Rana sierrae) is highly susceptible to Bd infection and mostR. sierraepopulations are extirpated following disease outbreaks. However, some populations persist and eventually recover, and frogs in these recovering populations have increased resistance against infection. Here, we conduct a 15-year reintroduction study and show that frogs collected from recovering populations and reintroduced to vacant habitats can reestablish populations despite the presence of Bd. In addition, the likelihood of establishment is influenced by site, cohort, and frog attributes. Results from viability modeling suggest that many reintroduced populations have a low probability of extinction over 50 years. These results provide a rare example of how reintroduction of resistant individuals can allow the landscape-scale recovery of disease-impacted species, and have broad implications for amphibians and other taxa that are threatened with extinction by novel pathogens. 

ABSTRACT Studying declining and rare species is inherently challenging, particularly when the cause of rarity is emerging infectious diseases (EIDs). Tracking changes in the distribution of pathogens that cause EIDs, and the species made scarce by them, is necessary for conservation efforts, but it is often a time and resource intensive task. Here, we demonstrate how using environmental DNA (eDNA) to detect rare species—and the pathogens that threaten them—can be a powerful tool to understand disease dynamics and develop effective conservation strategies. Amphibian populations around the world have undergone rapid declines and extinctions due to the emerging fungal pathogen,Batrachochytrium dendrobatidis(Bd). We developed and validated a qPCR assay using eDNA sampling methods for some of the most imperiled amphibian species, harlequin frogs (Atelopus varius,Atelopus zeteki,andAtelopus chiriquiensis), and applied this assay in concert with a standard qPCR assay forBdin rainforest streams of Panamá. We confirmed the presence ofAtelopusat sampling locations across three regions. In addition, we used genomic analysis of eDNA samples to show thatBdin Panamá falls within the Global Panzootic Lineage, a lineage associated with disease‐induced declines. We detectedBdDNA in most of our historic sites, and its concentration in water samples correlated with stream characteristics and the pathogen load of the local amphibian community. These results suggest that some populations ofAtelopuspersist in their historic localities. They also show how eDNA analysis can be effectively used for monitoring species presence, pathogen concentrations, and the distribution and spread of pathogen lineages. EIDs are a growing threat to endangered species around the world. Simultaneous detection of rare and declining host species and their pathogens with eDNA will help to provide key insights for effective conservation management. 

Synopsis Intraspecific variation can be as great as variation across species, but the role of intraspecific variation in driving local and large-scale patterns is often overlooked, particularly in the field of thermal biology. In amphibians, which depend on environmental conditions and behavior to regulate body temperature, recognizing intraspecific thermal trait variation is essential to comprehensively understanding how global change impacts populations. Here, we examine the drivers of micro- and macrogeographical intraspecific thermal trait variation in amphibians. At the local scale, intraspecific variation can arise via changes in ontogeny, body size, and between the sexes, and developmental plasticity, acclimation, and maternal effects may modulate predictions of amphibian performance under future climate scenarios. At the macrogeographic scale, local adaptation in thermal traits may occur along latitudinal and elevational gradients, with seasonality and range-edge dynamics likely playing important roles in patterns that may impact future persistence. We also discuss the importance of considering disease as a factor affecting intraspecific variation in thermal traits and population resilience to climate change, given the impact of pathogens on thermal preferences and critical thermal limits of hosts. Finally, we make recommendations for future work in this area. Ultimately, our goal is to demonstrate why it is important for researchers to consider intraspecific variation to determine the resilience of amphibians to global change. 

Synopsis Antimicrobial peptides (AMPs) play a fundamental role in the innate defense against microbial pathogens, as well as other immune and non-immune functions. Their role in amphibian skin defense against the pathogenic fungus Batrachochytrium dendrobatidis (Bd) is exemplified by experiments in which depletion of host’s stored AMPs increases mortality from infection. Yet, the question remains whether there are generalizable patterns of negative or positive correlations between stored AMP defenses and the probability of infection or infection intensity across populations and species. This study aims to expand on prior field studies of AMP quantities and compositions by correlating stored defenses with an estimated risk of Bd exposure (prevalence and mean infection intensity in each survey) in five locations across the United States and a total of three species. In all locations, known AMPs correlated with the ability of recovered secretions to inhibit Bd in vitro. We found that stored AMP defenses were generally unrelated to Bd infection except in one location where the relative intensity of known AMPs was lower in secretions from infected frogs. In all other locations, known AMP relative intensities were higher in infected frogs. Stored peptide quantity was either positively or negatively correlated with Bd exposure risk. Thus, future experiments coupled with organismal modeling can elucidate whether Bd infection affects secretion/synthesis and will provide insight into how to interpret amphibian ecoimmunology studies of AMPs. We also demonstrate that future AMP isolating and sequencing studies can focus efforts by correlating mass spectrometry peaks to inhibitory capacity using linear decomposition modeling. 

Synopsis Examples of resilience in nature give us hope amid a growing biodiversity crisis. While resilience has many definitions across disciplines, here I discuss resilience as the ability to continue to adapt and persist. Naturally, as biologists, we seek to uncover the underlying mechanisms that can help us explain the secrets of resilience across scales, from individuals to species to ecosystems and beyond. Perhaps we also ponder what the secrets to resilience are in our own lives, in our own research practices, and academic communities. In this paper, I highlight insights gained through studies of amphibian resilience following a global disease outbreak to uncover shared patterns and processes linked to resilience across amphibian communities. I also reflect on how classical resilience heuristics could be more broadly applied to these processes and to our own academic communities. Focusing on the amphibian systems that I have worked in—the Golden Frogs of Panama (Atelopus zeteki/varius) and the Mountain Yellow-Legged Frogs of California (Rana muscosa/sierrae)—I highlight shared and unique characteristics of resilience across scales and systems and discuss how these relate to adaptive renewal cycles. Reflecting on this work and previous resilience scholarship, I also offer my own thoughts about academia and consider what lessons we could take from mapping our own adaptive trajectories and addressing threats to our own community resilience. 

Abstract The onset of global climate change has led to abnormal rainfall patterns, disrupting associations between wildlife and their symbiotic microorganisms. We monitored a population of pumpkin toadlets and their skin bacteria in the Brazilian Atlantic Forest during a drought. Given the recognized ability of some amphibian skin bacteria to inhibit the widespread fungal pathogenBatrachochytrium dendrobatidis(Bd), we investigated links between skin microbiome health, susceptibility to Bd and host mortality during a die‐off event. We found that rainfall deficit was an indirect predictor of Bd loads through microbiome disruption, while its direct effect on Bd was weak. The microbiome was characterized by fewer putative Bd‐inhibitory bacteria following the drought, which points to a one‐month lagged effect of drought on the microbiome that may have increased toadlet susceptibility to Bd. Our study underscores the capacity of rainfall variability to disturb complex host–microbiome interactions and alter wildlife disease dynamics. 

Abstract Variable harlequin frogsAtelopus variushave declined significantly throughout their range as a result of infection with the fungal pathogenBatrachochytrium dendrobatidis(Bd). The Panama Amphibian Rescue and Conservation Project maintains an ex situ population of this Critically Endangered species. We conducted a release trial with surplus captive-bredA. variusindividuals to improve our ability to monitor frog populations post-release, observe dispersal patterns after freeing them into the wild and learn about threats to released frogs, as well as to determine whether natural skin toxin defences of frogs could be restored inside mesocosms in the wild and to compare Bd dynamics in natural amphibian communities at the release site vs a non-release site. The 458 released frogs dispersed rapidly and were difficult to re-encounter unless they carried a radio transmitter. No frog was seen after 36 days following release. Thirty frogs were fitted with radio transmitters and only half were trackable by day 10. Tetrodotoxin was not detected in the skins of the frogs inside mesocosms for up to 79 days. Bd loads in other species present at sites were high prior to release and decreased over time in a pattern probably driven by weather. No differences were observed in Bd prevalence between the release and non-release sites. This trial showed that refinements of our methods and approaches are required to study captiveAtelopusfrogs released into wild conditions. We recommend continuing release trials of captive-bred frogs with post-release monitoring methods, using an adaptive management framework to advance the field of amphibian reintroduction ecology. 

Synopsis Recent strides toward improving diversity, equity, and inclusion (DEI) in field biology present a unique opportunity for transdisciplinary exploration of the impacts and state of a topic that has remained hereto largely underexplored and under-discussed in the academic setting. Within current literature, themes of racial and gender inequity, power imbalances, unsafe environments, and underdeveloped infrastructure and resources are widespread. Thus, we organized a symposium that addressed these compelling issues in field biology DEI through a multitude of experiential and academic lenses. This article will orient the reader to the special issue and offer summative goals and outcomes of the symposium that can provide tangible steps toward creating meaningful improvements in the state of DEI and safety in field settings.