Altitudinal distribution of chytrid (Batrachochytrium dendrobatidis) infection in subtropical Australian frogs

UV exposure causes energy trade-offs leading to increased chytrid fungus susceptibility in green tree frog larvae

Levels of ultraviolet (UV) radiation have increased in many parts of the world due to the anthropogenic destruction of the ozone layer. UV radiation is a potent immunosuppressant and can increase the susceptibility of animal hosts to pathogens. UV radiation can directly alter immune function via immunosuppression and photoimmunotolerance; however, UV may also influence pathogen defences by affecting the distribution of energy resources among competing physiological processes. Both defence against UV damage and repair of incurred damage, as well as the maintenance of immune defences and responding to an immune challenge, are energetically expensive. These competing demands for finite energy resources could trade off against one another, resulting in sub-optimal performance in one or both processes. We examined the potential for a disease-related energy trade-off in green tree frog (Litoria caerulea) larvae. Larvae were reared under high- or low-UV conditions for 12 weeks during which time we measured growth rates, metabolic rate and susceptibility to the amphibian fungal pathogen, Batrachochytrium dendrobatidis (Bd). We found that larvae exposed to high levels of UV radiation had higher rates of energy expenditure than those exposed to low UV levels; however, UV exposure did not affect growth rates or developmental timings. Larvae exposed to high UV radiation also experienced greater Bd infection rates and carried a higher infection burden than those not exposed to elevated UV radiation. We propose that the increased energetic costs of responding to UV radiation were traded off against immune defences to protect larval growth rates. These findings have important implications for the aetiology of some Bd-associated amphibian declines, particularly in montane environments where Bd infections are most severe and where UV levels are highest.

Prevalence of Batrachochytrium dendrobatidis in Amphibians From 2000 to 2021: A Global Systematic Review and Meta-Analysis

Chytridiomycosis is an amphibian fungal disease caused by Batrachochytrium dendrobatidis (Bd), which has caused large-scale death and population declines on several continents around the world. To determine the current status of Bd infection in amphibians, we conducted a global meta-analysis. Using PubMed, ScienceDirect, SpringerLink, China National Knowledge Infrastructure (CNKI) and Wanfang database searches, we retrieved a total of 111 articles from 2000 to 2021. Based on these, we estimated the Bd prevalence to be 18.54% (95% CI: 13.76–20.52) in current extent amphibians. Among these populations, the prevalence of Bd in Asia was the lowest at 7.88% (95% CI: 1.92–8.71). Further, no Bd infection was found in Vietnam. However, the prevalence of Bd in Oceania was the highest at 36.34% (95% CI: 11.31–46.52). The Bd prevalence in Venezuela was as high as 49.77% (95% CI: 45.92–53.62). After 2009, the global Bd prevalence decreased to 18.91% (95% CI: 13.23–21.56). The prevalence of Bd in epizootic populations was significantly higher than enzootic populations. The highest prevalence of Bd was detected with real-time PCR at 20.11% (95% CI: 13.12–21.38). The prevalence of Bd in frogs was the highest at 20.04% (95% CI: 13.52–21.71), and this different host was statistically significant (P < 0.05). At the same time, we analyzed the geographic factors (longitude, latitude, elevation, rainfall and temperature) that impacted the fungal prevalence in amphibians. Our meta-analysis revealed that factors including region, disease dynamic, detection method, host and climate may be sources of the observed heterogeneity. These results indicate that chytridiomycosis was a consistent threat to amphibians from 2000 to 2021. Based on different habitat types and geographical conditions, we recommend formulating corresponding control plans and adopting reasonable and efficient biological or chemical methods to reduce the severity of such diseases.

Microplastics increase susceptibility of amphibian larvae to the chytrid fungus Batrachochytrium dendrobatidis

Microplastics (MPs), a new class of pollutants that pose a threat to aquatic biodiversity, are of increasing global concern. In tandem, the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) causing the disease chytridiomycosis is emerging worldwide as a major stressor to amphibians. We here assess whether synergies exist between this infectious disease and MP pollution by mimicking natural contact of a highly susceptible species (midwife toads, Alytes obstetricans) with a Bd-infected reservoir species (fire salamanders, Salamandra salamandra) in the presence and absence of MPs. We found that MP ingestion increases the burden of infection by Bd in a dose-dependent manner. However, MPs accumulated to a greater extent in amphibians that were not exposed to Bd, likely due to Bd-damaged tadpole mouthparts interfering with MP ingestion. Our experimental approach showed compelling interactions between two emergent processes, chytridiomycosis and MP pollution, necessitating further research into potential synergies between these biotic and abiotic threats to amphibians.

Bioclimatic and anthropogenic variables shape the occurrence of Batrachochytrium dendrobatidis over a large latitudinal gradient

Amphibian chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), has caused the greatest known loss of biodiversity due to an infectious disease. We used Bd infection data from quantitative real-time PCR (qPCR) assays of amphibian skin swabs collected across Chile during 2008-2018 to model Bd occurrence with the aim to determine bioclimatic and anthropogenic variables associated with Bd infection. Also, we used Bd presence/absence records to identify geographical Bd high-risk areas and compare Bd prevalence and infection loads between amphibian families, ecoregions, and host ecology. Data comprised 4155 Bd-specific qPCR assays from 162 locations across a latitudinal gradient of 3700 km (18º to 51ºS). Results showed a significant clustering of Bd associated with urban centres and anthropogenically highly disturbed ecosystems in central-south Chile. Both Bd prevalence and Bd infection loads were higher in aquatic than terrestrial amphibian species. Our model indicated positive associations of Bd prevalence with altitude, temperature, precipitation and human-modified landscapes. Also, we found that macroscale drivers, such as land use change and climate, shape the occurrence of Bd at the landscape level. Our study provides with new evidence that can improve the effectiveness of strategies to mitigate biodiversity loss due to amphibian chytridiomycosis.

Living with the pathogenic chytrid fungus: Exploring mechanisms of coexistence in the harlequin toad Atelopus cruciger

Chytridiomycosis, a disease caused by the fungus Batrachochytrium dendrobatidis (Bd), has been linked with the disappearance of amphibian populations worldwide. Harlequin toads (Atelopus) are among the most severely impacted genera. Two species are already considered extinct and most of the others are at high risk of extinction. The recent rediscovery of harlequin toad populations coexisting with Bd suggest that the pathogen can maintain enzootic cycles at some locations. The mechanisms promoting coexistence, however, are not well understood. We explore the dynamics of Bd infection in harlequin toads by modeling a two-stage host population with transmission through environmental reservoirs. Simulations showed that variations in the recruitment of adults and the persistence of zoospores in the environment were more likely to drive shifts between extinction and coexistence than changes in the vulnerability of toads to infection with Bd. These findings highlight the need to identify mechanisms for assuring adult recruitment or minimizing transmission from potential reservoirs, biotic or abiotic, in recovering populations.

TEMPERATURE AS A DRIVER OF THE PATHOGENICITY AND VIRULENCE OF AMPHIBIAN CHYTRID FUNGUS BATRACHOCHYTRIUM DENDROBATIDIS: A SYSTEMATIC REVIEW

Chytridiomycosis, caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), is a leading cause of global amphibian declines. Severe infections with Bd can lead to cardiac arrest, and mass deaths during epidemics have been reported. Temperature, pH, salinity, and moisture are important determinants of the survival, growth, reproduction, and pathogenicity of Bd, as well as its effect on amphibian populations. Here, we synthesize current knowledge on the role of temperature as a driver of the pathogenicity and virulence of Bd to better understand the effects of temperature on amphibian defense mechanisms against infection. This review advises on research direction and management approaches to benefit amphibian populations affected by Bd. We conclude by offering guidelines for four levels of temperature monitoring in amphibian field studies to improve consistency between studies: regional climate, habitat, microhabitat, and amphibian host.

Chytridiomycosis in Asian Amphibians, a Global Resource for Batrachochytrium dendrobatidis (Bd) Research

Chytridiomycosis is an emerging infectious disease affecting amphibians globally and it is caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd). Chytridiomycosis has caused dramatic declines and even extinctions in wild amphibian populations in Europe, Australia, Central and North America. Spanning over two and a half decades, extensive research has led to discovery of epizootic and enzootic lineages of this pathogen. However, the Bd–amphibian system had garnered less attention in Asia until recently when an ancestral Bd lineage was identified in the Korean peninsula. Amphibians co-exist with the pathogen in Asia, only sub-lethal effects have been documented on hosts. Such regions are ‘coldspots’ of infection and are an important resource to understand the dynamics between the enzootic pathogen—Bd and its obligate host—amphibians. Insights into the biology of infection have provided new knowledge on the multi-faceted interaction of Bd in a hyperdiverse Asian amphibian community. We present the findings and highlight the knowledge gap that exists, and propose the ways to bridge them. We emphasize that chytridiomycosis in Asia is an important wildlife disease and it needs focussed research, as it is a dynamic front of pathogen diversity and virulence.

Amphibian chytrid infections along the highest elevational gradient of the Brazilian Atlantic Forest

Environmental variation along elevational gradients shapes conditions for pathogen development, which influences disease outcomes. Chytridiomycosis is a non-vectored disease caused by the aquatic fungus Batrachochytrium dendrobatidis (Bd) and is responsible for massive declines of amphibian populations all over the world. Several biotic and abiotic factors are known to influence Bd infection dynamics in amphibians, including temperature and host species richness. Here, we quantified Bd prevalence and load along an elevational gradient in the Caparaó National Park (CNP), Brazil, and tested for associations of Bd infections with elevation, temperature, and species richness. We hypothesized that Bd infections would increase as local species richness decreased with elevation. We detected Bd along the entire elevational gradient and found a negative association between infection load and elevation. We did not detect significant associations between infection prevalence and elevation. Our findings are consistent with other wide elevational gradient studies, but are contrary to 2 other studies performed in the Atlantic Forest. We did not find the minimum elevational range that should be sampled to detect the influence of elevation on Bd variation. Our study represents the widest elevational gradient that has been sampled in Brazil and contributes to a better understanding of Bd distribution and dynamics in natural systems.

Bad neighbours: amphibian chytrid fungus Batrachochytrium dendrobatidis infection dynamics in three co-occurring frog species of southern Sydney, Australia

Wildlife disease is a major cause of global biodiversity loss. Amongst the most devastating is the disease chytridiomycosis, caused by the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd). This disease has contributed to declines and extinctions in hundreds of amphibian species, but not all species are affected equally. Some amphibian hosts are capable of carrying high levels of Bd infection without population declines, acting as reservoir species for the pathogen and driving population declines in sympatric species. In Australia, several species have been proposed as reservoir species; however, our understanding of Bd is derived from studies that are highly geographically and taxonomically biased, and our ability to extrapolate from these systems is unknown. We examined the prevalence and intensity of Bd infection in 3 frog species in a previously unstudied host-pathogen system in temperate eastern Australia: the Blue Mountains tree frog Litoria citropa, a poorly-known species predicted to be susceptible to Bd infection; and the common eastern froglet Crinia signifera and the stony creek frog L. lesueuri, which have both been identified as reservoir species in other regions. We found that L. citropa and L. lesueuri were infected with Bd at a high prevalence and often high intensity, while the reverse was true for C. signifera. All species were detected at moderate abundance and there was no evidence of morbidity and mortality. Our findings do not support C. signifera and L. lesueuri being reservoir species in this system, highlighting the importance of region-specific studies to inform conservation management.

Cooler temperatures slow the repair of DNA damage in tadpoles exposed to ultraviolet radiation: Implications for amphibian declines at high altitude

Ultraviolet B radiation (UVBR) damages the DNA of exposed cells, causing dimers to form between adjacent pyrimidine nucleotides. These dimers block DNA replication, causing mutations and apoptosis. Most organisms utilize biochemical or biophysical DNA repair strategies to restore DNA structure; however, as with most biological reactions, these processes are likely to be thermally sensitive. Tadpoles exposed to elevated UVBR at low environmental temperatures have significantly higher rates of mortality and developmental deformities compared with tadpoles exposed to the same levels of UVBR at higher environmental temperatures. We hypothesized that low environmental temperatures impair the primary enzymatic (photolyase) DNA repair pathway in amphibians, leading to the accumulation of DNA damage. To test this hypothesis, we compared DNA repair rates and photolyase gene expression patterns in Limnodynastes peronii. Tadpoles were acutely exposed to UVBR for 1 hr at either 20 or 30°C, and we measured DNA damage and photolyase expression levels at intervals following this exposure. Temperature had a significant effect on the rate of DNA repair, with repair at 30°C occurring twice as fast as repair at 20°C. Photolyase gene expression (6-4 PP and CPD) was significantly upregulated by UVBR exposure, with expression levels increasing within 6 hr of UVBR exposure. CPD expression levels were not significantly affected by temperature, but 6-4 PP expression was significantly higher in tadpoles in the 30°C treatment within 12 hr of UVBR exposure. These data support the hypothesis that DNA repair rates are thermally sensitive in tadpoles and may explain why enigmatic amphibian declines are higher in montane regions where UVBR levels are naturally elevated and environmental temperatures are lower.

Chytrid fungi and global amphibian declines

Discovering that chytrid fungi cause chytridiomycosis in amphibians represented a paradigm shift in our understanding of how emerging infectious diseases contribute to global patterns of biodiversity loss. In this Review we describe how the use of multidisciplinary biological approaches has been essential to pinpointing the origins of amphibian-parasitizing chytrid fungi, including Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans, as well as to timing their emergence, tracking their cycles of expansion and identifying the core mechanisms that underpin their pathogenicity. We discuss the development of the experimental methods and bioinformatics toolkits that have provided a fuller understanding of batrachochytrid biology and informed policy and control measures.

Infection with Batrachochytrium dendrobatidis is common in tropical lowland habitats: Implications for amphibian conservation

Numerous species of amphibians declined in Central America during the 1980s and 1990s. These declines mostly affected highland stream amphibians and have been primarily linked to chytridiomycosis, a deadly disease caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd). Since then, the majority of field studies on Bd in the Tropics have been conducted in midland and highland environments (>800 m) mainly because the environmental conditions of mountain ranges match the range of ideal abiotic conditions for Bd in the laboratory. This unbalanced sampling has led researchers to largely overlook host-pathogen dynamics in lowlands, where other amphibian species declined during the same period. We conducted a survey testing for Bd in 47 species (n = 348) in four lowland sites in Costa Rica to identify local host-pathogen dynamics and to describe the abiotic environment of these sites. We detected Bd in three sampling sites and 70% of the surveyed species. We found evidence that lowland study sites exhibit enzootic dynamics with low infection intensity and moderate to high prevalence (55% overall prevalence). Additionally, we found evidence that every study site represents an independent climatic zone, where local climatic differences may explain variations in Bd disease dynamics. We recommend more detection surveys across lowlands and other sites that have been historically considered unsuitable for Bd occurrence. These data can be used to identify sites for potential disease outbreaks and amphibian rediscoveries.

Fungal infection has sublethal effects in a lowland subtropical amphibian population

BACKGROUND

The amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), has been implicated as a primary cause of decline in many species around the globe. However, there are some species and populations that are known to become infected in the wild, yet declines have not been observed. Here we conducted a yearlong capture-mark-recapture study and a 2-year long disease monitoring study of northern cricket frogs, Acris crepitans, in the lowland subtropical forests of Louisiana.

RESULTS

We found little evidence for an impact of Bd infection on survival; however, Bd infection did appear to cause sublethal effects, including increased capture probability in the field.

CONCLUSIONS

Our study suggests that even in apparently stable populations, where Bd does not appear to cause mortality, there may be sublethal effects of infection that can impact a host population's dynamics and structure. Understanding and documenting such sublethal effects of infection on wild, seemingly stable populations is important, particularly for predicting future population declines.

Exploring the link between ultraviolet B radiation and immune function in amphibians: implications for emerging infectious diseases

Amphibian populations the world over are under threat of extinction, with as many as 40% of assessed species listed as threatened under IUCN Red List criteria (a significantly higher proportion than other vertebrate group). Amongst the key threats to amphibian species is the emergence of novel infectious diseases, which have been implicated in the catastrophic amphibian population declines and extinctions seen in many parts of the world. The recent emergence of these diseases coincides with increased ambient levels of ultraviolet B radiation (UVBR) due to anthropogenic thinning of the Earth's protective ozone layer, raising questions about potential interactions between UVBR exposure and disease in amphibians. While reasonably well documented in other vertebrate groups (particularly mammals), the immunosuppressive capacity of UVBR and the potential for it to influence disease outcomes has been largely overlooked in amphibians. Herein, we review the evidence for UVBR-associated immune system disruption in amphibians and identify a number of direct and indirect pathways through which UVBR may influence immune function and disease susceptibility in amphibians. By exploring the physiological mechanisms through which UVBR may affect host immune function, we demonstrate how ambient UVBR could increase amphibian susceptibility to disease. We conclude by discussing the potential implications of elevated UVBR for inter and intraspecific differences in disease dynamics and discuss how future research in this field may be directed to improve our understanding of the role that UVBR plays in amphibian immune function.

Temporal Variation of the Skin Bacterial Community and Batrachochytrium dendrobatidis Infection in the Terrestrial Cryptic Frog Philoria loveridgei

In animals and plants, symbiotic bacteria can play an important role in disease resistance of host and are the focus of much current research. Globally, amphibian population declines and extinctions have occurred due to chytridiomycosis, a skin disease caused by the pathogen Batrachochytrium dendrobatidis (Bd). Currently amphibian skin bacteria are increasingly recognized as important symbiont communities with a relevant role in the defense against pathogens, as some bacteria can inhibit the growth of B. dendrobatidis. This study aims to document the B. dendrobatidis infection status of wild populations of a terrestrial cryptic frog (Philoria loveridgei), and to determine whether infection status is correlated with changes in the skin microbial communities. Skin samples of P. loveridgei were collected along an altitudinal range within the species distribution in subtropical rainforests in southeast Australia. Sampling was conducted in two years during two breeding seasons with the first classified as a “La Niña” year. We used Taqman real-time PCR to determine B. dendrobatidis infection status and 16S amplicon sequencing techniques to describe the skin community structure. We found B. dendrobatidis-positive frogs only in the second sampling year with low infection intensities, and no correlation between B. dendrobatidis infection status and altitude, frog sex or size. Skin bacterial diversity was significantly higher in P. loveridgei frogs sampled in the 1st year than in the 2nd year. In addition, 7.4% of the total OTUs were significantly more abundant in the 1st year compared to the 2nd year. We identified 67 bacterial OTUs with a significant positive correlation between infection intensity and an OTU’s relative abundance. Forty-five percent of these OTUs belonged to the family Enterobacteriaceae. Overall, temporal variation was strongly associated with changes in B. dendrobatidis infection status and bacterial community structure of wild populations of P. loveridgei.

High-Altitude-Induced alterations in Gut-Immune Axis: A review

High-altitude sojourn above 8000 ft is increasing day by day either for pilgrimage, mountaineering, holidaying or for strategic reasons. In India, soldiers are deployed to these high mountains for their duty or pilgrims visit to the holy places, which are located at very high altitude. A large population also resides permanently in high altitude regions. Every year thousands of pilgrims visit Holy cave of Shri Amarnath ji, which is above 15 000 ft. The poor acclimatization to high altitude may cause alteration in immunity. The low oxygen partial pressure may cause alterations in gut microbiota, which may cause changes in gut immunity. Effect of high altitude on gut-associated mucosal system is new area of research. Many studies have been carried out to understand the physiology and immunology behind the high-altitude-induced gut problems. Few interventions have also been discovered to circumvent the problems caused due to high-altitude conditions. In this review, we have discussed the effects of high-altitude-induced changes in gut immunity particularly peyer's patches, NK cells and inflammatory cytokines, secretary immunoglobulins and gut microbiota. The published articles from PubMed and Google scholar from year 1975 to 2017 on high-altitude hypoxia and gut immunity are cited in this review.

Rapid extirpation of a North American frog coincides with an increase in fungal pathogen prevalence: Historical analysis and implications for reintroduction

As extinctions continue across the globe, conservation biologists are turning to species reintroduction programs as one optimistic tool for addressing the biodiversity crisis. For repatriation to become a viable strategy, fundamental prerequisites include determining the causes of declines and assessing whether the causes persist in the environment. Invasive species-especially pathogens-are an increasingly significant factor contributing to biodiversity loss. We hypothesized that Batrachochytrium dendrobatidis (Bd), the causative agent of the deadly amphibian disease chytridiomycosis, was important in the rapid (<10 years) localized extirpation of a North American frog (Rana boylii) and that Bd remains widespread among extant amphibians in the region of extirpation. We used an interdisciplinary approach, combining interviews with herpetological experts, analysis of archived field notes and museum specimen collections, and field sampling of the extant amphibian assemblage to examine (1) historical relative abundance of R. boylii; (2) potential causes of R. boylii declines; and (3) historical and contemporary prevalence of Bd. We found that R. boylii were relatively abundant prior to their rapid extirpation, and an increase in Bd prevalence coincided with R. boylii declines during a time of rapid change in the region, wherein backcountry recreation, urban development, and the amphibian pet trade were all on the rise. In addition, extreme flooding during the winter of 1969 coincided with localized extirpations in R. boylii populations observed by interview respondents. We conclude that Bd likely played an important role in the rapid extirpation of R. boylii from southern California and that multiple natural and anthropogenic factors may have worked in concert to make this possible in a relatively short period of time. This study emphasizes the importance of recognizing historical ecological contexts in making future management and reintroduction decisions.

Differential patterns of Batrachochytrium dendrobatidis infection in relict amphibian populations following severe disease-associated declines

Global amphibian biodiversity has declined dramatically in the past 4 decades, and many amphibian species have declined to near extinction as a result of emergence of the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd). However, persistent or recovering populations of several amphibian species have recently been rediscovered, and such populations may illustrate how amphibian species that are highly susceptible to chytridiomycosis may survive in the presence of Bd. We conducted field surveys for Bd infection in 7 species of Costa Rican amphibians (all species that have declined to near extinction but for which isolated populations persist) to characterize infection profiles in highly Bd-susceptible amphibians post-decline. We found highly variable patterns in infection, with some species showing low prevalence (~10%) and low infection intensity and others showing high infection prevalence (>80%) and either low or high infection intensity. Across sites, infection rates were negatively associated with mean annual precipitation, and infection intensity across sites was negatively associated with mean average temperatures. Our results illustrate that even the most Bd-susceptible amphibians can persist in Bd-enzootic ecosystems, and that multiple ecological or evolutionary mechanisms likely exist for host-pathogen co-existence between Bd and the most Bd-susceptible amphibian species. Continued monitoring of these populations is necessary to evaluate population trends (continuing decline, stability, or population growth). These results should inform efforts to mitigate impacts of Bd on amphibians in the field.

Inhibition of Fungal Pathogens across Genotypes and Temperatures by Amphibian Skin Bacteria

Symbiotic bacteria may dampen the impacts of infectious diseases on hosts by inhibiting pathogen growth. However, our understanding of the generality of pathogen inhibition by different bacterial taxa across pathogen genotypes and environmental conditions is limited. Bacterial inhibitory properties are of particular interest for the amphibian-killing fungal pathogens (Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans), for which probiotic applications as conservation strategies have been proposed. We quantified the inhibition strength of five putatively B. dendrobatidis-inhibitory bacteria isolated from woodland salamander skin against six Batrachochytrium genotypes at two temperatures (12 and 18°C). We selected six genotypes from across the Batrachochytrium phylogeny: B. salamandrivorans, B. dendrobatidis-Brazil and four genotypes of the B. dendrobatidis Global Panzootic Lineage (GPL1: JEL647, JEL404; GPL2: SRS810, JEL423). We performed 96-well plate challenge assays in a full factorial design. We detected a Batrachochytrium genotype by temperature interaction on bacterial inhibition score for all bacteria, indicating that bacteria vary in ability to inhibit Batrachochytrium depending on pathogen genotype and temperature. Acinetobacter rhizosphaerae moderately inhibited B. salamandrivorans at both temperatures (μ = 46–53%), but not any B. dendrobatidis genotypes. Chryseobacterium sp. inhibited three Batrachochytrium genotypes at both temperatures (μ = 5–71%). Pseudomonas sp. strain 1 inhibited all Batrachochytrium genotypes at 12°C and four Batrachochytrium genotypes at 18°C (μ = 5–100%). Pseudomonas sp. strain 2 and Stenotrophomonas sp. moderately to strongly inhibited all six Batrachochytrium genotypes at both temperatures (μ = 57–100%). All bacteria consistently inhibited B. salamandrivorans. Using cluster analysis of inhibition scores, we found that more closely related Batrachochytrium genotypes grouped together, suggesting that bacterial inhibition strength may be predictable based on Batrachochytrium relatedness. We conclude that bacterial inhibition capabilities change among bacterial strains, Batrachochytrium genotypes and temperatures. A comprehensive understanding of bacterial inhibitory function, across pathogen genotypes and temperatures, is needed to better predict the role of bacterial symbionts in amphibian disease ecology. For targeted conservation applications, we recommend using bacterial strains identified as strongly inhibitory as they are most likely to produce broad-spectrum antimicrobial agents at a range of temperatures.

Variation in Metabolite Profiles of Amphibian Skin Bacterial Communities Across Elevations in the Neotropics

Both the structure and function of host-associated microbial communities are potentially impacted by environmental conditions, just as the outcomes of many free-living species interactions are context-dependent. Many amphibian populations have declined around the globe due to the fungal skin pathogen, Batrachochytrium dendrobatidis (Bd), but enivronmental conditions may influence disease dynamics. For instance, in Panamá, the most severe Bd outbreaks have occurred at high elevation sites. Some amphibian species harbor bacterial skin communities that can inhibit the growth of Bd, and therefore, there is interest in understanding whether environmental context could also alter these host-associated microbial communities in a way that might ultimately impact Bd dynamics. In a field survey in Panamá, we assessed skin bacterial communities (16S rRNA amplicon sequencing) and metabolite profiles (HPLC-UV/Vis) of Silverstoneia flotator from three high- and three low-elevation populations representing a range of environmental conditions. Across elevations, frogs had similar skin bacterial communities, although one lowland site appeared to differ. Interestingly, we found that bacterial richness decreased from west to east, coinciding with the direction of Bd spread through Panamá. Moreover, metabolite profiles suggested potential functional variation among frog populations and between elevations. While the frogs have similar bacterial community structure, the local environment might shape the metabolite profiles. Ultimately, host-associated community structure and function could be dependent on environmental conditions, which could ultimately influence host disease susceptibility across sites.

Diversity in growth patterns among strains of the lethal fungal pathogen Batrachochytrium dendrobatidis across extended thermal optima

The thermal sensitivities of organisms regulate a wide range of ecological interactions, including host–parasite dynamics. The effect of temperature on disease ecology can be remarkably complex in disease systems where the hosts are ectothermic and where thermal conditions constrain pathogen reproductive rates. Amphibian chytridiomycosis, caused by the pathogen Batrachochytrium dendrobatidis (Bd), is a lethal fungal disease that is influenced by temperature. However, recent temperature studies have produced contradictory findings, suggesting that our current understanding of thermal effects on Bd may be incomplete. We investigated how temperature affects three different Bd strains to evaluate diversity in thermal responses. We quantified growth across the entire thermal range of Bd, and beyond the known thermal limits (T_max and T_min). Our results show that all Bd strains remained viable and grew following 24 h freeze (−12 °C) and heat shock (28 °C) treatments. Additionally, we found that two Bd strains had higher logistic growth rates (r) and carrying capacities (K) at the upper and lower extremities of the temperature range, and especially in low temperature conditions (2–3 °C). In contrast, a third strain exhibited relatively lower growth rates and carrying capacities at these same thermal extremes. Overall, our results suggest that there is considerable variation among Bd strains in thermal tolerance, and they establish a new thermal sensitivity profile for Bd. More generally, our findings point toward important questions concerning the mechanisms that dictate fungal thermal tolerances and temperature-dependent pathogenesis in other fungal disease systems.

Seasonal Variation in Population Abundance and Chytrid Infection in Stream-Dwelling Frogs of the Brazilian Atlantic Forest

Enigmatic amphibian declines were first reported in southern and southeastern Brazil in the late 1980s and included several species of stream-dwelling anurans (families Hylodidae and Cycloramphidae). At that time, we were unaware of the amphibian-killing fungus Batrachochytrium dendrobatidis (Bd); therefore, pollution, habitat loss, fragmentation and unusual climatic events were hypothesized as primary causes of these declines. We now know that multiple lineages of Bd have infected amphibians of the Brazilian Atlantic forest for over a century, yet declines have not been associated specifically with Bd outbreaks. Because stream-dwelling anurans occupy an environmental hotspot ideal for disease transmission, we investigated temporal variation in population and infection dynamics of three stream-adapted species (Hylodes asper, H. phyllodes, and Cycloramphus boraceiensis) on the northern coast of São Paulo state, Brazil. We surveyed standardized transects along streams for four years, and show that fluctuations in the number of frogs correlate with specific climatic variables that also increase the likelihood of Bd infections. In addition, we found that Bd infection probability in C. boraceiensis, a nocturnal species, was significantly higher than in Hylodes spp., which are diurnal, suggesting that the nocturnal activity may either facilitate Bd zoospore transmission or increase susceptibility of hosts. Our findings indicate that, despite long-term persistence of Bd in Brazil, some hosts persist with seasonally variable infections, and thus future persistence in the face of climate change will depend on the relative effect of those changes on frog recruitment and pathogen proliferation.

Widespread occurrence of bd in French Guiana, South America

The amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) is a purported agent of decline and extinction of many amphibian populations worldwide. Its occurrence remains poorly documented in many tropical regions, including the Guiana Shield, despite the area's high amphibian diversity. We conducted a comprehensive assessment of Bd in French Guiana in order to (1) determine its geographical distribution, (2) test variation of Bd prevalence among species in French Guiana and compare it to earlier reported values in other South American anuran species (http://www.bd-maps.net; 123 species from 15 genera) to define sentinel species for future work, (3) track changes in prevalence through time and (4) determine if Bd presence had a negative effect on one selected species. We tested the presence of Bd in 14 species at 11 sites for a total of 1053 samples (306 in 2009 and 747 in 2012). At least one Bd-positive individual was found at eight out of 11 sites, suggesting a wide distribution of Bd in French Guiana. The pathogen was not uniformly distributed among the studied amphibian hosts, with Dendrobatidae species displaying the highest prevalence (12.4%) as compared to Bufonidae (2.6 %) and Hylidae (1.5%). In contrast to earlier reported values, we found highest prevalence for three Dendrobatidae species and two of them displayed an increase in Bd prevalence from 2009 to 2012. Those three species might be the sentinel species of choice for French Guiana. For Dendrobates tinctorius, of key conservation value in the Guiana Shield, smaller female individuals were more likely to be infected, suggesting either that frogs can outgrow their chytrid infections or that the disease induces developmental stress limiting growth. Generally, our study supports the idea that Bd is more widespread than previously thought and occurs at remote places in the lowland forest of the Guiana shield.

Elevated Corticosterone Levels and Changes in Amphibian Behavior Are Associated with Batrachochytrium dendrobatidis (Bd) Infection and Bd Lineage

Few studies have examined the role hormones play in mediating clinical changes associated with infection by the parasite Batrachochytrium dendrobatidis (Bd). Glucocorticoid (GC) hormones such as corticosteroids (CORT) regulate homeostasis and likely play a key role in response to infection in amphibians. We explore the relationship between CORT release rates and Bd infection in tadpoles of the common midwife toad, Alytes obstetricians, using a non-invasive water-borne hormone collection method across seven populations. We further examined whether tadpoles of A. muletensis infected with a hypervirulent lineage of Bd, BdGPL, had greater CORT release rates than those infected with a hypovirulent lineage, BdCAPE. Finally, we examined the relationship between righting reflex and CORT release rates in infected metamorphic toads of A. obstetricans. We found an interaction between elevation and Bd infection status confirming that altitude is associated with the overall severity of infection. In tandem, increasing elevation was associated with increasing CORT release rates. Tadpoles infected with the hypervirulent BdGPL had significantly higher CORT release rates than tadpoles infected with BdCAPE showing that more aggressive infections lead to increased CORT release rates. Infected metamorphs with higher CORT levels had an impaired righting reflex, our defined experimental endpoint. These results provide evidence that CORT is associated with an amphibian’s vulnerability to Bd infection, and that CORT is also affected by the aggressiveness of infection by Bd. Together these results indicate that CORT is a viable biomarker of amphibian stress.

Population stability in the endangered Fleay’s barred frog (Mixophyes fleayi) and a program for long-term monitoring

In the wake of the global decline in amphibians there is a need for long-term population monitoring. Previous research suggested that the endangered Fleay’s barred frog (Mixophyes fleayi) had recovered after a severe decline. We aimed to determine whether this recovery has been sustained and to test an example of a monitoring program that could be employed at intervals of five or more years to assess long-term population stability. We conducted capture–mark–recapture five years after the last detailed census at Brindle Creek in Border Ranges National Park, New South Wales. Frogs were captured along a 200 m creek transect between September 2013 and February 2014. We used program Mark to estimate demographic parameters of adult male frogs using two modelling approaches: robust design (RD) and the POPAN formulation of the Jolly–Seber model. Abundance was estimated at 38.2 ± 0.5 (s.e.) (RD) and 46.0 ± 2.7 (POPAN). Abundance in 2008 was estimated at 53.2 ± 10.0 (POPAN) male frogs. Estimates of apparent monthly survival over our five-month-long study were very high (RD: 1.0 ± 0.0; POPAN: 1.0 ± 0.02). Recapture estimates were also high (RD: 0.40 ± 0.07 to 0.72 ± 0.05 per session; POPAN: 0.84 ± 0.05 per month). These data suggest that the Brindle Creek population has remained relatively stable over a period of ~10 years.

Cool temperatures reduce antifungal activity of symbiotic bacteria of threatened amphibians--implications for disease management and patterns of decline

Chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), is a widespread disease of amphibians responsible for population declines and extinctions. Some bacteria from amphibians' skins produce antimicrobial substances active against Bd. Supplementing populations of these cutaneous antifungal bacteria might help manage chytridiomycosis in wild amphibians. However, the activity of protective bacteria may depend upon environmental conditions. Biocontrol of Bd in nature thus requires knowledge of how environmental conditions affect their anti-Bd activity. For example, Bd-driven amphibian declines have often occurred at temperatures below Bd's optimum range. It is possible these declines occurred due to reduced anti-Bd activity of bacterial symbionts at cool temperatures. Better understanding of the effects of temperature on chytridiomycosis development could also improve risk evaluation for amphibian populations yet to encounter Bd. We characterized, at a range of temperatures approximating natural seasonal variation, the anti-Bd activity of bacterial symbionts from the skins of three species of rainforest tree frogs (Litoria nannotis, Litoria rheocola, and Litoria serrata). All three species declined during chytridiomycosis outbreaks in the late 1980s and early 1990s and have subsequently recovered to differing extents. We collected anti-Bd bacterial symbionts from frogs and cultured the bacteria at constant temperatures from 8 °C to 33 °C. Using a spectrophotometric assay, we monitored Bd growth in cell-free supernatants (CFSs) from each temperature treatment. CFSs from 11 of 24 bacteria showed reduced anti-Bd activity in vitro when they were produced at cool temperatures similar to those encountered by the host species during population declines. Reduced anti-Bd activity of metabolites produced at low temperatures may, therefore, partially explain the association between Bd-driven declines and cool temperatures. We show that to avoid inconsistent antifungal activity, bacteria evaluated for use in chytridiomycosis biocontrol should be tested over a range of environmental temperatures spanning those likely to be encountered in the field.

Elevation, temperature, and aquatic connectivity all influence the infection dynamics of the amphibian chytrid fungus in adult frogs

Infectious diseases can cause population declines and even extinctions. The amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), has caused population declines and extinctions in amphibians on most continents. In the tropics, research on the dynamics of this disease has focused on amphibian populations in mountainous areas. In most of these areas, high and low elevation sites are connected by an assemblage of streams that may transport the infectious stage of the pathogen from high to low elevations, and, also, this pathogen, which grows well at cool temperatures, may persist better in cooler water flowing from high elevations. Thus, the dynamics of disease at low elevation sites without aquatic connections to higher elevation sites, i.e., non-contiguous low elevation sites, may differ from dynamics at contiguous low elevation sites. We sampled adult common mistfrogs (Litoria rheocola) at six sites of three types: two at high (> 400m) elevations, two at low elevations contiguous with high elevation streams, and two at low elevations non-contiguous with any high elevation site. Adults were swabbed for Bd diagnosis from June 2010 to June 2011 in each season, over a total of five sampling periods. The prevalence of Bd fluctuated seasonally and was highest in winter across all site types. Site type significantly affected seasonal patterns of prevalence of Bd. Prevalence remained well above zero throughout the year at the high elevation sites. Prevalence declined to lower levels in contiguous low sites, and reached near-zero at non-contiguous low sites. Patterns of air temperature fluctuation were very similar at both the low elevation site types, suggesting that differences in water connectivity to high sites may have affected the seasonal dynamics of Bd prevalence between contiguous and non-contiguous low elevation site types. Our results also suggest that reservoir hosts may be important in the persistence of disease at low elevations.

Non-invasive monitoring of glucocorticoid physiology within highland and lowland populations of native Australian Great Barred Frog (Mixophyes fasciolatus)

This study used non-invasive endocrinology to examine baseline corticosterone at different altitudes in a free-living Australian amphibian: the Great Barred Frog (Mixophyes fasciolatus). An enzyme immunoassay (EIA) was performed on urine samples and validated biologically using an adrenocorticotropic hormone (ACTH) challenge. Frogs were injected with ACTH on day 0 and recaptures occurred 1-10days post injection. Urine samples and body condition measurements were collected from lowland (60m) and highland (660m and 790m) sub-populations of M. fasciolatus in South East Queensland (SEQ), close to their post-breeding period during autumn 2011. We simultaneously sampled these sub-populations for Batrachochytrium dendrobatidis (Bd), a pathogenic fungus responsible for mass mortalities of amphibians worldwide. The ACTH challenge successfully validated the urinary corticosterone EIA in M. fasciolatus, with a peak urinary corticosterone response to ACTH injection on day 2 and a return to baseline levels by day 6. Polymerase chain reaction (PCR) analysis of 50 individuals returned only 1 positive result for Bd. Simple linear regression showed a strong positive relationship between baseline urinary corticosterone concentrations and altitude and no relationship with body condition. We hypothesize that higher baseline corticosterone concentrations within highland sub-populations of male M. fasciolatus could be associated with increased environmental challenge at high altitudes and geographic range limits. Whether this pattern is an indication of chronic stress in highland populations or life-time fitness and survival, warrants future investigation.

Population recovery following decline in an endangered stream-breeding frog (Mixophyes fleayi) from subtropical Australia

Amphibians have undergone dramatic declines and extinctions worldwide. Prominent among these have been the stream-breeding frogs in the rainforests of eastern Australia. The amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) has been postulated as the primary cause of these declines. We conducted a capture-mark-recapture study over a 7-year period on the endangered Fleay’s barred frog (Mixophyes fleayi) at two independent streams (30 km apart) in order to assess the stability of these populations. This species had undergone a severe decline across its narrow geographic range. Mark-recapture modelling showed that the number of individuals increased 3–10 fold along stream transects over this period. Frog detection probabilities were frequently above 50% but declined as the populations increased. Adult survival was important to overall population persistence in light of low recruitment events, suggesting that longevity may be a key factor in this recovery. One male and female were present in the capture record for >6 years. This study provides an unambiguous example of population recovery in the presence of Bd.

Non-invasive reproductive and stress endocrinology in amphibian conservation physiology

Non-invasive endocrinology utilizes non-invasive biological samples (such as faeces, urine, hair, aquatic media, and saliva) for the quantification of hormones in wildlife. Urinary-based enzyme immunoassay (EIA) and radio-immunoassay have enabled the rapid quantification of reproductive and stress hormones in amphibians (Anura: Amphibia). With minimal disturbance, these methods can be used to assess the ovarian and testicular endocrine functions as well as physiological stress in captive and free-living populations. Non-invasive endocrine monitoring has therefore greatly advanced our knowledge of the functioning of the stress endocrine system (the hypothalamo-pituitary-interrenal axis) and the reproductive endocrine system (the hypothalamo-pituitary-gonadal axis) in the amphibian physiological stress response, reproductive ecology, health and welfare, and survival. Biological (physiological) validation is necessary for obtaining the excretory lag time of hormone metabolites. Urinary-based EIA for the major reproductive hormones, estradiol and progesterone in females and testosterone in males, can be used to track the reproductive hormone profiles in relationship to reproductive behaviour and environmental data in free-living anurans. Urinary-based corticosterone metabolite EIA can be used to assess the sublethal impacts of biological stressors (such as invasive species and pathogenic diseases) as well as anthropogenic induced environmental stressors (e.g. extreme temperatures) on free-living populations. Non-invasive endocrine methods can also assist in the diagnosis of success or failure of captive breeding programmes by measuring the longitudinal patterns of changes in reproductive hormones and corticosterone within captive anurans and comparing the endocrine profiles with health records and reproductive behaviour. This review paper focuses on the reproductive and the stress endocrinology of anurans and demonstrates the uses of non-invasive endocrinology for advancing amphibian conservation physiology. It also provides key technical considerations for future research that will increase the accuracy and reliability of the data and the value of non-invasive endocrinology within the conceptual framework of conservation physiology.

Changes in cutaneous microbial abundance with sloughing: possible implications for infection and disease in amphibians

The emergence of disease as a significant global threat to amphibian diversity has generated considerable interest in amphibian defenses against cutaneous microbial infection and disease. To date, however, the influence of sloughing on the susceptibility of amphibians to infection and disease has been largely overlooked. To investigate the potential for sloughing to regulate topical microbial loads, the abundance of cultivable cutaneous bacteria and fungi in the cane toad Rhinella marina were compared before and after sloughing. Toads were also exposed to fluctuating thermal regimes (10-20 and 20-30°C) and variable photoperiods to investigate possible effects of season and climate on sloughing periodicity. Sloughing substantially reduced the abundance of cultivable cutaneous bacteria and fungi by up to 100%. The intermoult interval of toads maintained at 10-20°C was twice that of animals at 20-30°C and did not appear to thermally acclimate. Photoperiod had no discernable influence on sloughing periodicity. Results of this study suggest that normal sloughing cycles could play a significant role in controlling the persistence and build-up of cutaneous microbes, including pathogens. The loss of non-pathogenic commensal and protective skin microbiota after sloughing may also influence host susceptibility to cutaneous pathogens. We suggest that the spatio-temporal dynamics of chytridiomycosis, the widespread and often fatal disease caused by the fungal pathogen Batrachochytrium dendrobatidis, are related to temperature not only because of its effect on the growth of the fungus, but also because of its effect on the frequency of host sloughing.

Potential influence of plant chemicals on infectivity of Batrachochytrium dendrobatidis

We explored whether extracts of trees frequently found associated with amphibian habitats in Australia and Arizona, USA, may be inhibitory to the fungal pathogen Batrachochytrium dendrobatidis (Bd), which has been associated with global amphibian declines. We used salamanders Ambystoma tigrinum as the model system. Salamanders acquired significantly lower loads of Bd when exposed on leaves and extracts from the river red gum Eucalyptus camaldulensis, and loads were also low in some animals exposed on extracts of 2 oak species, Quercus emoryi and Q. turbinella. Some previously infected salamanders had their pathogen loads reduced, and some were fully cured, by placing them in leaf extracts, although some animals also self cured when housed in water alone. A significant number of animals cured of Bd infections 6 mo earlier were found to be resistant to reinfection. These results suggest that plants associated with amphibian habitats should be taken into consideration when explaining the prevalence of Bd in these habitats and that some amphibians may acquire resistance to the fungus if previously cured.

Bd on the beach: high prevalence of Batrachochytrium dendrobatidis in the lowland forests of Gorgona Island (Colombia, South America)

The amphibian chytrid fungus, Batrachochytrium dendrobatidis, Bd, has been implicated in the decimation and extinction of many amphibian populations worldwide, especially at mid and high elevations. Recent studies have demonstrated the presence of the pathogen in the lowlands from Australia and Central America. We extend here its elevational range by demonstrating its presence at the sea level, in the lowland forests of Gorgona Island, off the Pacific coast of Colombia. We conducted two field surveys, separated by four years, and diagnosed Bd by performing polymerase chain reactions on swab samples from the skin of five amphibian species. All species, including the Critically Endangered Atelopus elegans, tested positive for the pathogen, with prevalences between 3.9 % in A. elegans (in 2010) and 52 % in Pristimantis achatinus. Clinical signs of chytridiomycosis were not detected in any species. To our knowledge, this is the first report of B. dendrobatidis in tropical lowlands at sea level, where temperatures may exceed optimal growth temperatures of this pathogen. This finding highlights the need to understand the mechanisms allowing the interaction between frogs and pathogen in lowland ecosystems.

Field and laboratory studies of the susceptibility of the green treefrog (Hyla cinerea) to Batrachochytrium dendrobatidis infection

Amphibians worldwide are experiencing devastating declines, some of which are due to the amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd). Populations in the southeastern United States, however, have not been noticeably affected by the pathogen. The green treefrog (Hyla cinerea) is abundant and widespread in the southeastern United States, but has not been documented to harbor Bd infection. This study examined the susceptibility of H. cinerea to two strains of Bd in the lab and the prevalence of infection in wild populations of this species in southeastern Louisiana. Although we were able to infect H. cinerea with Bd in the lab, we did not observe any clinical signs of chytridiomycosis. Furthermore, infection by Bd does not appear to negatively affect body condition or growth rate of post-metamorphic individuals. We found no evidence of infection in surveys of wild H. cinerea. Our results suggest that H. cinerea is not susceptible to chytridiomycosis post-metamorphosis and probably is not an important carrier of the fungal pathogen Bd in the southeastern United States, although susceptibility at the larval stage remains unknown.

Does simultaneous UV-B exposure enhance the lethal and sub-lethal effects of aquatic hypoxia on developing anuran embryos and larvae?

Recent catastrophic global amphibian declines have been partially linked to increases in UV-B radiation as a consequence of stratospheric ozone depletion. Previous studies have shown that in the presence of other environmental stressors including aquatic pH and temperature and the presence of contaminants or pathogens, the lethal effects of UV-B on amphibian larvae are enhanced due to interactions between the stressors. Little is known about the interactions between UV-B and aquatic hypoxia, a common and significant natural stressor of amphibian larvae. We examined the potential effects of UV-B and aquatic hypoxia in combination on embryonic survival, developmental rate, body mass and locomotor performance of embryos and larvae of the striped marsh frog, Limnodynastes peronii. We found that while both UV-B and hypoxia independently had substantial negative effects on the developing embryos of L. peronii, they did not interact in a multiplicative or antagonistic manner. The effects of the stressors in combination were as might be predicted based on the knowledge of their independent actions alone (i.e. an additive effect). In all cases developing embryos exposed to both UV-B and hypoxia were more severely affected than those exposed to either UV-B or hypoxia alone. The results of this study show the importance of examining both the direct actions of individual stressors and how these may be influenced by the presence of other environmental factors.

What drives chytrid infections in newt populations? Associations with substrate, temperature, and shade

The pathogenic chytrid fungus Batrachochytrium dendrobatidis (Bd) is considered responsible for the population declines and extinctions of hundreds of amphibian species worldwide. The panzootic was likely triggered by human-assisted spread, but once the pathogen becomes established in a given region, its distribution is probably determined by local drivers. To assess the relative importance of potential drivers of infection in red-spotted newts (Notophthalmus viridescens), we measured Bd levels in 16 populations throughout central Pennsylvania. Infected individuals were detected in all but four populations, indicating that Bd is widespread in this region. We quantified local factors hypothesized to influence Bd, and found that infection levels were best predicted by the proportion of the pond substrate consisting of leaf litter or vegetation, along with a significant effect of water temperature. Bd infection in amphibians is temperature-dependent, and one possible explanation of the apparent substrate effect is that tree cover and vegetation provide shade, reducing the availability of shallow, warm-water patches in which newts might reduce or clear Bd infections. Alternatively, leaf litter and emergent vegetation might increase Bd infection more directly, perhaps by providing substrates for environmental growth of the fungus. We also observed a curvilinear relationship between Bd load and snout-vent length (a proxy for age), hinting that newts might develop acquired resistance to Bd infection. Though correlational, these results add to a growing body of evidence suggesting that environmental temperature is an important driver of Bd infection dynamics.

Ubiquity of the pathogenic chytrid fungus, Batrachochytrium dendrobatidis, in Anuran communities in Panamá

The pathogenic chytrid fungus, Batrachochytrium dendrobatidis, has been implicated as the main driver of many enigmatic amphibian declines in neotropical sites at high elevation. Batrachochytrium dendrobatidis is thought to be a waterborne pathogen limited by temperature, and the extent to which it persists and causes disease in amphibians at lower elevations in the neotropics is not known. It also is unclear by what mechanism(s) B. dendrobatidis has emerged as a pathogenic organism. To test whether B. dendrobatidis is limited by elevation in Panamá, we sought to determine the prevalence and intensity of B. dendrobatidis in relation to anuran abundance and diversity using quantitative PCR (qPCR) analyses. Sites were situated at varying elevations, from 45 to 1215 m, and were at varying stages of epizootic amphibian decline, including pre-epizootic, mid-epizootic, 2 years post-epizootic, and 10 years post-epizootic. Batrachochytrium dendrobatidis was found in all sites regardless of elevation or stage of epizootic decline. Levels of prevalence and infection intensity were comparable across all sites except at the mid-epizootic site, where both prevalence and intensity were significantly higher than at other sites. Symptoms of chytridiomycosis and corresponding declines in amphibian populations were variably seen at all elevations along a post-epizootic gradient. Because it is inherently difficult to prove a negative proposition, it can neither be proven that B. dendrobatidis is truly not present where it is not detected nor proven that it is only recently arrived where it is detected. Thus, there will always be doubts about whether B. dendrobatidis is enzootic or invasive. In any case, our results, coupled with current knowledge, suggest most clearly that the disease, chytridiomycosis, may be novel and invasive, and that the pathogen, B. dendrobatidis either is, or is becoming, globally ubiquitous.

Epidemic disease decimates amphibian abundance, species diversity, and evolutionary history in the highlands of central Panama

Amphibian populations around the world are experiencing unprecedented declines attributed to a chytrid fungal pathogen, Batrachochytrium dendrobatidis. Despite the severity of the crisis, quantitative analyses of the effects of the epidemic on amphibian abundance and diversity have been unavailable as a result of the lack of equivalent data collected before and following disease outbreak. We present a community-level assessment combining long-term field surveys and DNA barcode data describing changes in abundance and evolutionary diversity within the amphibian community of El Copé, Panama, following a disease epidemic and mass-mortality event. The epidemic reduced taxonomic, lineage, and phylogenetic diversity similarly. We discovered that 30 species were lost, including five undescribed species, representing 41% of total amphibian lineage diversity in El Copé. These extirpations represented 33% of the evolutionary history of amphibians within the community, and variation in the degree of population loss and decline among species was random with respect to the community phylogeny. Our approach provides a fast, economical, and informative analysis of loss in a community whether measured by species or phylogenetic diversity.

Population age structure of the spotted tree frog (Litoria spenceri): insights into population declines

Context. Despite increased scientific attention on amphibian conservation in recent years, knowledge of population demography of amphibians remains scarce, hampering evaluation of population declines and development of appropriate management responses. Aims. The aims of this research were to examine variation in population demography of the spotted tree frog (Litoria spenceri), a critically endangered species in Australia, and to evaluate the role of various factors potentially responsible for population declines such as introduced trout, chytridiomycosis and habitat changes. Methods. Skeletochronology combined with mark–recapture sampling were undertaken in two different river systems, Bogong Creek and Taponga River, to determine population age structure. Age-specific survival estimates were derived from each population and were then used to examine variance in age-specific mortality. Key results. Relative population density per 200 m of stream was 67.7 adults and 131.3 juveniles at Bogong Creek and 10.7 adults and 33.8 juveniles at Taponga River. Ages were determined for 578 frogs across the two populations. Age-specific survival was lowest in the first year of life compared to all other age classes, and highest in sexually mature adults. Differences in age-specific survival were similar between the populations, with the exception of first-year survivorship, which averaged 1.9% at Bogong Creek and 0.4% at Taponga River. This difference was large enough to explain most of the marked difference in population density between the two streams. Key conclusions. The difference in first-year age-specific survival is consistent with trout predation as the most parsimonious explanation for the large differences in population density between the populations, and lends further weight to the role of introduced trout in the decline of this species. Implications. This study has contributed to informing management actions for conservation of this species, and demonstrates that population age structure data may provide valuable insights into demographic variability within and between populations and species. This may have important implications for interpretation of population declines, and conservation and management responses.