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Batrachochytrium dendrobatidis (Bd), an aquatic pathogenic fungus, is responsible for the decline of hundreds of amphibian species worldwide and negatively impacts biodiversity globally. Prophylactic exposure to the metabolites produced by Bd can provide protection for naïve tree frogs and reduce subsequent Bd infection intensity. Here, we used a response surface design crossing Bd metabolite prophylaxis concentration and exposure duration to determine how these factors modulate prophylactic protection against Bd in Pacific chorus frog (Pseudacris regilla) tadpoles (5 × 5 surface design) and metamorphs (3 × 3 surface design). We exposed individuals every weekday to one of five Bd metabolite concentrations or a water control for 1–5 weeks, after which all animals were challenged with live Bd to evaluate their susceptibility. Exposure to the Bd metabolite prophylaxis reduced Bd load and prevalence compared to the control for both the tadpoles and metamorphs. Increasing Bd metabolite prophylaxis concentration did not confer additional protection for either life stage, but increasing duration of exposure did benefit metamorphs by decreasing Bd prevalence but not Bd load. On average, control tadpoles and metamorphs had 66.2% and 99.4% higher Bd loads, respectively, than tadpoles and metamorphs exposed to any Bd metabolite prophylaxis. Additionally, Bd metabolite prophylaxis reduced Bd prevalence relative to controls in both tadpoles (20.5% vs. 56.3%, respectively) and metamorphs (21.9% vs. 87.5%, respectively). Synthesis and applications: The efficacy of short‐term exposures of relatively low concentrations of Bd metabolites at reducing Bd infections suggests that this approach has the potential to be scaled up to field use to aid in disease mitigation and conservation. Our results, combined with additional research on Bd metabolite prophylaxis for other amphibian species, suggest that this strategy may represent a broadly useful tool to protect at‐risk amphibian populations. [ABSTRACT FROM AUTHOR]

To characterize the potential for exposure of amphibian terrestrial life stages to plant protection products (PPP), we studied the occurrence and habitat use of adult and metamorph common frogs (Rana temporaria) and common toads (Bufo bufo) in an agricultural landscape in Germany. The four selected study sites were breeding ponds with approximately 80% agricultural land within a 1‐km radius. Adults were monitored by radio tracking for two years, and metamorph numbers were assessed for one summer using pitfall traps alongside drift fences. The results demonstrate that adults were rarely present in arable fields at any of the sites (overall 0.5% and 4% of total observations for frogs and toads, respectively). Metamorph captures in arable fields were more variable, ranging from 1.2% to 38.8% (frogs) and from 0.0% to 26.1% (toads) across study sites. Unsurprisingly, most captures in arable fields for both toad and frog metamorphs occurred at the site where the pond was completely surrounded by arable fields. Overall, the presence of adult amphibians in arable fields was limited and, for the metamorphs, occurred primarily when crops were denser and PPP spray interception higher. Diurnal hiding behavior was observed with the highest activity recorded at night, further reducing the risk of dermal exposure from direct PPP overspraying. In addition, it appeared that alternative habitats, such as woody structures or water bodies in the broader surrounding area, were preferred by the animals over the arable areas. The use of buffer zones around water bodies in agricultural areas would be an effective risk mitigation measure to protect terrestrial adults and metamorphs residing there and would reduce spray drift entry into water bodies during PPP application. It is hoped that these results will contribute to the discussion of risk assessment and mitigation options for amphibians. Integr Environ Assess Manag 2024;20:2218–2230. © 2024 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). Key Points: Relevant potential exposure for both adult and metamorph anuran amphibians (i.e., common frogs and toads) on agricultural land was assessed.The movement and behavior of both adult and metamorph common frogs and common toads exhibited a preference for nonarable habitats and reduced potential for exposure.Landscape management is an option to protect and support amphibian populations effectively. [ABSTRACT FROM AUTHOR]

Two key epidemiological parameters, prevalence and mean intensity of infection, together capture the abundance of macroparasite populations, the strength of density-dependent effects they experience, their potential impact on host population dynamics and the selective pressures they exert on their hosts. Yet, the drivers of the extensive variation observed in prevalence and mean intensity of infection, even among related parasite taxa infecting related hosts, remain mostly unknown. We performed phylogenetically grounded Bayesian modelling across hundreds of amphibian populations to test the effects of various predictors of prevalence and intensity of infection by six families of helminth parasites. We focused on the potential effects of key host traits and environmental factors pertinent to focal host populations, i.e. the local diversity of the amphibian community and local climatic variables. Our analyses revealed several important determinants of prevalence or intensity of infection in various parasite families, but none applying to all families. Our study uncovered no universal driver of parasite infection levels, even among parasite taxa from the same phylum, or with similar life cycles and transmission modes. Although local variables not considered here may have effects extending across taxa, our findings suggest the need for a taxon-specific approach in any attempt to predict disease dynamics and impacts in the face of environmental and climatic changes. [ABSTRACT FROM AUTHOR]

Recognizing the influence of pathogen diversity on infection dynamics is crucial for mitigating emerging infectious diseases. Characterising such diversity is often complex, for instance when multiple pathogen variants exist that interact differently with the environment and host. Here, we explore genotypic and phenotypic variation of Batrachochytrium salamandrivorans (Bsal), an emerging fungal pathogen that is driving declines among an increasing number of European amphibian species. For thirteen isolates, spanning most of the known temporal and geographical Bsal range in Europe, we mapped phenotypic diversity through numerous measurements that describe varying reproductive rates in vitro across a range of temperatures. Bsal isolates are revealed to have different thermal optima and tolerances, with phenotypic variation correlating with genomic diversity. Using a mechanistic niche model of the fire salamander (Salamandra salamandra) as an example, we illustrate how host steady-state body temperature and Bsal thermal range variation may influence pathogen growth through space and time across Europe. Our combined findings show how the identity of emergent pathogen variants may strongly influence when and which host populations are most at risk. Author summary: In 2013, a new, salamander-killing fungus, Batrachochytrium salamandrivorans (Bsal) was discovered in the Netherlands. Since then, Bsal outbreaks have occurred in a growing number of countries and amphibian species across Europe, causing rapid population collapses. A lot remains unknown about this pathogen, with most studies so far focusing on the type strain from the first outbreak site. Here we show that strains from other outbreaks behave differently and may threaten different amphibian populations at different times. We found that observed phenotypic variation correlated with genotypic variation and identified molecular functions and biological processes under selection across the European Bsal epidemic. As both the fungus and the amphibian hosts are very temperature sensitive, we tested Bsal growth across a range of temperatures. We found strains displayed different thermal ranges and optimal temperatures and combined these thermal growth curves with models of amphibian host body temperatures to predict strain geographical and temporal ranges. Our findings help to explain observed Bsal epidemiology and provide insights into how strain identity strongly influences when and which host populations are most at risk, with important implications for Bsal research and amphibian conservation efforts. [ABSTRACT FROM AUTHOR]

The decline of biodiversity, particularly among amphibians, is strongly associated with habitat loss and fragmentation. Vernal pools are a critical ecosystem for many pool‐breeding amphibians, but they are often overlooked in wetland protection guidelines. Mitigation efforts include vernal pool creation and restoration, but these efforts have varying success in replacing lost functions. This study investigates the success of created vernal pools through long‐term environmental monitoring of wood frogs and spotted salamanders (2014–2023) and integrates population genetics to assess the local population health of the wood frog. First, we monitored and compared environmental parameters and reproductive success of indicator species between natural and created pools in a Pennsylvania state park. We then used microsatellite loci to assess within‐ and between‐pool measures of genetic diversity, population structuring, and gene flow for wood frogs. We found two carefully designed created pools positively contributed to local amphibian population persistence by maintaining similar measures of genetic diversity as compared to natural pools. On the other hand, one poorly created pool was genetically distinct and acted as a population sink. Although our findings offer valuable insights, they are based on a limited sample and may not fully represent the broader landscape. However, by integrating genetic information into long‐term monitoring datasets, our interdisciplinary approach enhances our understanding of amphibian population dynamics in vernal pool ecosystems. Our findings imply that the most important factors for restoration practitioners to consider when creating or restoring vernal pools are hydroperiod (12–35 weeks), volume (> 50 m3), depth (≥ 30 cm), and surrounding forest land cover (> 60%). These variables are better predictors of indicator species success than pool type (i.e., natural or created). Ultimately, this study emphasizes the need to accompany restoration efforts with long‐term monitoring programs that can be used to make adaptive management decisions in an era of extreme environmental change. [ABSTRACT FROM AUTHOR]

Microbial assemblages naturally living on the skin are an integral part of immunity. In amphibians, this skin microbiota may hold a mitigation solution against the fungal pathogen Batrachochytrium dendrobatidis (Bd), which causes the panzootic disease chytridiomycosis. We used 16S rRNA gene metabarcoding to test the adaptive microbiome hypothesis. We compared the community composition, richness, and putative Bd‐inhibitory function of the skin microbiome of three amphibian host species in the Pyrenees, as well as three species in Taiwan, in both Bd‐positive and negative mountain populations. In both geographical regions, the amphibian host species played a decisive role in shaping the microbial assemblage and putative anti‐Bd properties. In the Pyrenees, the species most susceptible to chytridiomycosis, Alytes obstetricans, had the lowest relative abundances of putative protective bacteria. In Bd‐positive and negative sites, individuals had different skin microbiomes, with all anuran species showing increased relative abundances of potential anti‐Bd bacteria, while the Taiwanese caudata Hynobius sonani showed the opposite pattern. Our results suggest that, in response to exposure to the pathogen, the skin microbiota shifted to a defensive state with increased anti‐Bd function, which may contribute to promoting disease resistance, as proposed by the adaptive microbiome hypothesis. [ABSTRACT FROM AUTHOR]

Simple Summary: Age and size variation in widespread amphibians are often related to latitudinal or altitudinal temperature gradients. Species with toxic skin secretions, such as the fire salamander Salamandra salamandra, are an exception to the rule because their survival rates are relatively unaffected by predation, the major source of amphibian mortality. In contrast, average adult size varies greatly among populations, but variation is unrelated to geographical gradients. This study on four neighboring fire salamander populations inhabiting the catchments of low-order streams in the upper middle Rhine Valley (Koblenz, Germany) focuses on the identification of local environmental drivers of variation in age and body size distributions. I collected 192 individuals at two localities per stream, snout–vent length measured, clipped a toe for posterior skeletochronological age determination, and released salamanders in situ again. As expected, demographic parameters were in the range of other populations with an age at maturity of 2–3 years and a maximum lifespan of 17 years, but terrestrial habitat quality accounted for 3.6% of variation among populations. Variation in adult size resulted mainly from a carry-over effect of heavy metal contamination on juvenile growth rates. In conclusion, the average adult body size is a sensitive indicator of local habitat quality. Conspecific amphibian populations may vary widely in local demography and average body size throughout their geographical range. The environmental drivers of variation may reflect geographical gradients or local habitat quality. Among fire salamander populations (Salamandra salamandra), local demography shows a limited range of variation because high concentrations of skin toxins reduce mortality from predation to a minimum, whereas average adult body size varies significantly over a wide range. This study on four neighboring populations inhabiting the catchments of low-order streams in the upper middle Rhine Valley (Koblenz, Germany) focuses on the identification of local environmental drivers of variation in age and body size. I collected 192 individuals at two localities per stream, measured snout–vent length, clipped a toe for posterior skeletochronological age determination, and released salamanders in situ again. Populations were similar in age distribution. Local habitat quality accounted for a significant proportion of demographic variability, mediated by the impact of landscape-induced mortality risk, including roads and agriculture. Still, the main effect of variation in habitat quality was on adult body size, the result of growth rates of aquatic larvae and terrestrial juveniles. Larvae exposed to non-lethal heavy metal contamination in streams developed into smaller juveniles and adults than clean-water larvae, providing evidence for carry-over effects from one stage to another. The generally small average adult size in the Rhine Valley populations compared to those in other parts of the distribution range indicates the action of a still unidentified environmental driver. [ABSTRACT FROM AUTHOR]

Ranaviruses, members of the genus Ranavirus within the family Iridoviridae, have become a significant concern for amphibian populations globally, along with other cold‐blooded vertebrates, due to their emergence as a significant threat. We employed bioinformatics tools to examine the codon usage patterns in 61 DNA pol genes from Ranavirus, Lymphocystivirus, Megalocytivirus, and two unclassified ranaviruses, as no prior studies had been conducted on this topic. The results showed a slight or low level of codon usage bias (CUB) in the DNA pol genes of Ranavirus. Relative synonymous codon usage (RSCU) analysis indicated that the predominant codons favored in Ranavirus DNA pol genes terminate with C or G. Correlation analysis examining nucleotide content, third codon position, effective number of codons (ENC), correspondence analysis (COA), Aroma values, and GRAVY values indicated that the CUB across DNA pol genes could be influenced by both mutation pressure and natural selection. The neutrality plot indicated that natural selection is the primary factor driving codon usage. Furthermore, the analysis of the codon adaptation index (CAI) illustrated the robust adaptability of Ranavirus DNA pol genes to their hosts. Analysis of the relative codon deoptimization index (RCDI) suggested that Ranavirus DNA pol genes underwent greater selection pressure from their hosts. These findings will aid in comprehending the factors influencing the evolution and adaptation of Ranavirus to its hosts. [ABSTRACT FROM AUTHOR]

The effectiveness of acyclovir, a selective anti-herpesvirus agent, was tested both in silico and in vitro against two ranaviruses, namely the European catfish virus (ECV) and Frog virus 3 (FV3). ECV can cause significant losses in catfish aquaculture, while FV3 poses a risk to vulnerable amphibian populations. The genome of ranaviruses encodes thymidine kinases (TKs) similar to those of herpesviruses. Molecular docking simulations demonstrated that the acyclovir molecule can bind to the active sites of both investigated viral TKs in an orientation conducive to phosphorylation. Subsequently, the antiviral effect of acyclovir was tested in vitro in Epithelioma Papulosum Cyprini (EPC) cells with endpoint titration and qPCR. Acyclovir was used at a concentration of 800 µM, which significantly reduced the viral loads and titers of the ranaviruses. A similar reduction rate was observed with Ictalurid herpesvirus 2, which was used as a positive control virus. These promising results indicate that acyclovir might have a wider range of uses; besides its effectiveness against herpesviruses, it could also be used against ranavirus infections. [ABSTRACT FROM AUTHOR]

Accurately estimating effective population size (Ne) is essential for understanding evolutionary processes and guiding conservation efforts. This study investigates Ne estimation methods in spatially structured populations using a population of moor frog (Rana arvalis) as a case study. We assessed the behaviour of Ne estimates derived from the linkage disequilibrium (LD) method as we changed the spatial configuration of samples. Moor frog eggs were sampled from 25 breeding patches (i.e., separate vernal ponds, ditches or parts of larger fens) within a single population, revealing an isolation‐by‐distance pattern and a local spatial genetic structure. Varying buffer sizes around each patch were used to examine the impact of sampling window size on the estimation of effective number of breeders (Nb). Our results indicate a downward bias in LD Nb estimates with increasing buffer size, suggesting an underestimation of Nb. The observed bias is attributed to LD resulting from including genetically divergent individuals (mixture‐LD) confounding LD due to drift. This emphasises the significance of considering even subtle spatial genetic patterns. The implications of these findings are discussed, emphasising the need to account for spatial genetic structure to accurately assess population viability and inform conservation efforts. This study contributes to our understanding of the challenges associated with Ne estimation in spatially structured populations and underscores the importance of refining methodologies to address population‐specific spatial dynamics for effective conservation planning and management. [ABSTRACT FROM AUTHOR]

One of the major factors driving the currently ongoing biodiversity crisis is the anthropogenic spread of infectious diseases. Diseases can have conspicuous consequences, such as mass mortality events, but may also exert covert but similarly severe effects, such as sex ratio distortion via sex‐biased mortality. Chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd) is among the most important threats to amphibian biodiversity. Yet, whether Bd infection can skew sex ratios in amphibians is currently unknown, although such a hidden effect may cause the already dwindling amphibian populations to collapse. To investigate this possibility, we collected common toad (Bufo bufo) tadpoles from a natural habitat in Hungary and continuously treated them until metamorphosis with sterile Bd culture medium (control), or a liquid culture of a Hungarian or a Spanish Bd isolate. Bd prevalence was high in animals that died during the experiment but was almost zero in individuals that survived until the end of the experiment. Both Bd treatments significantly reduced survival after metamorphosis, but we did not observe sex‐dependent mortality in either treatment. However, a small number of genotypically female individuals developed male phenotype (testes) in the Spanish Bd isolate treatment. Therefore, future research is needed to ascertain if larval Bd infection can affect sex ratio in common toads through female‐to‐male sex reversal. [ABSTRACT FROM AUTHOR]

Understanding the effect of environmental factors on population characteristics of amphibians is crucial for their conservation and management. This is especially pertinent in regions vulnerable to climate change, such as the Qinghai–Tibetan Plateau (QTP). Here, we investigated the underlying environmental factors affecting the occurrence and abundance of Tibetan frogs (Nanorana pleskei) in the Three-River-Source region (TRSR) on the QTP. We found that N. pleskei is predominantly located in the headwater region of the Lancang River, with an increasing population size from northwest to southeast across the TRSR. Temperature oscillation acts as an ecological filter to determine the occurrence pattern, whereas the abundance is jointly influenced by maximum monthly temperature and precipitation and precipitation variability. Our study presents up-to-date information on the distribution and population status of N. pleskei in the hinterland of the QTP, which can assist conservation practitioners in developing effective management plans. Furthermore, our findings can contribute to the understanding of the distribution and abundance of amphibians within challenging high-elevation and plateau environments, offering insights that are valuable for the conservation and management of other amphibian species inhabiting similar high-elevation regions. [ABSTRACT FROM AUTHOR]

The Fundão dam collapse in 2015 resulted in the largest environmental disaster in Brazil's history with the release of tons of ore tailings mainly in aquatic environments. Amphibians are susceptible to contamination and they typically develop in aquatic and terrestrial habitats, making them useful indicators of environmental impact. Nonetheless, the effects of mining on amphibians are much overlooked compared with other waterborne organisms. We examined the impact of the disaster on the generalist treefrog Boana albopunctata (Spix, 1824) by measuring fluctuating asymmetry (FA) and liver mass in specimens collected in southeastern Brazil, before the disaster (2014) and at two time points after (2018 and 2022). Specimens collected in 2022 had lower FA levels in their tympanic area, which indicates the selection of individuals with more symmetrical eardrums across generations. We found liver hypertrophy after the accident, indicating the resilience of this biotransformative organ after heavy metal exposure but with likely physiological damage. This study is the first to demonstrate the impact of the Fundão dam rupture on an amphibian population living in the affected area. Our findings highlight the diverse impacts of mining on organisms and suggest that studies with amphibians can contribute in comprehending the magnitude of this and similar disasters. [ABSTRACT FROM AUTHOR]

Global climate change is expected to have a profound effect on species distribution. Due to the temperature constraints, some narrow niche species could shift their narrow range to higher altitudes or latitudes. In this study, we explored the correlation between species traits, genetic structure, and geographical range size. More specifically, we analyzed how these variables are affected by differences in fundamental niche breadth or dispersal ability in the members of two sympatrically distributed stream‐dwelling amphibian species (frog, Quasipaa yei; salamander, Pachyhynobius shangchengensis), in Dabie Mountains, East China. Both species showed relatively high genetic diversity in most geographical populations and similar genetic diversity patterns (JTX, low; BYM, high) correlation with habitat changes and population demography. Multiple clustering analyses were used to disclose differentiation among the geographical populations of these two amphibian species. Q. yei disclosed the relatively shallow genetic differentiation, while P. shangchengensis showed an opposite pattern. Under different historical climatic conditions, all ecological niche modeling disclosed a larger suitable habitat area for Q. yei than for P. shangchengensis; these results indicated a wider environment tolerance or wider niche width of Q. yei than P. shangchengensis. Our findings suggest that the synergistic effects of environmental niche variation and dispersal ability may help shape genetic structure across geographical topology, particularly for species with extremely narrow distribution. [ABSTRACT FROM AUTHOR]

Batrachochytrium dendrobatidis (Bd) is a pathogenic chytrid fungus that is particularly lethal for amphibians. Bd can extirpate amphibian populations within a few weeks and remain in water in the absence of amphibian hosts. Most efforts to determine Bd presence and quantity in the field have focused on sampling hosts, but these data do not give us a direct reflection of the amount of Bd in the water, which are useful for parameterizing disease models, and are not effective when hosts are absent or difficult to sample. Current methods for screening Bd presence and quantity in water are time, resource, and money intensive. Here, we developed a streamlined method for detecting Bd in water with low turbidity (e.g., water samples from laboratory experiments and relatively clear pond water from a natural lentic system). We centrifuged water samples with known amounts of Bd to form a pellet and extracted the DNA from that pellet. This method was highly effective and the resulting concentrations across all tested treatments presented a highly linear relationship with the expected values. While the experimentally derived values were lower than the inoculation doses, the values were highly correlated and a conversion factor allows us to extrapolate the actual Bd concentration. This centrifuge-based method is effective, repeatable, and would greatly expand the domain of tractable questions to be explored in the field of Bd ecology. Importantly, this method increases equity in the field, because it is time- and cost-efficient and requires few resources. [ABSTRACT FROM AUTHOR]

Chemical pollution, land cover change, and climate change have all been established as important drivers of amphibian reproductive success and phenology. However, little is known about the relative impacts of these anthropogenic stressors, nor how they may interact to alter amphibian population dynamics. Addressing this gap in our knowledge is important, as it allows us to identify and prioritise the most needed conservation actions. Here, we use long-term datasets to investigate landscape-scale drivers of variation in the reproductive success and phenology of UK Common frog (Rana temporaria) populations. Consistent with predictions, we found that increasing mean temperatures resulted in earlier initialisation of spawning, and earlier hatching, but these relationships were not consistent across all sites. Lower temperatures were also linked to increased spawn mortality. However, temperature increases were also strongly correlated with increases in urban area, arable area, and nitrate levels in the vicinity of spawning grounds. As with spawning and hatching, there was marked spatial variation in spawn mortality trends, where some sites exhibited steady increases over time in the proportion of dead or diseased spawn. These findings support previous work linking warming temperatures to shifts in timing of amphibian breeding, but also highlight the importance of assessing the effect of land use change and pollution on wild amphibian populations. These results have implications for our understanding of the response of wild amphibian populations to climate change, and the management of human-dominated landscapes for declining wildlife populations. [ABSTRACT FROM AUTHOR]

Remotely sensed measures of vegetation structure have been shown to explain patterns in the occurrence and diversity of several animal taxa, including birds, mammals, and invertebrates. However, very little research in this area has focused on reptiles and amphibians (herpetofauna). Moreover, most remote sensing studies on animal–habitat associations have relied on airborne or satellite data that provide coverage over relatively large areas but may not have the resolution or viewing angle necessary to measure vegetation features at scales that are meaningful to herpetofauna. Here, we combined terrestrial laser scanning (TLS), unmanned aerial vehicle laser scanning (ULS), and fused (FLS) data to provide the first test of whether vegetation structural attributes can help explain variation in herpetofauna abundance, species richness, and diversity across a woodland landscape. We identified relationships between the abundance and diversity of herpetofauna and several vegetation metrics, including canopy height, skewedness, vertical complexity, volume of vegetation, and coarse woody debris. These relationships varied across species, groups, and sensors. ULS models tended to perform as well or better than TLS or FLS models based on the methods we used in this study. In open woodland landscapes, ULS data may have some benefits over TLS data for modeling relationships between herpetofauna and vegetation structure, which we discuss. However, for some species, only TLS data identified significant predictor variables among the LiDAR‐derived structural metrics. While the overall predictive power of models was relatively low (i.e., at most R2 = 0.32 for ULS overall abundance and R2 = 0.32 for abundance at the individual species level [three‐toed skink (Chalcides striatus)]), the ability to identify relationships between specific LiDAR structural metrics and the abundance and diversity of herpetofauna could be useful for understanding their habitat associations and managing reptile and amphibian populations. [ABSTRACT FROM AUTHOR]

The decline in amphibian populations in recent decades may be linked to the occurrence of infectious diseases such as chytridiomycosis, which is caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd). It is known that symbiotic bacteria protect the host due to their inhibitory nature. However, how the population dynamics of amphibians is affected by additional effects provided by symbiotic bacteria has not been analyzed in depth. In this paper, a model is proposed to describe the interaction among susceptible amphibians, susceptible amphibians with symbiotic bacteria and amphibians with chytrid fungus. When the modeling takes into account the additional reproductive benefits that the symbiont Pseudomonas sp. grants to the host, multiple endemic equilibrium points can exist if R0 < 1 (R0 is the basic reproduction number for Bd). In this scenario, the existence of a subcritical bifurcation at R0 = 1, which can occur in two different disease-free equilibrium points, gives rise to complex dynamics and stability scenarios. Particularly, the analysis of the model shows that a sudden increase of fungus-infected amphibians can occur even when R0 < 1 due to bistability phenomena. In this scenario, the existence of a subcritical bifurcation, which translates for the fungus into colonization even for values of R0 less than one, represents an advantage for the chytrid fungus Batrachochytrium dendrobatidis since the pathogen should benefit from remaining as close as possible to an endemic equilibrium. To control the fungal infection, R0 must be reduced to a value below one until the endemic equilibrium points disappear. Finally, we show that the amphibian population can reach a critical population level close to an extinction scenario when R0 increases. [ABSTRACT FROM AUTHOR]

Persistent organic pollutants pose a great threat to amphibian populations, but information on the bioaccumulation of contaminants in amphibians remains scarce. To examine the tissue distribution and maternal transfer of organic halogenated pollutants (OHPs) in frogs, seven types of tissues from black‐spotted frog (muscle, liver, kidney, stomach, intestine, heart, and egg) were collected from an e‐waste–polluted area in South China. Among the seven frog tissues, median total OHP concentrations of 2.3 to 9.7 μg/g lipid weight were found (in 31 polychlorinated biphenyl [PCB] individuals and 15 polybrominated diphenyl ether [PBDE], dechlorane plus [syn‐DP and anti‐DP], bexabromobenzene [HBB], polybrominated biphenyl] PBB153 and ‐209], and decabromodiphenyl ethane [DBDPE] individuals). Sex‐specific differences in contaminant concentration and compound compositions were observed among the frog tissues, and eggs had a significantly higher contaminant burden on the whole body of female frogs. In addition, a significant sex difference in the concentration ratios of other tissues to the liver was observed in most tissues except for muscle. These results suggest that egg production may involve the mobilization of other maternal tissues besides muscle, which resulted in the sex‐specific distribution. Different parental tissues had similar maternal transfer mechanisms; factors other than lipophilicity (e.g., molecular size and proteinophilic characteristics) could influence the maternal transfer of OHPs in frogs. Environ Toxicol Chem 2024;43:1557–1568. © 2024 SETAC [ABSTRACT FROM AUTHOR]

Active forms of cannibalism that involve predation of live conspecifics occur widely among amphibians, most notably by tadpoles that feed on each other and adults that feed on juveniles. In contrast, cannibalism among amphibian adults (adult–adult cannibalism) is less often reported and there have been no investigations on the occurrence of sexual cannibalism in this group to date. In this study, we present an observation of potential sexual cannibalism involving an adult female green and golden bell frog, Litoria aurea, preying on a conspecific adult male during the species' breeding season. By comparing our observation to the available literature, we show that adult–adult cannibalism among amphibians is rare but tends to be committed by females against their male counterparts. We thus suggest that the occurrence of sexual cannibalism should be extended to include this group, where sexual size dimorphism occurs widely among adults that congregate spatially during breeding periods, both predictors of intra‐specific predation. We hypothesise that amphibian females may be able to exploit male advertisement calls to differentiate suitable partners from potential prey and that male individuals are vulnerable to sexual cannibalism as they must risk attracting and physically exposing themselves to females in order to reproduce. Our findings reveal the complex dynamics that exist within adult amphibian populations, suggesting that females may have a choice when deciding how to interact with and utilise their male counterparts. As our findings are preliminary, based on a small sample size of records, including several from captive individuals, we encourage authors to publish their observations of cannibalism in the field, including unsuccessful attempts, to confirm the presence of sexual cannibalism in this group. [ABSTRACT FROM AUTHOR]

Amphibian populations, including those of lungless salamanders (Plethodontidae), are susceptible to population declines, especially considering current and predicted climate change. Like many organisms, plethodontid salamanders exhibit reproductive plasticity to maximize population growth in response to environmental conditions. A better understanding of the external causes of reproductive plasticity can provide more accurate population models through the explicit incorporation of such drivers. To this end, we sampled Southern Pygmy Salamanders (Desmognathus wrighti) along a 1345-m elevational gradient in Great Smoky Mountains National Park, USA, to determine the effects of body size and elevation on reproductive investment. Using Bayesian mixed effects models, we assessed whether body size, elevation, or a combination of these factors best explained the probability an individual was gravid, the number of ova in gravid females, and the number of testis lobes in mature males. We found that the interaction of body size and elevation best explained each reproductive measure. Larger females were generally more likely to be gravid, with annual reproduction in fully mature females at low to mid-elevations and roughly biennial reproduction at high elevations. We also found a positive relationship between body size and ova counts at low and mid-elevations, but despite a reduction in reproductive frequency at higher elevations, we found no effect of body size on ova count. In addition, the addition of testis lobes, which has commonly been used as a proxy of age in plethodontid salamanders, occurred at larger body sizes with increasing elevation. Our findings support previous work showing a relationship between body size and reproductive ecology in desmognathine salamanders while providing insight into the complexity of this relationship in the context of elevational clines. Reproductive ecology significantly influences population dynamics; thus, further refinement of these observed patterns and their underlying causes is necessary to advance plethodontid salamander population ecology. [ABSTRACT FROM AUTHOR]

Effective population size (Ne) is a particularly useful metric for conservation as it affects genetic drift, inbreeding and adaptive potential within populations. Current guidelines recommend a minimum Ne of 50 and 500 to avoid short‐term inbreeding and to preserve long‐term adaptive potential respectively. However, the extent to which wild populations reach these thresholds globally has not been investigated, nor has the relationship between Ne and human activities. Through a quantitative review, we generated a dataset with 4610 georeferenced Ne estimates from 3829 populations, extracted from 723 articles. These data show that certain taxonomic groups are less likely to meet 50/500 thresholds and are disproportionately impacted by human activities; plant, mammal and amphibian populations had a <54% probability of reaching N̂e = 50 and a <9% probability of reaching N̂e = 500. Populations listed as being of conservation concern according to the IUCN Red List had a smaller median N̂e than unlisted populations, and this was consistent across all taxonomic groups. N̂e was reduced in areas with a greater Global Human Footprint, especially for amphibians, birds and mammals, however relationships varied between taxa. We also highlight several considerations for future works, including the role that gene flow and subpopulation structure plays in the estimation of N̂e in wild populations, and the need for finer‐scale taxonomic analyses. Our findings provide guidance for more specific thresholds based on Ne and help prioritise assessment of populations from taxa most at risk of failing to meet conservation thresholds. [ABSTRACT FROM AUTHOR]

The pathogenic fungus Batrachochytrium dendrobatidis has caused declines of amphibians worldwide. Yet our understanding of how water quality influences fungal pathogenicity is limited. Here, we reviewed experimental studies on the effect of water quality on this pathogen to determine which parameters impacted disease dynamics consistently. The strongest evidence for protective effects is salinity which shows strong antifungal properties in hosts at natural levels. Although many fungicides had detrimental effects on the fungal pathogen in vitro, their impact on the host is variable and they can worsen infection outcomes. However, one fungicide, epoxiconazole, reduced disease effects experimentally and likely in the field. While heavy metals are frequently studied, there is weak evidence that they influence infection outcomes. Nitrogen and phosphorous do not appear to impact pathogen growth or infection in the amphibian host. The effects of other chemicals, like pesticides and disinfectants on infection were mostly unclear with mixed results or lacking an in vivo component. Our study shows that water chemistry does impact disease dynamics, but the effects of specific parameters require more investigation. Improving our understanding of how water chemistry influences disease dynamics will help predict the impact of chytridiomycosis, especially in amphibian populations affected by land use changes. [ABSTRACT FROM AUTHOR]

Amphibians can obtain their colour from a combination of several different pigment and light reflecting cell types called chromatophores, with defects in one or several of the cells leading to colour abnormalities. There is a need for better recording of colour abnormalities within wild amphibian populations, as this may provide baseline data that can be used to determine changes in environmental conditions and population dynamics, such as inbreeding. In this study, we provide records of several types of chromatophore deficiencies, including those involving iridophores, xanthophores and melanophores, among two Australian tree frog species; the green and golden bell frog, Litoria aurea, and the eastern dwarf tree frog, L. fallax. We explore these colour abnormalities in terms of the chromatophores that have likely been affected and associated with their expression, in combination with typical colour phenotypes, colour variations and colour changes for these species. We intend for our photographs to be used as a visual guide that addresses the need for more accessible information regarding the physical manifestation of different chromatophore defects among amphibians. [ABSTRACT FROM AUTHOR]

Frog virus 3 (FV3) in the genus Ranavirus of the family Iridoviridae causes mass mortality in both anurans and urodeles worldwide; however, the phylogenetic origin of FV3-like ranaviruses is not well established. In Asia, three FV3-like ranaviruses have been reported in farmed populations of amphibians and reptiles. Here, we report the first case of endemic FV3-like ranavirus infections in the Korean clawed salamander Onychodactylus koreanus, caught in wild mountain streams in the Republic of Korea (ROK), through whole-genome sequencing and phylogenetic analysis. Two isolated FV3-like ranaviruses (Onychodactylus koreanus ranavirus, OKRV1 and 2) showed high similarity with the Rana grylio virus (RGV, 91.5%) and Rana nigromaculata ranavirus (RNRV, 92.2%) but relatively low similarity with the soft-shelled turtle iridovirus (STIV, 84.2%) in open reading frame (ORF) comparisons. OKRV1 and 2 formed a monophyletic clade with previously known Asian FV3-like ranaviruses, a sister group of the New World FV3-like ranavirus clade. Our results suggest that OKRV1 and 2 are FV3-like ranaviruses endemic to the ROK, and RGV and RNRV might also be endemic strains in China, unlike previous speculation. Our data have great implications for the study of the phylogeny and spreading routes of FV3-like ranaviruses and suggest the need for additional detection and analysis of FV3-like ranaviruses in wild populations in Asian countries. [ABSTRACT FROM AUTHOR]

Body size variation is central in the evolution of life‐history traits in amphibians, but the underlying genetic architecture of this complex trait is still largely unknown. Herein, we studied the genetic basis of body size and fecundity of the alternative morphotypes in a wild population of the Greek smooth newt (Lissotriton graecus). By combining a genome‐wide association approach with linkage disequilibrium network analysis, we were able to identify clusters of highly correlated loci thus maximizing sequence data for downstream analysis. The putatively associated variants explained 12.8% to 44.5% of the total phenotypic variation in body size and were mapped to genes with functional roles in the regulation of gene expression and cell cycle processes. Our study is the first to provide insights into the genetic basis of complex traits in newts and provides a useful tool to identify loci potentially involved in fitness‐related traits in small data sets from natural populations in non‐model species. [ABSTRACT FROM AUTHOR]

Applications of environmental DNA (eDNA) analysis methods for biomonitoring have grown exponentially over the last decade and provide a wealth of new information on the distribution of species. However, eDNA methods have limited application for estimating population‐level metrics. Environmental RNA (eRNA) has the potential to address ecological questions by gathering population demographic information from environmental media but may be challenging to detect and analyze. We developed gene‐specific eRNA assays targeting keratin‐associated genes in two focal species, American bullfrogs (Lithobates catesbeianus) and tiger salamanders (Ambystoma mavortium) to answer an important question in amphibian management: whether species detections represent breeding populations versus transitory adults. We performed an extensive laboratory validation with amphibians housed across development stages, where we collected 95 and 127 environmental samples for bullfrogs and salamanders, respectively. Both assays were highly specific to the larval stage and amplified with high sensitivity (90% in bullfrog and 88.4% in tiger salamander samples). We then applied our validated assays to multiple natural systems. When larvae were present, we found 74.1% overall detection in bullfrog field samples and 70.8% and 48.5% overall detection in field samples from ponds with A. macrodactylum and A. californiense larvae, correlating with eDNA detection rates. When only adults were present, we did not detect larvae‐specific eRNA in A. macrodactylum ponds, despite high eDNA detection rates. Although much work is ahead for optimizing assay design, sampling and filtering methods, we demonstrate that eRNA can successfully be used to discern life stages with direct application for ecology and conservation management. see also the Perspective by Robert M. Hechler and Melania E. Cristescu [ABSTRACT FROM AUTHOR]

• We provide planners, experts, and policy makers with habitat suitability maps for the terrestrial habitat of 11 amphibian species based on multi-scale species distribution models. • Potential dispersal routes between breeding ponds, validated with landscape genetic data. • Nationwide map of agricultural parcels near breeding ponds and along potential dispersal routes between breeding ponds where the potential for PPP-exposure exists. Plant protection products (PPPs) are among the many drivers that lead to the loss of biodiversity in agricultural landscapes and they are a contributing factor to the global decline of amphibians. The aim of the present study is to estimate the potential exposure of amphibian population networks to PPPs. Specifically, our goal is to describe the spatial overlap of amphibian population networks with agricultural crops where PPPs are potentially used. We estimate terrestrial habitat suitability for eleven amphibian species using a multi-scale species distribution modelling approach. Using the suitability maps as the basis for estimating landscape resistance, we then calculate potential dispersal corridors between known breeding sites for each species. Where available, we use local landscape genetic studies from the literature to validate and select the most appropriate resistance model for each species. By comparing the locations of suitable habitat and dispersal corridors with a parcel-scale database on agricultural land-use, we locate and quantify potential hotspots for PPP-exposure within the core habitat around each species' breeding sites and along the movement routes between them. By highlighting differences among species, we identify species which are particularly at risk of exposure and gain insight into the mechanisms with which PPPs in terrestrial habitats may potentially influence these networks. Together, the maps provide policy makers with a flexible tool that can identify and prioritize regions for the implementation of locally adapted management strategies. [ABSTRACT FROM AUTHOR]

Disease monitoring of amphibian assurance populations is an important buffer against ongoing global extinctions. This study documents a high incidence of neoplasia in a zoo-managed assurance population of Puerto Rican crested toads (Peltophryne lemur ; PRCTs). Over 5 years, neoplasia was diagnosed in 17/49 (35%) submitted adult PRCTs and was the cause of death or euthanasia in 13/17 (72%). Most toads were male (16/17; 94%) and 6 to 11-years-old (average 8.1 years). Notably, seven toads (41%) had multiple neoplasms. Of the 29 neoplasms identified, 17 (59%) were cutaneous or subcutaneous. The most common neoplasms included mast cell tumors (MCTs; 8/29; 28%), histiocytic sarcomas (6/29; 21%), lymphoma/leukemia (4/29; 14%), and squamous cell carcinomas (3/29; 10%). Distant metastases were documented in 6/8 (75%) toads with MCTs. Causes for neoplasia in this population were not determined though may include genetic or environmental factors. Continued investigations of managed endangered amphibians will help elucidate mechanisms of carcinogenesis. [ABSTRACT FROM AUTHOR]

Species Distribution Models have emerged in recent decades as a powerful tool for biodiversity research, as they allow, for example, assessing the status of species in their whole distributions. These models have been particularly helpful in demonstrating that amphibian populations are at high risk, with many declining and others already extinct. Here, we assessed the potential distribution of the helmeted water toad (Calyptocephalella gayi), an endemic Chilean amphibian considered a living fossil and cataloged as vulnerable, which requires significant conservation efforts. We modeled the species' potential distribution using the Maximum Entropy (Maxent) approach and determined the overlap with national protected areas. In addition, we conducted a geospatial risk analysis to estimate the threat level to which this toad is being subjected. The potential distribution of C. gayi ranges from 28°S to 44°S, mainly explained by altitude, mean diurnal temperature range, slope, and distance to water bodies. Protected areas only cover 3.55% of the species' potential geographic distribution, which is of concern, considering that the geospatial risk analysis showed that 60.61% of C. gayi's distribution is subjected to extreme and high risks. We discuss how these results are relevant to focusing and directing efficient protection and conservation efforts for this species shortly. [ABSTRACT FROM AUTHOR]

Controlled laboratory experiments are often performed on amphibians to establish causality between stressor presence and an adverse outcome. However, in the field, identification of lab-generated biomarkers from single stressors and the interactions of multiple impacts are difficult to discern in an ecological context. The ubiquity of some pesticides and anthropogenic contaminants results in potentially cryptic sublethal effects or synergistic effects among multiple stressors. Although biochemical pathways regulating physiological responses to toxic stressors are often well-conserved among vertebrates, different exposure regimes and life stage vulnerabilities can yield variable ecological risk among species. Here we examine stress-related biomarkers, highlight endpoints commonly linked to apical effects, and discuss differences in ontogeny and ecology that could limit interpretation of biomarkers across species. Further we identify promising field-based physiological measures indicative of potential impacts to health and development of amphibians that could be useful to anuran conservation. We outline the physiological responses to common stressors in the context of altered functional pathways, presenting useful stage-specific endpoints for anuran species, and discussing multi-stressor vulnerability in the larger framework of amphibian life history and ecology. This overview identifies points of physiological, ecological, and demographic vulnerability to provide context in evaluating the multiple stressors impacting amphibian populations worldwide for strategic conservation planning. [ABSTRACT FROM AUTHOR]

Horticulture poses a significant ecological risk, as agrochemicals are applied more frequently and in larger quantities per unit of production compared to extensive crop fields. The native amphibian Rhinella arenarum serves as a reliable bioindicator of environmental health. This study aimed to assess genocytotoxic damage and demographic life history traits of R. arenarum inhabiting horticultural environments. Sampling was conducted in suburban sites in central Argentina: H1 and H2 (sites associated with horticultural activity) and a reference site, RS. Environmental parameters were recorded, and the frequency of micronuclei (Mn), nuclear abnormalities (ENA), and indicators of cytotoxic damage were determined in tadpoles and adults. Demographic variables (age at maturity, longevity, potential reproductive lifespan, size at maturity, modal lifespan) were calculated. The highest nitrate and phosphate values, along with low dissolved oxygen values, were recorded at sites H1 and H2. Organisms inhabiting horticultural environments exhibited higher frequencies of Mn and ENA, surpassing those recorded in previous studies on tadpoles from sites with extensive crop production. Size at maturity and age at maturity of females, as well as size at maturity, longevity, mean age, and mean adult SVL of males, were lower in horticultural sites. The results support the hypothesis that anuran populations inhabiting horticultural environments demonstrate a diminished health status attributed to subpar environmental quality. Monitoring endpoints at different biological levels provides information on the ecotoxicological risk for amphibians and human populations inhabiting nearby areas. [ABSTRACT FROM AUTHOR]

Batrachochytrium dendrobatidis (Bd) is a lethal fungal species that parasitizes vertebrates and is associated with the worldwide decline of amphibian populations. The development of sensitive, rapid detection methods, particularly DNA-based techniques, is critical for effective management strategies. This study evaluates the efficacy of DNA extraction and a portable PCR device in a mountable field laboratory setup for detecting Bd near the habitats of three critically endangered Atelopus toad species in Ecuador. We collected skin swabs from Atelopus balios, A. nanay, and A. bomolochos, and environmental DNA (eDNA) samples from streams in Andean and coastal regions of Ecuador. For eDNA, a comparison was made with duplicates of the samples that were processed in the field and in a standard university laboratory. Our findings revealed Bd detection in eDNA and swabs from 6 of 12 water samples and 10 of 12 amphibian swab samples. The eDNA results obtained in the field laboratory were concordant with those obtained under campus laboratory conditions. These findings highlight the potential of field DNA-based monitoring techniques for detecting Bd in amphibian populations and their aquatic habitats, particularly in remote areas. Furthermore, this research aligns with the National Action Plan for the Conservation of Ecuadorian Amphibians and contributes to the global effort to control this invasive and deadly fungus. [ABSTRACT FROM AUTHOR]

Pool-breeding amphibians are reliant upon small, isolated, and fishless wetlands as sites for oviposition and larval development. These pools are often susceptible to impacts from anthropogenic disturbances, with off-road vehicle (ORV) trail development becoming an increasingly common form of wetland disturbance in the southwest Virginia coalfields. I performed a before-after control-impact (BACI) comparison of egg mass loss at 15 pools impacted and unimpacted by ORV trail development at a recently-opened public ORV trail system in Russell County, Virginia during the spring of 2024. Pools impacted by ORV use showed a mean 83% egg mass loss rate over just one week of trail use relative to no egg loss in unimpacted pools, with distinct mechanisms associated with ORV use (physical crushing, wheel-thrown eggs, and egg mass relocation) acting in concert to drive egg mass loss. My results provide some of the first empirical data documenting mechanisms of egg mass loss and embryonic mortality in poolbreeding amphibians from ORV disturbance and support several best management practices that land managers in Virginia and elsewhere can use to minimize impacts to resident amphibian populations on public and private lands managed for recreation. [ABSTRACT FROM AUTHOR]

Density dependent carry-over effects from one life history stage to another can affect the dynamics of populations. Here we study such carry-over effects from the tadpole to the postmetamorphic juvenile stage in an endangered amphibian, the natterjack toad (Epidalea calamita). We raised tadpoles in outdoor aquatic mesocosms at four densities and assessed juvenile performance after metamorphosis in terrestrial mesocosms. High larval density reduced mass at metamorphosis by 50 % and doubled the length of the larval period. Survival was reduced at the high densities. Larger metamorphs had higher survival in terrestrial mesocosms and remained larger than cohort members at the end of the 30-day experiment. Because juvenile survival drives amphibian population dynamics, density-dependent carry-over effects to the juvenile stage are likely to affect population viability. We discuss the implications of the results for amphibian conservation practice, both pond construction programs and surveys of amphibian populations. [ABSTRACT FROM AUTHOR]

Understanding how natural populations will respond to contemporary changes in climate is becoming increasingly urgent and of fundamental importance for the preservation of future biodiversity. Among vertebrates, amphibians and reptiles are more sensitive to environmental perturbations than endotherms and ectotherm diversity will likely be disproportionally impacted by climate change. Notwithstanding concerns surrounding the climate change resilience of ectotherm populations, accurately predicting future population trajectories based on contemporary ecological and physiological data alone remains challenging and much can be learnt by studying how populations have responded to climate change in the past. Genomic approaches can now assay the genetic diversity of contemporary population at an unprecedented scale but to date have been relatively underutilised when studying the demographic history of amphibians and reptiles. In this review, we first summarise how changing climatic conditions may influence the ectotherm phenotype and how this can translate to changes in fitness and population dynamics. We then discuss how the relative role of past climate in shaping ectotherm diversity has traditionally been approached in a phylogeographic context and how expanding genomic resources for ectotherm species can be leveraged to improve the study of past demography for many amphibian and reptilian groups. An integrative approach that links known proximate effects on phenotype due to climate change, with past changes in demographic trajectories will ultimately enable us to generate more accurate models of future population change and improve our ability to assess climate change resilience for many ectotherm groups. [ABSTRACT FROM AUTHOR]

Amphibians are disproportionately represented among the many vertebrate taxa that are declining globally. Few long-term studies of amphibians exist, especially in temperate climates, hindering our understanding of long-term trends in amphibian communities, which may delay or prevent management action. Here, we develop and deploy an inexpensive monitoring method with potentially broad scientific and community uptake, ‘rapid road surveys’. We test whether this protocol is useful in understanding relative abundance in an amphibian community over a 17-year period. From 2003 to 2019, we performed thousands of rapid (5–15 min) amphibian surveys and recorded the number of on-road amphibians along a single, 267 m stretch of secondary roads in rural Canada. Assuming that on-road occurrence reflects relative amphibian population sizes, we show that amphibians have declined by approximately 73% from 2003 to 2019. The decline was driven by a remarkable 91% decrease in the abundance of northern leopard frogs (Lithobates pipiens), the species comprising the most observation records, while all other species did not show a temporal trend. We cannot attribute a definitive mechanism to the L. pipiens decline. However, by ruling out a number of putative causes, we hypothesize that it may be related to land-use change or infectious disease. Our results show that a simple, temporally replicated road survey protocol, deployed in a spatially restricted area, can be a valuable tool for conservation scientists to understand trends in abundance across an entire community. We discuss how these rapid road surveys are likely a viable option for future community science initiatives. [ABSTRACT FROM AUTHOR]

The coexistence of multiple discrete color phenotypes (i.e. color polymorphism) has been studied in many diurnal species where environmental light allows most visual systems to chromatically discriminate color morphs. However, there is a large gap in our understanding of the discrimination thresholds and the function color polymorphisms play at night. We collected spectral data from the throats of red‐ and yellow‐morph males in a polymorphic population of the nocturnal amphibian Salamandra salamandra gallaica. We estimated the discriminability between morphs and their conspicuousness at night by fitting visual models of conspecifics and predators. We also collected morphological, behavioral and physiological data and assessed the abundance and activity patterns of each morph to explore their potential function. Visual models indicated that both conspecifics and predators can visually discriminate salamander color morphs under night‐light conditions. Assuming the potential role of yellow and red color patches as visual signals, putatively related to social signaling, we could suspect that these colors represent different adaptive optima. Red‐morph individuals had shorter bodies and lower body condition, but both morphs showed similar space use. In addition, both color morphs exhibited similar metabolic physiology, suggesting that the observed similarity in these traits may be better explained by the shared environmental conditions, rather than color. Finally, differences in the conspicuousness of red and yellow morphs could result in differential predation pressure. [ABSTRACT FROM AUTHOR]

Aim: Genetic diversity driven by natural selection contributes to population divergence in amphibians, thus facilitating local adaptation to climate change. Understanding the mechanisms of genetic adaptation is one of the important issues in evolutionary biology. This study set out to reveal drivers responsible for intraspecific divergence in Fejervarya multistriata and further investigate the potential involvement of selected genes in responding to climate challenges. Location: China. Method: To identify adaptive traits associated with climate change, we conducted genome RAD‐seq of 300 F. multistriata individuals from 15 locations across a bio‐geographical range with gradual climatic variation in China. Results: The results indicate a substantial genetic diversity among populations of F. multistriata and highlight specific genes and pathways that likely contribute to intraspecific divergence. The demographic history of F. multistriata can be traced back to the last interglacial period, during which elevated temperatures may have led to a significant decline in effective population size. The analysis of genome‐climate association identified five candidate genes (BMP2K, NRAP, ZW10, MYH1 and PLB1) potentially involved in local climate adaptation. Main Conclusions: Our findings have shed light on the genetic mechanisms of local adaptation to climate change in F. multistriata, thereby aiding in determining the possible fate of populations under future climate change. [ABSTRACT FROM AUTHOR]

Batrachochytrium dendrobatidis (Bd), a causative agent of chytridiomycosis, is decimating amphibian populations around the world. Bd belongs to the chytrid lineage, a group of early-diverging fungi that are widely used to study fungal evolution. Like all chytrids, Bd develops from a motile form into a sessile, growth form, a transition that involves drastic changes in its cytoskeletal architecture. Efforts to study Bd cell biology, development, and pathogenicity have been limited by the lack of genetic tools with which to test hypotheses about underlying molecular mechanisms. Here, we report the development of a transient genetic transformation system for Bd. We used electroporation to deliver exogenous DNA into Bd cells and detected transgene expression for up to three generations under both heterologous and native promoters. We also adapted the transformation protocol for selection using an antibiotic resistance marker. Finally, we used this system to express fluorescent protein fusions and, as a proof of concept, expressed a genetically encoded probe for the actin cytoskeleton. Using live-cell imaging, we visualized the distribution and dynamics of polymerized actin at each stage of the Bd life cycle, as well as during key developmental transitions. This transformation system enables direct testing of key hypotheses regarding mechanisms of Bd pathogenesis. This technology also paves the way for answering fundamental questions of chytrid cell, developmental, and evolutionary biology. [ABSTRACT FROM AUTHOR]

We studied the harlequin mantella along 18 transects from Fohisokina and Soamasaka during three different seasons of the year. Transects were installed in three dominant habitats at both sites. In total, we encountered the target species 62 times from all of our surveys. Several encountered animals vary between sites and seasons. No frog was observed during the winter. However, frog size is significantly different between sexes which females are larger than males. [ABSTRACT FROM AUTHOR]

The assessment of the health and protection of anuran amphibian populations in biotopes damaged by anthropogenic activity is today a priority and a global problem. The aim of this study is to determine the individual physical fitness of Pelophylax ridibundus individuals inhabiting a polluted area in Southern Bulgaria by calculating the scaled mass index (SMI) of frogs. We used frogs inhabiting a less disrupted habitat (less disturbed site) in order to make a comparison. Our working hypothesis was based upon the assumption that the two populations were expected to show differences in the values of the calculated scaled mass indices. That would allow us to assess how anthropogenic stress affects the individual body condition of frogs inhabiting a polluted area. A two-way ANOVA analysis revealed that there was a statistically significant interaction between the effects of site and sex on SMI. The simple main effects analysis showed that the site of origin alone has had a significant effect on SMI. In general, lower SMI values were indicative of deteriorated body fitness and suggested unfavorable environmental conditions. We found during this study that SMI can be discussed as a more accurate sex-independent discriminative marker for the habitat than the original unscaled SVL and BW parameters. [ABSTRACT FROM AUTHOR]

Long-time monitoring studies recently indicated that newts are in decline in many regions. Motivated by the above-mentioned, in the year 2019, we started monitoring the newt populations from the Jiu Gorge National Park (JGNP) in the Romanian Carpathians, 10 years after the previous study on the same topic. Compared with other areas where newts are in decline, we identified new distribution locations of the two newt species which are present in the park. Also, the previously known populations have greatly increased. Thus, the Lissotriton vulgaris population increased 2.58 times in 10 years, and the Triturus cristatus increased 1.80 times in 10 years. At the same time, in areas from JGNP affected by human activities in the past (abandoned quarry and areas adjacent to the railway), the newts extended their range in the last years and occupied artificial aquatic habitats. In the case of the populations from the natural habitat, the temporal dynamics and the ratio between sexes and species followed the same evolution as in the case of other populations from Romania. The increase of newt populations from JGNP in the last 10 years was most probably a consequence of the reduced human pressure, corroborated with the large surface occupied by native forests in the park. Thus, in natural areas, probably the best management measures for both newt species are not represented by direct (invasive) human interventions but by the conservation of the natural habitats used by the newts. A protected area should maintain the conservation status at least at the present level, and if the region is natural, this fact will maintain and also increase the newt and probably other amphibian populations. [ABSTRACT FROM AUTHOR]

Simple Summary: Threatened animal species live in small and isolated populations, often with a reduced number of individuals and reduced genetic diversity. In this review, we summarise studies on amphibian species that examined the effect of genetic diversity on the fitness of individuals or populations. We found evidence for the positive association between genetic diversity and different estimates of fitness where low genetic diversity is associated with lower fitness. Published studies are however scarce, concentrated on a handful species and with a high proportion of non-significant results reported. For the maintenance of amphibian and other animal populations, it is important to increase the research effort in this topic and, for imperilled populations, enhance genetic diversity through different types of conservation measures. Endangered animals suffer from isolation of their habitats. Isolation leads to a reduction in population size as well as a decrease in genetic diversity and a concomitant increase in the risk of extinction. Amphibians are the most endangered vertebrate class. Besides habitat loss, fragmentation and isolation, amphibians are threatened by emerging diseases e.g., chytrid fungus or Ranavirus. By employing experiments, researchers investigate whether changes in genetic diversity within or among isolated populations affect amphibian fitness. While genetic diversity estimates are based on molecular markers, typically microsatellites, fitness is mostly measured as tadpole performance in rearing experiments often under varying environmental conditions. Tadpole performances (e.g., body mass, growth rate and survival) have been found to be negatively affected by low genetic diversity, as several studies have found a positive association between genetic diversity and these fitness traits. Moreover, infection with pathogens also seems to be more likely in individuals or populations with lower genetic diversity. Overall, these genetic–fitness correlations seem to be more pronounced or detectable in smaller, declining populations but not in larger populations. Genomic studies, which sample a larger fraction of the genome, are still scarce in the conservation genetic literature on amphibians. These are likely to increase in upcoming years and may reveal adaptive variants that protect against dangerous pathogens or environmental changes. Altogether, genetic–fitness correlation studies should be a priority in order to develop effective management plans for the genetic rescue of isolated, imperilled amphibian populations. [ABSTRACT FROM AUTHOR]

Background: Mosquitoes are the deadliest organisms in the world, killing an estimated 750,000 people per year due to the pathogens they can transmit. Mosquitoes also pose a major threat to other vertebrate animals. Culex territans is a mosquito species found in temperate zones worldwide that feeds almost exclusively on amphibians and can transmit parasites; however, little is known about its ability to transmit other pathogens, including fungi. Batrachochytrium dendrobatidis (Bd) is a topical pathogenic fungus that spreads through contact. With amphibian populations around the world experiencing mass die-offs and extinctions due to this pathogen, it is critical to study all potential modes of transmission. Because Cx. territans mosquitoes are in contact with their hosts for long periods of time while blood-feeding, we hypothesize that they can transmit and pick up Bd. Methods: In this study, we first assessed Cx. territans ability to transfer the fungus from an infected surface to a clean one under laboratory conditions. We also conducted a surveillance study of Bd infections in frogs and mosquitoes in the field (Mountain Lake Biological station, VA, USA). In parallel, we determined Cx. territans host preference via blood meal analysis of field caught mosquitoes. Results: We found that this mosquito species can carry the fungus to an uninfected surface, implying that they may have the ability to transmit Bd to their amphibian hosts. We also found that Cx. territans feed primarily on green frogs (Rana clamitans) and bullfrogs (Rana catesbeiana) and that the prevalence of Bd within the frog population at our field site varied between years. Conclusions: This study provides critical insights into understanding the role of amphibian-biting mosquitoes in transmitting pathogens, which can be applied to disease ecology of susceptible amphibian populations worldwide. [ABSTRACT FROM AUTHOR]

Changes in the natural landscape and the indiscriminate use of pesticides can have a major impact on aquatic environments and have contributed to the worldwide decline of amphibian populations. In the present study, we sampled tadpoles of three anuran amphibians (Boana albopunctata, Physalaemus cuvieri, and Dendropsophus minutus) from ponds in six different agricultural landscapes of the Brazilian Cerrado savanna and evaluated whether and to what extent genotoxic and mutagenic damage was related to land use (the amount of forest and agricultural remnants, and related physicochemical factors) and the presence of pesticides in the water of the study ponds. We also evaluated the hepatotoxicity in P. cuvieri, which was the most abundant species at five of the six sampling points. Clomazone and atrazine were the most common pesticides found in the ponds. The B. albopunctata and P. cuvieri tadpoles presented similar patterns of DNA damage among the sampling points. The least DNA damage was found in the D. minutus tadpoles, although this species was present in only one of the study ponds. More binucleated and anucleated cells were observed in B. albopunctata, but there was no significant variation among species in terms of the number of micronuclei or other erythrocytic nuclear abnormalities. Land use and physicochemical factors did not explain the variation in the DNA damage observed in the three anurans. The hepatotoxicity analyses of P. cuvieri revealed the presence of a series of alterations, including the enlargement of the sinusoids, vacuolization of the hepatocytes, the infiltration of inflammatory cells, hepatic steatosis, and dilation of the blood vessels. The interaction between physicochemical factors and the biomarkers analyzed in the present study is complex. In particular, it will be important to better elucidate which factors are contributing, either directly or indirectly, to the decline of anuran amphibian populations, especially in threatened biomes, such as the Brazilian Cerrado. In this case, we would encourage further in situ studies that assess the ecotoxicology of the landscape, together with the systematic monitoring of aquatic environments, to guarantee the long‐term integrity of amphibian populations, and those of other organisms that play an essential functional role in the ecosystem. Environ Toxicol Chem 2023;42:2422–2439. © 2023 SETAC [ABSTRACT FROM AUTHOR]

The relationship between the thyroid gland and reproduction in amphibians and reptiles has been studied for more than 100 years. Most studies suggest a positive involvement of thyroid hormones with some aspects of reproduction, but some studies support a negative role for thyroid hormones at certain life stages. Comprehensive studies of gene activation/suppression by thyroid hormones and their absence at various levels of the hypothalamo–pituitary–gonadal axis coupled with observations of adrenocorticoid activity, reproductive performance, and metabolic involvement are needed to understand this complex relationship. Highlights: Most amphibian and reptilian populations are declining in the face of climate changes, pollution, and habitat destruction. Although the hypothalamo–pituitary–thyroid axis often is positively associated with reproduction in amphibians and reptiles, negative interactions also occur at some life stages and in some species. Comprehensive studies involving thyroid and adrenal activity and gene activation/repression linked with reproductive events are needed [ABSTRACT FROM AUTHOR]

Understanding how species respond to land transformation is an essential step toward the development of effective conservation policies. This is especially urgent in deforestation hotspots, and for those groups particularly sensitive to changes in land cover. However, the scarcity of data on population trends is among the most pervasive shortfalls in biodiversity knowledge, hampering the design of effective conservation. This deficiency is commonly addressed by comparing population sizes between natural and transformed land‐cover types. Here we mapped the global knowledge (and knowledge gaps) about changes in the abundance of amphibian and reptile populations in natural and transformed land cover, with an emphasis on deforestation hotspots. Notably, our results show that there is scant information even about this proxy of population trends. On average, data are absent for 75% of amphibians and 83% of reptiles within each grid cell worldwide. Moreover, such information is extremely rare for deforestation fronts, and that which does exist comes from populations external to these areas. Strategic investment to fill these data gaps, especially in deforestation hotspots, is a crucial step to guide conservation policy making. [ABSTRACT FROM AUTHOR]