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The trophic niche is one of the most important ecological traits for any species, providing information about trophic position in the food web, habitat preferences, and interspecific interactions. In this study, we describe the autumn diet of two sympatric species of salamander from central Italy—Italian Cave Salamanders (Speleomantes italicus) and Fire Salamanders (Salamandra salamandra), assessing whether competition for the same prey occurs. Furthermore, we combine our data with those obtained for the same population during a different season (spring) and assess potential seasonal variation in the diet of these two salamander species. The overlap of the trophic niche between the two species was limited, with S. italicus consuming smaller and fast-moving prey (e.g., Diptera, Collembola), and S. salamandra consuming slow and often elongated prey (e.g., Gastropoda, Haplotaxida, Diplopoda). Seasonal differences in diet composition were observed in both species between spring and autumn; in autumn, both species narrowed their trophic niche breadth. This seasonal divergence is likely due to the variation of prey phenology and availability. The consumption of prey of different size was likely the main factor allowing the coexistence of these two salamander species. In both species we observed a general increase in the proportion of generalist individuals in autumn, most likely because of a reduction in prey availability. In addition to providing information on the trophic niche of these species, our study represented a further step that helps unravel the dynamics promoting the coexistence of potentially competing species. [ABSTRACT FROM AUTHOR]

Since being described in the year 2000, little ecological information has accumulated for South Mountains Gray-Cheeked Salamanders (Plethodon meridianus), a narrowly distributed salamander in southern Appalachia. In this study, we used repeat surveys to model occupancy and abundance of P. meridianus along a transect running from the approximate range center to range edge. We found a strong effect of elevation and distance to streams as predictors of occupancy and abundance. The number of days since rain had a strong impact on detection probability, likely due to its effect on salamander surface activity (i.e., time outside of burrow), as opposed to observer error. Treating elevation as a proxy for distance to the range edge, we found that occupancy and abundance declined toward the range edge, supporting the center-periphery hypothesis. Our findings matched that of similar previous studies: at low elevations in dry habitat, salamanders are only found along the cooler microhabitat of streams, whereas at high elevations, salamanders are more widespread across the landscape. [ABSTRACT FROM AUTHOR]

Agonistic behavior, a critical component of territoriality, is widespread throughout terrestrial plethodontid salamanders, though geographic variation in this behavior is poorly understood. Using color polymorphic Eastern Red-backed Salamanders (Plethodon cinereus), we conducted same-sex laboratory trials to compare aggressive and submissive behaviors between two genetically distinct groups in northern Ohio. For each group, we tested 120 individuals from 3 populations. We predicted that the genetic group with a single color morph would exhibit a higher degree of agonistic and territorial behavior compared to the genetic group with two morphs as an adaptive consequence of altered social dynamics in monomorphic populations. Contrary to our prediction, laboratory trials demonstrated that residents from the polymorphic group were significantly more aggressive than residents from the monomorphic group. This finding was corroborated by a strong residency effect in the polymorphic group, an effect that was weaker in the monomorphic group. Our results suggest that individuals in the polymorphic group are more aggressive and territorial than individuals in the monomorphic group, signifying a greater propensity to secure a territory and defend it against intruders. Our results add important insight into how geographic variation and differences in morph frequency can be attributed to behavioral differences. [ABSTRACT FROM AUTHOR]

Studies of reproductive behavior can help reveal patterns of sexual isolation and clarify species boundaries. In northern Georgia, Blue Ridge Two-lined Salamanders (Eurycea cf. wilderae) and Brown-backed Salamanders (Eurycea aquatica) are syntopic but do not hybridize. Within this region, Eurycea cf. wilderae males exhibit a reproductive polymorphism, with "searching" males that appear adapted for terrestrial courtship and "guarding" males that appear adapted for aquatic mate-guarding. To understand better how inter- and intraspecific reproductive variation might contribute to sexual isolation between E. aquatica and E. cf. wilderae, we staged T-maze trials and courtship trials, and we conducted preliminary analyses of sex hormones from noninvasive fecal samples. We found that males of both species preferred conspecific female scents to heterospecific female scents, but that searching male E. cf. wilderae were not better than guarding males at locating a conspecific female scent. We also found evidence for strong propensity asymmetry, with male and female E. cf. wilderae much more likely than E. aquatica to engage in courtship behaviors in the lab. Still, we observed some instances of heterospecific courtship through spermatophore transfer. Finally, we found evidence for higher fecal testosterone concentrations in males than females and higher concentrations in guarding male than in searching male E. cf. wilderae. Together, our data provide further insight into the reproductive ecologies of and the nature of reproductive isolation between Eurycea aquatica and Eurycea cf. wilderae. [ABSTRACT FROM AUTHOR]

In May 2023, herpetologists from six countries converged at the 8th Conference on the Biology of Plethodontid Salamanders in Hammond, Louisiana to share their latest cutting-edge research. The conference was hosted by the Department of Biological Sciences at Southeastern Louisiana University. Dr. Richard Bruce was the honoree. The presentations covered a diverse array of topics from gene expression to behavior to speciation, illustrating the value of plethodontid salamander biology to a range of disciplines. This special issue of Herpetologica includes 16 papers highlighting a range of research on plethodontids and encouraging new approaches to tackle old and new questions. [ABSTRACT FROM AUTHOR]

The Cumberland Plateau Salamander, Plethodon kentucki, is a cryptic species with respect to the sympatric Northern Slimy Salamander, Plethodon glutinosus. It was first described by Highton and MacGregor (1983) by using allozyme data. In that description, the authors reported extreme levels of genetic differentiation for a single species with a narrow distribution; however, follow-up studies found patterns of genetic variation that were discordant with the allozyme data. In this paper, we describe patterns of genetic variation within P. kentucki by using an anchored hybrid enrichment dataset of 21 individuals sampled from across its known range. We identified four genetic groups with extensive admixture and isolation by distance. We constructed a population tree by using TreeMix and inferred gene flow between two of the four genetic groups. Finally, we used Bayesian phylogenetics and phylogeography (BPP) in conjunction with the genealogical divergence index (gdi) to test species boundaries within P. kentucki. Although BPP suggested that P. kentucki could be four species, gdi indicated that none of the groups were sufficiently independent to constitute separate species. We conclude that P. kentucki is best recognized as a single species with substantial genetic structure within its limited distribution. [ABSTRACT FROM AUTHOR]

In some populations of the Two-Lined Salamander (Eurycea bislineata) species complex, males exhibit two alternative reproductive tactics: "searching" and "guarding." Searching males have secondary sexual characters—including a large, pheromone-producing mental gland—used in terrestrial courtship, whereas guarding males have hypertrophied jaw musculature used in mate-guarding behavior near aquatic nesting sites. Although this polymorphism occurs in at least four evolutionarily distinct lineages, previous histological studies have only focused on soft-tissue differences in one of these species and no studies have evaluated osteological differences between alternative reproductive tactics. Herein, we present new histological and osteological data from three evolutionarily distinct lineages within the E. bislineata species complex. We confirmed that traditional mental glands are restricted to searching males and that caudal courtship glands are present in both male phenotypes, but not in females. We also found variation in other skin glands that warrants further investigation. Cleared and stained specimens and microcomputed tomography data both revealed substantial osteological differences in skull morphology. Compared with searching males, guarding males have increased skull ossification, fewer and larger teeth, and more pronounced otic and squamosal crests. Together, these data expand our knowledge of morphological differences between alternative reproductive tactics, and we discuss the implications of our results for hypotheses regarding phenotypic plasticity throughout the lifetime of an individual male. [ABSTRACT FROM AUTHOR]

Species are the fundamental unit of biodiversity studies. However, many species complexes are difficult to delimit, especially those characterized by complicated patterns of population structure. Salamanders in the family Plethodontidae often form species by slowly fragmenting across a landscape over space and time. They thus provide many examples of species complexes in which gradual Darwinian evolution has resulted in multiple units of varying degrees of differentiation, including incompletely separated lineages. Herein, we report on a molecular systematic investigation of woodland salamanders in the Plethodon wehrlei group, a group that has recently been split from two species into five species. To quantify patterns of genetic variation, we collected genetic samples from 24 individuals from 20 populations, including all species and representing a carefully selected subset of previous work. From these samples, we obtained genomic data by using anchored hybrid enrichment, resulting in 319 loci averaging 1300 bp in length. Biallelic single-nucleotide polymorphisms were randomly selected from 316 of these loci for some analyses. We examined patterns of genetic structure by using a combination of multivariate statistics and methods based on evolutionary models (such as the Bayesian program STRUCTURE) and found that all of the recognized species formed genetic clusters; however, P. wehrlei and P. punctatus were relatively weakly differentiated and STRUCTURE identified three separate clusters within P. jacksoni. Species trees inferred using the weighted accurate species tree algorithm (wASTRAL), Bayesian phylogenetics and phylogeography (BPP), and TreeMix all recovered the same topology, with P. dixi sister to the other taxa, which included a northern clade (P. wehrlei, P. punctatus, P. pauleyi) and a southern clade (P. jacksoni, with three separate groups). TreeMix only inferred one gene flow event. We evaluated the candidate species by using BPP and the genealogical divergence index (gdi). Although BPP delimited all candidate species with strong support (all posterior probabilities = 1.0), the gdi only strongly supported P. dixi and P. pauleyi, both of which have only been recently described. We discuss the difficult problem of species delimitation in groups that form species via range fragmentation. We also provide a vision for future research, with the aim of better testing and diagnosing the species diversity within the P. wehrlei group. [ABSTRACT FROM AUTHOR]

Male Ensatina eschscholtzii do not have a mental gland, a macrogland used by males during courtship that is considered an ancestral character of plethodontids. We tested whether males and females have nonmental courtship glands associated with the integument of the rostrum and mentum (chin). We found that both male and female E. eschscholtzii possess courtship-like integumentary glands (modified granular glands) in the upper labia extending dorsally along the rostrum and lower labia extending ventrally across the mental region. These glands are sexually dimorphic in size (larger in females) and react positively with periodic acid–Schiff. We hypothesize that these glands are involved in courtship through production of pheromones that may or may not be similar to pheromones produced in courtship glands of other plethodontid salamanders. These rostral glands are structurally and chemically unique in comparison with glands of the rostrum that empty along the length of nasolabial grooves (nasolabial glands) of Ensatina, which do not appear to be involved in pheromone production. Both females and males have relatively few traditional mucous glands throughout the skin in comparison with other species of plethodontids, although some clusters are identified at the anterior edges of the labia. [ABSTRACT FROM AUTHOR]

Accurate knowledge of species distributions is necessary for research and conservation. Slimy Salamanders (Plethodon glutinosus complex) are similar in appearance, tend toward small geographic ranges, and have a propensity for hybridization, necessitating genetic analysis and fine-scale sampling for accurate representation of species distributions. Our current understanding of the distributions of some Slimy Salamanders is based on coarse sampling. Several recent studies question the validity of some species, calling for more geographic and genetic sampling to confirm the species in this group and better define their distributions. Toward this, we analyzed the mitochondrial ND2 gene sequences of 434 individual Slimy Salamanders, 412 of which are from 294 localities west of the Mississippi River, USA. We also estimated ancestral ranges to better understand the biogeographic history underlying current species distributions. We found a much larger distribution for P. kiamichi than previously thought, including several contact zones with P. albagula. We confirmed the Ouachita River separates P. kisatchie and P. albagula in southern Arkansas. Texas P. albagula were not recovered as monophyletic, forming two distinct clades, one of which is nested within a large Interior Highlands (Ouachita and Ozark mountains) clade. Our data suggest P. sequoyah from the type locality have the introgressed mitochondria of P. albagula. We discovered three unnamed mitochondrial clades, one of which we hypothesize is nonintrogressed P. sequoyah. Our biogeographic analysis estimates multiple east–west dispersals across the Mississippi River and at least one west–east dispersal. With these findings, we have updated species distributions, identified contact zones and areas of potential contact, and revealed previously unknown evolutionary lineages. This information will be beneficial for further studies on this complex, which have thus far been hampered by unrefined species boundaries. Furthermore, this work has implications for revising the conservation ranks and management of western Slimy Salamanders. [ABSTRACT FROM AUTHOR]

Patterns of species distributions and abundance are driven by a combination of species abiotic niches and biotic interactions between members of a community. Joint-species distribution models extend traditional modeling of occurrence or abundance to quantify species corelationships that may result from interspecific interactions. In the southern Appalachian Mountains, stream-associated salamander communities are thought to be structured by competitive and predatory interactions; therefore, spatial patterns in occurrence and abundance and temporal patterns in activity may reflect species associations. To evaluate the role of interspecific interactions in salamander community occurrence and abundance patterns, we conducted repeated point-count and leaf-bag surveys for adult and larval communities, respectively. We estimated adult and larval community occurrence and abundance by using the hierarchical modeling of species communities framework to identify the extent to which residual co-occurrence and correlation in abundance was present within these communities. For both adult and larval communities, we found no evidence that residual co-occurrence or correlation in abundance was present. Instead, results indicated that environmental covariates characterizing both plot- and landscape-level habitat conditions were responsible for observed patterns. In addition, we found no evidence for temporal niche partitioning, suggesting competition does not play a significant role in inter- or intraday activity patterns. Our results contrast with the accepted paradigm that extant biotic interactions drive community composition among stream-associated salamanders. Instead, our findings suggest that the effects of biotic interactions are not evident at the spatial or temporal scales associated with occurrence or abundance. [ABSTRACT FROM AUTHOR]

Multispecies assemblages of Appalachian desmognathans have long intrigued ecologists seeking to understand the structure of ecological communities. Body size and life history in this group correlate with the moisture gradient from stream to forest, with large species being more aquatic and progressively smaller ones being ever more terrestrial. Since the work of N.G. Hairston, Sr. in the early 1980s, the prevailing hypothesis has been that predation and competition among desmognathans themselves have been the driving processes in the development and maintenance of the spatial organization along stream sides, with large, aggressive species forcing smaller ones to occupy less favorable terrestrial niches. Decades of research have confirmed that biotic interactions are important. However, evidence from recent studies has not agreed with the idea that biotic interactions are primary. Herein, I have concluded that the prevailing hypothesis fails to reconcile the currently available data. I have presented an alternative hypothesis that an abiotic factor, specifically the relative abundance of water, has been the primary force driving adaptation of species of Desmognathus longitudinally along moisture gradients by way of stream headwaters. Interspecific interactions, though important aspects of the current ecology of these species, are not the underlying drivers of spatial organization along the moisture gradient. I have further generated specific predictions that will enable this hypothesis to be tested. [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]

Headwater streams are critical, fragile ecosystems that supply food and nutrients for an array of organisms that are vital to the overall health of a stream. As the dominant vertebrates in headwater streams of the southern Appalachian Mountains, plethodontid salamanders are critical to healthy headwater communities. However, a neglected feature of these ecosystems is the community of parasites that infect salamanders. The digenetic trematode Metagonimoides oregonensis uses the aquatic snail Elimia proxima as its first intermediate host and the plethodontid salamander Desmognathus amphileucus as its second intermediate host. In a series of southern Appalachian streams, we tested the hypothesis that variance in the prevalence and intensity of infection in salamander hosts is related to respective densities of the snail and salamander species. Infection prevalence was 100% across all streams. There was a strong relationship between the density of the snail host and infection-intensity level in the salamander host. However, the relationship with salamander density was not important, a finding that conflicts with the results of parasitological studies involving lentic and marine systems. The influence of this trematode on the ecology of headwater streams and the resident salamanders has been underappreciated, and a number of aspects of this relationship remain unknown. [ABSTRACT FROM AUTHOR]

Amphibians are well-known for their ability to produce and secrete a mixture of bioactive substances in specialized skin glands for the purpose of antibiotic self-protection and defense against predators. Some of these secretions contain various small molecules, such as the highly toxic batrachotoxin, tetrodotoxin, and samandarine. For some time, the presence of peptides in amphibian skin secretions has attracted researchers, consisting of a diverse collection of – to the current state of knowledge – three to 104 amino acid long sequences. From these more than 2000 peptides many are known to exert antimicrobial effects. In addition, there are some reports on amphibian skin peptides that can promote wound healing, regulate immunoreactions, and may serve as antiparasitic and antioxidative substances. So far, the focus has mainly been on skin peptides from frogs and toads (Anura), eclipsing the research on skin peptides of the ca. 700 salamanders and newts (Caudata). Just recently, several novel observations dealing with caudate peptides and their structure-function relationships were reported. This review focuses on the chemistry and bioactivity of caudate amphibian skin peptides and their potential as novel agents for clinical applications. [ABSTRACT FROM AUTHOR]

Amphibians globally suffer from emerging infectious diseases like chytridiomycosis caused by the continuously spreading chytrid fungi. One is Batrachochytrium salamandrivorans (Bsal) and its disease ‒ the 'salamander plague' ‒ which is lethal to several caudate taxa. Recently introduced into Western Europe, long distance dispersal of Bsal, likely through human mediation, has been reported. Herein we study if Alpine salamanders (Salamandra atra and S. lanzai) are yet affected by the salamander plague in the wild. Members of the genus Salamandra are highly susceptible to Bsal leading to the lethal disease. Moreover, ecological modelling has shown that the Alps and Dinarides, where Alpine salamanders occur, are generally suitable for Bsal. We analysed skin swabs of 818 individuals of Alpine salamanders and syntopic amphibians at 40 sites between 2017 to 2022. Further, we compiled those with published data from 319 individuals from 13 sites concluding that Bsal infections were not detected. Our results suggest that the salamander plague so far is absent from the geographic ranges of Alpine salamanders. That means that there is still a chance to timely implement surveillance strategies. Among others, we recommend prevention measures, citizen science approaches, and ex situ conservation breeding of endemic salamandrid lineages. [ABSTRACT FROM AUTHOR]

We analyzed data from 3,546 occurrence records of Fire Salamanders (Salamandra salamandra) from the territory of the Czech Republic where it has a heterogeneous distribution pattern. Its occurrence in terrestrial habitats adjacent to breeding streams is characterized by a mean distance of 103 m, maximum 1,321 m, from the nearest stream. Based on a logistic GLM (generalized linear model) analysis we determined the Fire Salamanders' climatic and habitat associations at landscape scale in the Czech Republic. The main limiting factors for its dispersal include the proximity of small shallow streams in rolling landscapes, the pH of these streams, the presence of broad-leaf or mixed forests, humidity, solar irradiation, and severity of winters. While the absence of suitable breeding habitats is the main limiting factor for their occurrence in more expansive lowlands, factors such as lower temperatures, lower humidity, and the absence of broad-leaf and mixed forests begin to play a role with increasing altitude. Unlike cold temperatures, low amounts of precipitation and higher temperatures do not act as limiters in the Czech Republic. Fire Salamanders respond to the colder climate of higher altitudes with intensified summer activity and the purely bimodal nature of their activity (with spring and autumn peaks) tends to fade at higher altitudes. [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]

Co‐occurrence between species may be mediated by ecological differences or competitive interactions, but the nature of these interactions can vary across spatial scales. At coarse scales, species may appear to broadly co‐occur, but at fine scales, particularly for species with small home ranges, species may utilize different aspects of the microhabitat such that co‐occurrence is limited and competitive interactions are reduced or eliminated. We investigated the microhabitat use of two morphologically and ecologically similar woodland salamanders (the Red‐backed Salamander, Plethodon cinereus, and the Northern Ravine Salamander, P. electromorphus) that are distributed throughout the Alleghany Plateau in eastern North America to determine whether they partition habitat at finer scales. We also tested if P. electromorphus is a specialist on habitat types that allow it to exclude P. cinereus, or if P. electromorphus uses lower quality habitat as a refuge to avoid P. cinereus. At a site of microsympatry, we repeatedly sampled plots during two seasons, each within a different area of the landscape, and used occupancy and abundance modeling to assess the extent of co‐occurrence and test whether the species use different microhabitat conditions. Plethodon cinereus greatly outnumbered P. electromorphus and occupied a greater proportion of plots, most plots where we detected P. electromorphus we also detected P. cinereus. In contrast to patterns documented in some montane species pairs, in which a high‐elevation habitat specialist excludes a low‐elevation generalist, we found that P. electromorphus primarily used microhabitat conditions favorable for both species, such as north‐facing slopes, yet did not have a negative effect on the abundances of P. cinereus. In the presence of an abundant competitor, microhabitat use of the less abundant species may narrow toward optimal conditions with sufficient resources to facilitate co‐occurrence. [ABSTRACT FROM AUTHOR]

The Chinese giant salamander (Andrias davidianus), listed as an endangered species under "secondary protection" in China, faces significant threats due to ecological deterioration and the expansion of human activity. Extensive field investigations are crucial to ascertain the current status in the wild and to implement effective habitat protection measures to safeguard this species and support its population development. Traditional survey methods often fall short due to the elusive nature of the A. davidianus, presenting challenges that are time-consuming and generally ineffective. To overcome these obstacles, this study developed a real-time monitoring method that uses environmental DNA (eDNA) coupled with recombinase polymerase amplification and lateral flow strip (RPA-LFD). We designed five sets of species-specific primers and probes based on mitochondrial genome sequence alignments of A. davidianus and its close relatives. Our results indicated that four of these primer/probe sets accurately identified A. davidianus, distinguishing it from other tested caudata species using both extracted DNA samples and water samples from a tank housing an individual. This method enables the specific detection of A. davidianus genomic DNA at concentrations as low as 0.1 ng/mL within 50 min, without requiring extensive laboratory equipment. Applied in a field survey across four sites in Huangshan City, Anhui Province, where A. davidianus is known to be distributed, the method successfully detected the species at three of the four sites. The development of these primer/probe sets offers a practical tool for field surveying and monitoring, facilitating efforts in population recovery and resource conservation for A. davidianus. [ABSTRACT FROM AUTHOR]

Simple Summary: Exploring species' potential suitable habitats is crucial for endangered species conservation, in particular under future global climate change conditions. The Wushan salamander (Liua shihi) is an endangered salamander in China, which is a national protected species (level II). Based on the distribution records of L. shihi, the main objective of this study was to predict the distribution of suitable habitats under current and future climate conditions for L. shihi. Our results showed that precipitation, cloud density, vegetation type, and ultraviolet radiation were the main environmental factors affecting the distribution of suitable habitat for L. shihi. At present, the suitable habitats are mainly distributed in the Daba Mountain area. Under the future climate conditions, the area of suitable habitats increased, which mainly occurred in central Guizhou Province. These findings provided important information for the conservation of L. shihi. Climate change has been considered to pose critical threats for wildlife. During the past decade, species distribution models were widely used to assess the effects of climate change on the distribution of species' suitable habitats. Among all the vertebrates, amphibians are most vulnerable to climate change. This is especially true for salamanders, which possess some specific traits such as cutaneous respiration and low vagility. The Wushan salamander (Liua shihi) is a threatened and protected salamander in China, with its wild population decreasing continuously. The main objective of this study was to predict the distribution of suitable habitat for L. shihi using the ENMeval parameter-optimized MaxEnt model under current and future climate conditions. Our results showed that precipitation, cloud density, vegetation type, and ultraviolet radiation were the main environmental factors affecting the distribution of L. shihi. Currently, the suitable habitats for L. shihi are mainly concentrated in the Daba Mountains, including northeastern Chongqing and western Hubei Provinces. Under the future climate conditions, the area of suitable habitats increased, which mainly occurred in central Guizhou Province. This study provided important information for the conservation of L. shihi. Future studies can incorporate more species distribution models to better understand the effects of climate change on the distribution of L. shihi. [ABSTRACT FROM AUTHOR]

Evaluating biomarkers of stress in amphibians is critical to conservation, yet current techniques are often destructive and/or time‐consuming, which limits ease of use. In the present study, we validate the use of dermal swabs in spotted salamanders (Ambystoma maculatum) for biochemical profiling, as well as glutathione (GSH) stress response following pesticide exposure. Thirty‐three purchased spotted salamanders were acclimated to laboratory conditions at Washington College (Chestertown, MD, USA) for 4 weeks. Following acclimation, salamanders were randomly sorted into three groups for an 8‐h pesticide exposure on soil: control with no pesticide, 2,4‐dichlorophenoxyacetic acid (2,4‐D), or chlorpyrifos. Before and after exposure, mucus samples were obtained by gently rubbing a polyester‐tipped swab 50 times across the ventral and dorsal surfaces. Salamanders were humanely euthanized and dissected to remove the brain for acetylcholinesterase and liver for GSH and hepatic metabolome analyses, and a whole‐body tissue homogenate was used for pesticide quantification. Levels of GSH were present in lower quantities on dermal swabs relative to liver tissues for chlorpyrifos, 2,4‐D, and control treatments. However, 2,4‐D exposures demonstrated a large effect size increase for GSH levels in livers (Cohen's d = 0.925, p = 0.036). Other GSH increases were statistically insignificant, and effect sizes were characterized as small for 2,4‐D mucosal swabs (d = 0.36), medium for chlorpyrifos mucosal swabs (d = 0.713), and negligible for chlorpyrifos liver levels (d = 0.012). The metabolomics analyses indicated that the urea cycle, alanine, and glutamate metabolism biological pathways were perturbed by both sets of pesticide exposures. Obtaining mucus samples through dermal swabbing in amphibians is a viable technique for evaluating health in these imperiled taxa. Environ Toxicol Chem 2024;43:1126–1137. © 2024 SETAC [ABSTRACT FROM AUTHOR]

We lack a strong understanding of how organisms with complex life histories respond to climate variation. Many stream-associated species have multistage life histories that are likely to influence the demographic consequences of floods and droughts. However, tracking stage-specific demographic responses requires high-resolution, long-term data that are rare. We used 8 years of capture-recapture data for the headwater stream salamander Gyrinophilus porphyriticus to quantify the effects of flooding and drying magnitude on stage-specific vital rates and population growth. Drying reduced larval recruitment but increased the probability of metamorphosis (i.e., adult recruitment). Flooding reduced adult recruitment but had no effect on larval recruitment. Larval and adult survival declined with flooding but were unaffected by drying. Annual population growth rates (λ) declined with flooding and drying. Lambda also declined over the study period (2012–2021), although mean λ was 1.0 over this period. Our results indicate that G. porphyriticus populations are resilient to hydrologic variation because of compensatory effects on recruitment of larvae versus adults (i.e., reproduction vs. metamorphosis). Complex life cycles may enable this resilience to climate variation by creating opportunities for compensatory demographic responses across stages. However, more frequent and intense hydrologic variation in the latter half of this study contributed to a decline in λ over time, suggesting that increasing environmental variability poses a threat even when demographic compensation occurs. [ABSTRACT FROM AUTHOR]

The fully aquatic Japanese giant salamander (Andrias japonicus) is a member of the Cryptobranchidae, and is currently distributed in western Japan, with other members of this group restricted to China and North America. Their feeding behaviour is characterized by a form of suction feeding that includes asymmetric movements of the jaw and hyobranchial apparatus. Previous studies on the North American species, Cryptobranchus alleganiensis, have suggested that this specialized jaw movement is produced by a flexible quadrate‐articular joint combined with a loosely connected lower jaw symphysis including two small fibrocartilaginous pads. However, little is known about this feeding behaviour in the Asian species, nor have the three‐dimensional asymmetric jaw movements been fully investigated in any member of Cryptobranchidae. In this study, we explore the asymmetric jaw movements in A. japonicus using three methods: (1) dissection of musculoskeletal structures; (2) filming of feeding behaviour to understand in which situations asymmetric feeding is used; (3) analysis of 3D movement of jaws and skull. In the third component, fresh (from frozen) specimens of A. japonicus were manipulated to replicate asymmetric and symmetric jaw movements, with the specimens CT scanned after each step to obtain the 3D morphology of the jaws at different positions. These positions were combined and their Euler angles from resting (closed) jaw position were calculated for asymmetric or symmetric jaw positions. Our filming revealed that asymmetric jaw movements are linked to the position of the prey in relation to the snout, with the jaw closest to the prey opening asymmetrically. Moreover, this action allows the salamander to simultaneously grasp prey in one side of the mouth while ejecting water on the other side, if the first suction attempt fails. The asymmetric jaw movements are performed mainly by rotation of the mandible about its long axis, with very limited lateral jaw movements. During asymmetric and symmetric jaw movements, the posterior ends of the maxilla and quadrate move slightly. The asymmetric jaw movements are permitted by a mobile quadrate‐articular joint formed by wide, round cartilages, and by two small fibrocartilage pads within the jaw symphysis that act as cushions during jaw rotation. Some of these soft tissue structures leave traces on the jaws and skull, allowing feeding mode to be reconstructed in fossil taxa. Understanding cryptobranchid asymmetric jaw movement thus requires a comprehensive assessment of not only the symphysial morphology but also that of other cranial and hyobranchial elements. [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]

In comparison to biodiversity on Earth's surface, subterranean biodiversity has largely remained concealed. The olm (Proteus anguinus) is one of the most enigmatic extant cave inhabitants, and until now little was known regarding its genetic structure and evolutionary history. Olms inhabit subterranean waters throughout the Dinaric Karst of the western Balkans, with a seemingly uniform phenotypic appearance of cave‐specialized traits: an elongate body, snout and limbs, degenerated eyes and loss of pigmentation ("white olm"). Only a single small region in southeastern Slovenia harbours olms with a phenotype typical of surface animals: pigmented skin, eyes, a blunt snout and short limbs ("black olm"). We used a combination of mitochondrial DNA and genome‐wide single nucleotide polymorphism data to investigate the molecular diversity, evolutionary history and biogeography of olms along the Dinaric Karst. We found nine deeply divergent species‐level lineages that separated between 17 and 4 million years ago, while molecular diversity within lineages was low. We detected no signal of recent admixture between lineages and only limited historical gene flow. Biogeographically, the contemporaneous distribution of lineages mostly mirrors hydrologically separated subterranean environments, while the historical separation of olm lineages follows microtectonic and climatic changes in the area. The reconstructed phylogeny suggests at least four independent transitions to the cave phenotype. Two of the species‐level lineages have miniscule ranges and may represent Europe's rarest amphibians. Their rarity and the decline in other lineages call for protection of their subterranean habitats. [ABSTRACT FROM AUTHOR]

The influence of intraspecific trait variation on species interactions makes trait-based approaches critical to understanding eco-evolutionary processes. Because species occupy habitats that are patchily distributed in space, species interactions are influenced not just by the degree of intraspecific trait variation but also the relative proportion of trait variation that occurs within- versus between-patches. Advancement in trait-based ecology hinges on understanding how trait variation is distributed within and between habitat patches across the landscape. We sampled larval spotted salamanders (Ambystoma maculatum) across six spatially discrete ponds to quantify within- and between-pond variation in mass, length, and various metrics associated with their relationship (scaling, body condition, shape). Across all traits, within-pond variation contributed more to total observed morphological variation than between-pond variation. Between-pond variation was not negligible, however, and explained 20–41% of total observed variation in measured traits. Between-pond variation was more pronounced in salamander tail morphology compared to head or body morphology, suggesting that pond-level factors more strongly influence tails than other body parts. We also observed differences in mass-length relationships across ponds, both in terms of scaling slopes and intercepts, though differences in the intercepts were much stronger. Preliminary evidence hinted that newly constructed ponds were a driver of the observed differences in mass-length relationships and morphometrics. General pond-level difference in salamander trait covariation suggest that allometric scaling of morphological traits is context dependent in patchy landscapes. Effects of pond age offer the hypothesis that habitat restoration through pond construction is a driver of variation in trait scaling, which managers may leverage to bolster trait diversity. [ABSTRACT FROM AUTHOR]

For many species, population sizes are unknown despite their importance for conservation. For population size estimation, capture-mark-recapture (CMR) studies are often used, which include the necessity to identify each individual, mostly through individual markings or genetic characters. Invasive marking techniques, however, can negatively affect the individual fitness. Alternatives are low-impact techniques such as the use of photos for individual identification, for species with stable distinctive phenotypic traits. For the individual identification of photos, a variety of different software, with different requirements, is available. The European fire salamander (Salamandra salamandra) is a species in which individuals, both at the larval stage and as adults, have individual specific patterns that allow for individual identification. In this study, we compared the performance of five different software for the use of photographic identification for the European fire salamander: Amphibian & Reptile Wildbook (ARW), AmphIdent, I3S pattern+, ManderMatcher and Wild-ID. While adults can be identified by all five software, European fire salamander larvae can currently only be identified by two of the five (ARW and Wild-ID). We used one dataset of European fire salamander larval pictures taken in the laboratory and tested this dataset in two of the five software (ARW and Wild-ID). We used another dataset of European fire salamander adult pictures taken in the field and tested this using all five software. We compared the requirements of all software on the pictures used and calculated the False Rejection Rate (FRR) and the Recognition Rate (RR). For the larval dataset (421 pictures) we found that the ARW and Wild-ID performed equally well for individual identification (99.6% and 100% Recognition Rate, respectively). For the adult dataset (377 pictures), we found the best False Rejection Rate in ManderMatcher and the highest Recognition Rate in the ARW. Additionally, the ARW is the only program that requires no image pre-processing. In times of amphibian declines, non-invasive photo identification software allowing capture-mark-recapture studies help to gain knowledge on population sizes, distribution, movement and demography of a population and can thus help to support species conservation. [ABSTRACT FROM AUTHOR]

Connectivity is essential for the maintenance of genetic diversity and stability of wildlife populations. Drought and changing precipitation regimes have caused natural aquatic amphibian breeding habitats to disappear or become isolated and have led to the replacement of natural surface water with artificial livestock water tanks. Terrestrial movement is the only means of responding to aquatic threats in arid landscapes and to allow population connectivity. Aridity may present an impenetrable barrier in hydrologically fragmented environments. We used a facultatively paedomorphic and federally endangered salamander to assess the challenges of movement across arid working lands. Sonoran tiger salamanders (Ambystoma mavortium stebbinsi) are endemic to the San Rafael Valley of southeastern Arizona, United States of America, where they depend on livestock water tanks as breeding habitat. The ecology of this species' metamorphs outside of stock tanks is virtually unknown. To assess survival on the landscape during terrestrial movement we used radio‐transmitters to track 78 adult metamorphosed salamanders over 2 years. Sonoran tiger salamanders moved up to 1 km from the tank edge, and average distances moved of over 400 m were higher than most Ambystoma species. However, during the study period, none reached neighboring stock tanks. We found high mortality due to predation and desiccation. Individuals that dispersed to terrestrial habitat in summer survived longer than individuals that dispersed in spring. High mortality suggests terrestrial movement is exceptionally risky and may contribute to isolated subpopulations and elevated levels of inbreeding. Conservation actions that improve and maintain artificial aquatic habitats as well as increase connectivity may improve long‐term management for pond‐breeding amphibians in arid regions. [ABSTRACT FROM AUTHOR]

Neoteny is a developmental strategy wherein an organism reaches sexual maturity without associated adult characteristics. In salamanders, neoteny takes the form of individuals retaining aquatic larval characteristics such as external gills upon maturation. Mole salamanders (Ambystoma) occupy a wide range of habitats and areas across the North American continent, and display examples of non‐neotenic, facultatively neotenic and obligate neotenic species, providing high variation for investigating the factors influencing the evolution of neoteny. Here, we use phylogenetic comparative methods to test existing hypotheses that neoteny is associated with elevational and latitudinal distribution, cave‐associated isolation, and hybridisation‐related polyploidy. We also test if neoteny influences the diversity of habitats a species can occupy, since the restriction to an aquatic life should constrain the availability of different niches. We find that neoteny tends to occur in a narrow latitudinal band between 20–30° North, with particularly narrow latitudinal ranges for obligate compared to facultative neotenic species (16–52° North). We also find that facultatively neotenic species occur at elevations more than twice as high as other species on average, and that species with a higher frequency of neoteny typically have lower habitat diversity. Our results suggest that evolutionary transitions between non‐neotenic and facultative neoteny states occur at relatively high and approximately equal rates. Moreover, we estimate that obligate neoteny cannot evolve directly from non‐neotenic species (and vice versa), such that facultative neoteny acts as an evolutionary 'stepping stone' to and from obligate neoteny. However, our transition rate estimates suggest that obligate neoteny is lost >4‐times faster than it evolves, partly explaining the rarity of obligate species. These results support the hypothesis that low latitudes favour the evolution of neoteny, presumably linked to more stable (aquatic) environments due to reduced seasonality, but once evolved it may constrain the diversity of habitats. [ABSTRACT FROM AUTHOR]

Tonic immobility is an antipredator defence in which the prey animal remains motionless after physical contact with the predator, pretending to be dead. This behaviour has been observed among a variety of taxa but has received only little attention in amphibian larvae. During our field studies with fire salamander larvae, we observed that larvae from different habitats display tonic immobility after handling. In our study site, we find larvae in pond and stream habitats, that differ in several aspects such as their stress response and their risk‐taking behaviour, likely caused by the very different habitat conditions. We measured the time that the tonic immobility behaviour was displayed but found no difference between larvae from the two habitat types. Likewise, we also found no correlation between the size of the larvae and the duration of displaying the behaviour. In conclusion, we found that fire salamander larvae show tonic immobility, but found no evidence that the different habitat conditions influence the tonic immobility behaviour. [ABSTRACT FROM AUTHOR]

Simple Summary: Amphibians are classified into three orders with different morphological characteristics: Anura, Apoda, and Caudata. In this article, the importance of skin for amphibians is discussed as it represents a physical, chemical, immunological, and microbiological barrier to pathogen insult is discussed. Langerhans cells (LCs) are antigen-presenting cells constituting an important component of the immune system in the skin. This study aims to characterize Langerhans cells in the skin of Lithobates catesbeianus (Shaw, 1802), Amphiuma means (Garden, 1821), and Typhlonectes natans (Fischer, 1880) with several antibodies previously used to mark the same cells in other vertebrates. The results showed that the distribution of LCs is very similar in the three amphibian species examined, despite their different habitats. In conclusion, the amphibian dendritic cells are morphologically and immunohistochemically homologous to the LCs of all vertebrates so they can be considered as starting points to better understand the phylogeny of the vertebrate immune system. The amphibian taxon includes three orders that present different morphological characteristics: Anura, Caudata, and Apoda. Their skin has a crucial role: it acts as an immune organ constituting a physical, chemical, immunological, and microbiological barrier to pathogen insult and conducts essential physiological processes. Amphibians have developed specialized features to protect the vulnerable skin barrier, including a glandular network beneath the skin surface that can produce antimicrobial and toxic substances, thus contributing to the defense against pathogens and predators. This study aims to characterize Langerhans cells in the skin of Lithobates catesbeianus (order: Anura; Shaw, 1802), Amphiuma means (order: Caudata; Garden, 1821), and Typhlonectes natans (order: Apoda; Fischer, 1880) with the following antibodies: Langerin/CD207 (c-type lectin), Major Histocompatibility Complex (MHC)II, and Toll-like receptor (TLR)2 (expressed by different types of DCs). Our results showed Langerhans cells positive for Langerin CD/207 in the epidermis of the three species; moreover, some antigen-presenting cells (APCs) in the connective tissue expressed TLR2 and MHCII. The distribution of the Langerhans cells is very similar in the three amphibians examined, despite their different habitats. A greater knowledge of the amphibian immune system could be useful to better understand the phylogeny of vertebrates and to safeguard amphibians from population declines. Furthermore, the similarities between amphibians' and human skin concerning immunological features may be useful in both biology and translational medicine. [ABSTRACT FROM AUTHOR]

Conservation translocations are an important tool for combating species declines and population losses. Species distribution models (SDMs) can facilitate the selection of suitable release sites for translocation programs. However, these models can be sensitive to several modelling decisions.In this study, we explore the impacts of three key modelling decisions on Maxent models developed to inform reintroductions of the long‐toed salamander (Ambystoma macrodactylum) in southwestern Alberta. We specifically test the sensitivity of model predictions to (1) the type of environmental variables used to generate models, (2) whether the background points used to calibrate the models reflects the potential bias in the input locality records and (3) the choice of geographic study extent. We use independent presence‐absence data from an extensive field survey to test the accuracy of models based on different decisions.Both model predictions and performance were sensitive to these modelling decisions. Models developed using local study extents were more accurate than those based on range‐wide extents. Both study extent and type of background points impacted model predictions and performance more than the set of environmental variables included in the models for this species.We further demonstrate the impacts of these decisions on the ranking of potential release sites and present a final set of recommendations that accounts for this uncertainty under both current and future climatic conditions. We specifically identify three sites that are expected to be suitable in both present and future time periods as potential release sites for salamander reintroductions in southwestern Alberta.Synthesis and applications: Our study adds to our understanding of how different modelling decisions impact SDMs and the downstream conclusions from these models while simultaneously demonstrating a rigorous approach for the use of SDMs in conservation translocation planning. [ABSTRACT FROM AUTHOR]

When invasive and endangered native taxa hybridize, the resulting admixture introduces novel conservation challenges. Across a large region of central California, a hybrid swarm consisting of admixed endangered California tiger salamanders (CTS) (Ambystoma californiense) and introduced barred tiger salamanders (BTS) (Ambystoma mavortium) has replaced native populations, threatening the genetic integrity of CTS and the vernal pool systems they inhabit. We employed a large‐scale, genomically informed field experiment to test whether shortening breeding pond hydroperiod would favor native CTS genotypes. We constructed 14 large, seminatural ponds to evaluate the effect of hydroperiod duration on larval survival and mass at metamorphosis. We tracked changes in non‐native allele frequencies with a 5237‐gene exon capture array and employed a combination of custom Bayesian and generalized linear models to quantify the effect of pond duration on salamander fitness. Earlier work on this system showed hybrid superiority under many conditions and suggested that hybrids are favored in human‐modified ponds with artificially long hydroperiods. Consistent with these earlier studies, we found overwhelming evidence for hybrid superiority. Very short hydroperiods substantially reduced the mass (1.1–1.5 fold) and survival probability (10–13 fold) of both native and hybrid larvae, confirming that hydroperiod likely exerts a strong selective pressure in the wild. We identified 86 genes, representing 1.8% of 4723 screened loci, that significantly responded to this hydroperiod‐driven selection. In contrast to earlier work, under our more natural experimental conditions, native CTS survival and size at metamorphosis were always less than hybrids, suggesting that hydroperiod management alone will not shift selection to favor native larval genotypes. However, shortening pond hydroperiod may limit productivity of hybrid ponds, complementing other strategies to remove hybrids while maintaining vernal pool ecosystems. This study confirms and expands on previous work that highlights the importance of hydroperiod management to control invasive aquatic species. [ABSTRACT FROM AUTHOR]

Japanese giant salamander (Andrias japonicus) is one of the largest amphibian species in the world and an iconic species in Japan. However, as its distribution has recently declined across the country, rapid and extensive monitoring of the distribution is urgently needed for its efficient conservation. Here, we used environmental DNA (eDNA) analysis to assess the Japanese giant salamander's distribution in western Japan and, for that purpose, we collected 410 water samples from 12 rivers. We then developed a new eDNA assay for multi-copy nuclear DNA (nuDNA) of the giant salamander and compared the eDNA detectability of the nuDNA marker with that of a previous mitochondrial DNA (mtDNA) marker. Throughout the survey, we detected target eDNA from 162 water samples using either of the markers, which generally corresponded to the known natural distribution of the species. Additionally, the use of the nuDNA marker allowed for higher detection rate of target eDNA than the mtDNA marker. Moreover, the detection rate of target eDNA decreased substantially in water samples with higher conductivity and also partly in those with higher pH, suggesting their negative impacts on the salamander's ecology. Our results demonstrated that eDNA analysis with multi-copy nuDNA marker is highly useful for efficient and sensitive surveillance of Japanese giant salamander's distribution. Our study provided the methodology for efficiently monitoring the Japanese giant salamander's distribution via eDNA analysis and facilitating conservation activities for them. [ABSTRACT FROM AUTHOR]

Ecosystem engineers facilitate beneficiary species by ameliorating physical habitat. The stress‐gradient hypothesis (SGH) predicts the importance of facilitation in communities should increase with physical stress but has rarely been tested in freshwater. Bluehead Chubs (Nocomis leptocephalus) build gravel nests for spawning, which can reduce negative effects of sedimentation for lithophilic species including invertebrates and other taxa. Our goal was to test the SGH using chubs and benthic assemblages as a model system. We surveyed assemblages in chub nests, paired unmodified substrate and reach‐wide samples in 10 Piedmont streams in South Carolina, USA, placed across a gradient of sedimentation. Based on the SGH, we predicted benthic assemblage diversity in chub nests would show no relationship to increasing embeddedness but that diversity in unmodified substrate should decrease with embeddedness. We found that taxa counts, richness and Shannon diversity were higher in chub nests than unmodified substrate but were lower than reach‐wide samples. Canonical correspondence analyses indicated benthic assemblages differed between nests and unmodified substrate, but assemblages in both microhabitats were nested subsets of the more diverse reach‐wide assemblage. Contrary to our hypotheses, diversity in both microhabitats decreased significantly with substrate embeddedness but was consistently higher in nests. While substrate modification by chubs clearly facilitated benthic diversity at the microhabitat scale, it was not sufficient to overcome the worst effects of sedimentation. This study provides mixed evidence for SGH in streams; chub nesting appears to be facilitative at the microhabitat scale but may not have reach‐wide effects on benthic assemblages in this system. [ABSTRACT FROM AUTHOR]

We established a normal embryonic development table for the Anji salamander Hynobius amjiensis , a critically endangered tailed amphibian of the family Hynobiidae with a very limited distribution in East China, following the standards set by the early developmental table of vertebrates. Put together 32 embryonic stages for the Anji salamander was defined. The total embryonic period from oviposition to hatching is approximately 30 days at 9 °C. Stages 1–16 represent early development from cleavage to neurulation. Stages 17–32 represent organogenesis documenting later developmental events such as tail, gill, and limb formation, and hatching (Stage 32). We provided a detailed description of the external morphology and color changes of the head, trunk, limbs, tail, external gills, and balancers at various stages from egg-laying to hatching. We also described several cases of abnormal embryonic development. The establishment of the embryonic development table in H. amjiensis contributes to better understanding of the ontogeny in tailed amphibians, distinguishing closely related species, and identifying abnormal embryonic amphibians. [Display omitted] • We established a normal embryonic development table for the Anji salamander. • We expanded the organogenesis period into 16 stages. • We described several cases of abnormal embryonic development. [ABSTRACT FROM AUTHOR]

Introduction: Given the role of microbiomes in promoting host health and homeostasis, understanding the factors shaping skin microbial communities in wild vertebrates has become increasingly important in conservation. This goal is even more pressing for amphibians, for which the skin has multiple critical functions, and pathogens currently decimating populations are linked to significant changes in skin microbiomes. However, because microbiomes are also shaped by environmental and ecological influences, as well as by host phylogeny, it is important to quantify these contributions to microbiome structure in the presence of infection. Methods: To understand the joint influence of these diverse factors shaping microbiomes, we used 16S rRNA sequencing to characterize the skin microbial communities of six salamander species (families Plethodontidae and Salamandridae) found in Oklahoma and contrasted the effects of infection status, phylogeny, host ecology, and host environment (i.e., climate) on skin microbiomes. Results: Differences at the level of host family were the main factor influencing microbiome diversity; however, we did not detect a substantial phylogenetic signal. Instead, host ecology and environment were more important in driving microbiome differences among species and genera. Salamanders that tested positive for the skin fungal parasite Batrachochytrium dendrobatidis (Bd) also had slightly less diverse microbiomes than Bd-free animals, but no such differences were associated with the systemic pathogen ranavirus (RV). Discussion: Together, these results indicate a nuanced relationship between the number and type of microbes present on salamander skin and the factors influencing them. By developing a baseline assessment of the microbiome diversity and richness present on the skin of these focal species, this work also provides a foundation for monitoring and evaluating changes in skin microbiomes as populations continue to experience stressors and diseases. [ABSTRACT FROM AUTHOR]

Survival rates are known to vary over the course of an individual's lifetime and among individuals within a population. Quantifying the natural variability in survival rates is crucial when scaling up to infer the dynamics of populations. Using ten years of mark-recapture data from two adjacent wetlands on the Florida Panhandle, we investigated individual and temporal variability in survival rates of Reticulated Flatwoods Salamanders (Ambystoma bishopi). Our objectives were to 1) provide the first estimates of survival for the species, 2) evaluate the relationship between body size and mortality risk, 3) quantify the degree of variability in survival rates across the study period, and 4) discern whether variability in survival or detection correlates with environmental conditions. To address these objectives, we constructed a modified Cormack-Jolly-Seber model that includes body size and year as covariates. Mean annual survival was estimated to be 0.72 and was strongly correlated with body size; survival rates of the smallest individuals in the study were 0.5 and those of the largest individuals were 0.85. Survival also varied considerably across years, but it did not correlate with temperature extremes or rainfall. Therefore, a key priority for future research should be to identify the ecological correlates of mortality risk in A. bishopi. Our results can be integrated into demographic projections for Reticulated Flatwoods Salamanders and will help managers to discern population viability, evaluate alternative management strategies (e.g., habitat restoration), or buffer the impacts of climate change. More broadly, our work highlights the need for more long-term studies that will garner accurate estimates of vital rates to aid ongoing recovery efforts for endangered and at-risk species. [ABSTRACT FROM AUTHOR]

Worldwide, amphibians are experiencing high rates of decline. Large-scale, long-term studies of amphibians are crucial for uncovering potential causes of the declines; however, such long-term studies remain rare, particularly for salamanders. In this study, we monitored populations of Spotted Salamanders (Ambystoma maculatum) in 90 Connecticut, USA, ponds. Populations were divided between an inland, undeveloped landscape monitored for up to 23 yr and a coastal, developed landscape monitored for up to 9 yr. We measured the density of egg masses (number of egg masses per unit of search effort) each year at each pond for a total of 1392 pond-years of sampling effort and asked how egg mass densities and breeding probability relate to local environmental and climatic conditions. In the undeveloped landscape, average egg mass densities have declined by ∼30% over the course of 2 decades. The presence of salamander breeding activity was positively associated with spring pond depth, and pond depth itself has declined by ∼20% during the survey period. We also found that egg mass density was related to road proximity and developed land cover: egg mass densities tended to be higher in ponds near roads and in ponds with less development within a 200-m buffer. In the developed landscape, egg mass densities showed a nonsignificant declining trend from 2014 to 2022 and salamander breeding activity was positively associated with higher canopy cover and larger pond surface area. Our findings suggest that even in a protected landscape with increasing forest cover, spotted salamander egg mass densities are declining at a rate of 1.6%/yr. Decreasing pond depths are likely linked to decreased water yield as forests grow, which could affect pond hydroperiods (aquatic larval habitat) as well as forest soil moisture levels (adult habitat). Overall, increasing development may continue to negatively affect habitat of Spotted Salamanders and it is possible that forest maturation also has a negative influence on salamanders—an effect not documented previously. [ABSTRACT FROM AUTHOR]

Hatching plasticity allows animals to initiate hatching in response to environmental cues including predation, flooding, and hypoxia. In species with terrestrial eggs but aquatic larvae, hatching plasticity often manifests as extended development of embryos when water is not available. Although these effects are taxonomically widespread, little attention has focused on differences in plasticity across closely related species with terrestrial and aquatic embryos. We propose that the terrestrial embryonic environment favors slower and prolonged development and, consequently, that we should see differences in development between closely related species that differ in where they lay their eggs. We test this hypothesis by comparing embryonic development between two mole salamanders, Ambystoma opacum and A. annulatum. Most Ambystoma lay eggs submerged in ponds but A. opacum lays its eggs on land, where hatching is triggered when eggs are submerged by rising pond levels. Embryos of both species were reared under common laboratory conditions simulating both aquatic and terrestrial nest sites. Consistent with our hypothesis, we found that A. opacum embryos exhibited slower development and took longer to hatch than A. annulatum embryos in both rearing environments. Furthermore, we observed in A. opacum a plasticity in hatching stage that was absent in A. annulatum. Our results indicate that the terrestrial‐laying A. opacum has evolved slower and prolonged development relative to its aquatic‐laying congener and suggest that embryonic survival in the unpredictable terrestrial environment may be facilitated by developmental plasticity. [ABSTRACT FROM AUTHOR]

The Jilin clawed salamander (Onychodactylus zhangyapingi) is an endemic, endangered, and level‐two protected amphibian species of China. In the context of serious threats to amphibians worldwide, conservation studies of this endangered species are urgently needed. In this study, mitogenomic conservation genetics and species distribution modeling analyses were performed for O. zhangyapingi. Sixty‐three samples were collected from nine different locations, and the complete mitochondrial genome was sequenced. Population genetic analyses revealed that O. zhangyapingi exhibits only one genetic structure with extremely low nucleotide diversity. Late Pleistocene climate cooling may have led to a reduction in effective population size and extremely low mitogenomic nucleotide diversity in this salamander, and the subsequent temperature increase (~20 kya to present) provided the opportunity for rapid population growth. The continuous highly suitable region for O. zhangyapingi is only approximately 3000 km2 on the southeastern boundary of Jilin Province, China. Fortunately, there are three large forested national nature reserves within the distribution of O. zhangyapingi that can effectively protect endangered species. Our findings suggest that O. zhangyapingi is a vulnerable species with a narrow distribution and extremely low genetic diversity, and we should pay more attention to the conservation management of this species. [ABSTRACT FROM AUTHOR]

The largest cells are orders of magnitude bigger than the smallest cells. Organelle content scales to maintain cell function, with different organelles increasing in volume, length, or number as cells increase in size. Scaling may also reflect functional demands placed on organelles by increased cell size. Amphibians exhibit exceptional diversity in cell size. Using transmission electron microscopy, we analyzed 3 species whose enterocyte cell volumes range from 228 to 10,593 μm3. We show that nuclear volume increases by an increase in radius while mitochondrial volume increases by an increase in total network length; the endoplasmic reticulum and Golgi apparatus, with their complex shapes, are intermediate. Notably, all 4 organelle types increase in total volume proportional to cell volume, despite variation in functional (i.e. metabolic, transport) demands. This pattern suggests that organellar building blocks are incorporated into more or larger organelles following the same rules across species that vary ~50-fold in cell sizes, consistent with a "limited precursor" model for organellar scaling that, in turn, assumes equivalent cytoplasmic concentrations of organellar building block proteins. Taken together, our results lead us to hypothesize that salamanders have evolved increased biosynthetic capacity to maintain functional protein concentrations despite huge cell volumes. [ABSTRACT FROM AUTHOR]

Simple Summary: Biodiversity conservation under global climate change is a global challenge. Many wildlife species are altering their distributions to adapt to the changes in their living environments caused by climate change. Amphibians are the most vulnerable group among vertebrates in the context of global climate change, and salamanders are one of the most vulnerable groups among amphibians. The primary threat to salamanders is habitat loss. There have been multiple studies on the potential distribution prediction of umbrella species (umbrella species are those species whose conservation is expected to provide protection for a wide range of co-occurring species due to their extensive habitat requirements), such as the Chinese giant salamander (Andrias davidianus). However, research on rare small salamanders is urgently needed for their conservation under climate change conditions. This study employed an optimized MaxEnt model to predict and analyze the potential distribution and trends of three rare salamanders from Chongqing, China, based on data collected from field surveys, museum collections, and the existing literature. This study assesses the impact of various environmental factors in the context of climate change on three salamanders species with different habitat preferences in Chongqing. It offers implications for the conservation of these salamanders. The Wushan Salamander (Liua shihi), Jinfo Salamander (Pseudohynobius jinfo), and Wenxian Knobby Salamander (Tylototriton wenxianensis) are rare national Class II protected wild animals in China. We performed MaxEnt modeling to predict and analyze the potential distribution and trends of these species in Chongqing under current and future climate conditions. Species distribution data were primarily obtained from field surveys, supplemented by museum collections and the existing literature. These efforts yielded 636 records, including 43 for P. jinfo, 23 for T. wenxianensis, and 570 for L. shihi. Duplicate records within the same 100 m × 100 m grid cell were removed using ENMTools, resulting in 10, 12, and 58 valid distribution points for P. jinfo, T. wenxianensis, and L. shihi, respectively. The optimization of feature class parameters (FC) and the regularization multiplier (RM) were applied using R package "ENMeval 2.0" to establish the optimal model with MaxEnt. The refined models were applied to simulate the suitable distribution areas for the three species. The results indicate that the current suitable habitat area for L. shihi accounted for 9.72% of the whole region of the Chongqing municipality. It is projected that, by 2050, the proportion of suitable habitat will increase to 12.54% but will decrease to 11.98% by 2070 and further decline to 8.80% by 2090. The current suitable habitat area for P. jinfo accounted for 1.08% of the whole region of the Chongqing municipality, which is expected to decrease to 0.31%% by 2050, 0.20% by 2070, and 0.07% by 2090. The current suitable habitat area for T. wenxianensis accounted for 0.81% of the whole region of the Chongqing municipality, which is anticipated to decrease to 0.37% by 2050, 0.21% by 2070, and 0.06% by 2090. Human disturbance, climate variables, and habitat characteristics are the primary factors influencing the distribution of three salamander species in Chongqing. The proximity to roads significantly impacts L. shihi, while climate conditions mainly affect P. jinfo, and the distance to water sources is crucial for T. wenxianensis. The following suggestions were made based on key variables identified for each species: (1) For L. shihi, it is imperative to minimize human disturbances and preserve areas without roads and the existing vegetation within nature reserves to ensure their continued existence. (2) For P. jinfo, the conservation of high-altitude habitats is of utmost importance, along with the reduction in disturbances caused by roads to maintain the species' ecological niche. (3) For T. wenxianensis, the protection of aquatic habitats is crucial. Additionally, efforts to mitigate the impacts of road construction and enhance public awareness are essential for the preservation of this species and the connectivity of its habitats. [ABSTRACT FROM AUTHOR]

Actuarial senescence (called 'senescence' hereafter) often shows broad variation at the intraspecific level. Phenotypic plasticity likely plays a central role in among‐individual heterogeneity in senescence rate (i.e. the rate of increase in mortality with age), although our knowledge on this subject is still very fragmentary. Polyphenism—the unique sub‐type of phenotypic plasticity where several discrete phenotypes are produced by the same genotype—may provide excellent study systems to investigate if and how plasticity affects the rate of senescence in nature.In this study, we investigated whether facultative paedomorphosis influences the rate of senescence in a salamander, Ambystoma mavortium nebulosum. Facultative paedomorphosis, a unique form of polyphenism found in dozens of urodele species worldwide, leads to the production of two discrete, environmentally induced phenotypes: metamorphic and paedomorphic individuals. We leveraged an extensive set of capture–recapture data (8948 individuals, 24 years of monitoring) that were analysed using multistate capture–recapture models and Bayesian age‐dependent survival models.Multistate models revealed that paedomorphosis was the most common developmental pathway used by salamanders in our study system. Bayesian age‐dependent survival models then showed that paedomorphs have accelerated senescence in both sexes and shorter adult lifespan (in females only) compared to metamorphs. In paedomorphs, senescence rate and adult lifespan also varied among ponds and individuals. Females with good body condition and high lifetime reproductive success had slower senescence and longer lifespan. Late‐breeding females also lived longer but showed a senescence rate similar to that of early‐breeding females. Moreover, males with good condition had longer lifespan than males with poor body condition, although they had similar senescence rates. In addition, late‐breeding males lived longer but, unexpectedly, had higher senescence than early‐breeding males.Overall, our work provides one of the few empirical cases suggesting that environmentally cued polyphenism could affect the senescence of a vertebrate in nature, thus providing insights on the ecological and evolutionary consequences of developmental plasticity on ageing. [ABSTRACT FROM AUTHOR]

Modularity describes the degree to which the components of complex phenotypes vary semi-autonomously due to developmental, genetic and functional correlations. This is a key feature underlying the potential for evolvability, as it can allow individual components to respond to different selective pressures semi-independently. The vertebrate lower jaw has become a model anatomical system for understanding modularity, but to date most of this work has focused on the mandible of mammals and other amniotes. In contrast, modularity in the mandible of lissamphibians has been less well studied. Here, we used geometric morphometrics to quantify the static (intraspecific) modularity patterns in Xenopus laevis and Salamandra salamandra gigliolii. We tested developmental and functional hypotheses of modularity and demonstrate that both species exhibit significant modularity. Functional modularity was supported in both Xenopus and Salamandra. Allometry has a small yet significant impact on lower jaw shape in both taxa and sex has a significant effect on shape in Xenopus. The high lower jaw modularity in both species observed here, combined with the well-established modularity of the amphibian cranium, suggests that modularity is a ubiquitous feature of the tetrapod head. [ABSTRACT FROM AUTHOR]

Natural plants of Camellia (Theaceae) in Thailand are taxonomically revised with a key, a distribution map, descriptions, specimens examined, and figures of living plants and/or dry specimens. Nine taxa comprising seven species and two varieties are recognized, including C. caudata, C. connata, C. furfuracea, C. kissi, C. kissi var. confusa, C. laotica, C. sinensis var. assamica, C. suddeeana, and C. taliensis. Camellia caudata and C. laotica are new records to Thailand, and C. connata and C. suddeeana are endemic to the country. Formerly recorded C. pleurocarpa and C. tenii are excluded from Thai flora because of misidentification, and C. oleifera and C. sinensis are merely cultivated in the country. Morphological descriptions of C. connata and C. laotica are improved based on additional collections examined. [ABSTRACT FROM AUTHOR]

Color polymorphic species provide an excellent opportunity to investigate the ecology and evolution of intraspecific niche differences. The red‐backed salamander, Plethodon cinereus, is a fully terrestrial lungless salamander with two common color forms, striped and unstriped. Previous research suggests the morphs may be differentially adapted to surface and subsurface microhabitats, with the unstriped morph being more fossorial. This hypothesis predicts that the unstriped morph should be more sensitive to the risks of surface activity (e.g., thermal stress, dehydration, predation), and therefore be more selective than striped morphs when choosing soil surface microhabitats. To test this hypothesis, we experimentally manipulated leaf litter mass in small forest patches (~0.45 m2). Leaf litter addition reduced soil temperatures, buffered against changes in air temperature, and likely provided physical protection from predators. Over 3 years, we found that unstriped adults responded positively to leaf litter addition, but striped adults did not. In addition, unstriped morphs spent significantly more time in protective refuges (opaque, moistened tubes) than striped morphs in laboratory assays. Taken together, the field and laboratory results support the hypothesis that the unstriped morph is more sensitive to the risks of surface activity, and therefore is more likely to be fossorial. This difference in microhabitat use, combined with spatiotemporal variation in leaf litter accumulation on the forest floor, may play an important role in the maintenance of the polymorphism. [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]

The potential emergence of zoonotic diseases has raised significant concerns, particularly in light of the recent pandemic, emphasizing the urgent need for scientific preparedness. The bioprospection and characterization of new molecules are strategically relevant to the research and development of innovative drugs for viral and bacterial treatment and disease management. Amphibian species possess a diverse array of compounds, including antimicrobial peptides. This study identified the first bioactive peptide from Salamandra salamandra in a transcriptome analysis. The synthetic peptide sequence, which belongs to the defensin family, was characterized through MALDI TOF/TOF mass spectrometry. Molecular docking assays hypothesized the interaction between the identified peptide and the active binding site of the spike WT RBD/hACE2 complex. Although additional studies are required, the preliminary evaluation of the antiviral potential of synthetic SS-I was conducted through an in vitro cell-based SARS-CoV-2 infection assay. Additionally, the cytotoxic and hemolytic effects of the synthesized peptide were assessed. These preliminary findings highlighted the potential of SS-I as a chemical scaffold for drug development against COVID-19, hindering viral infection. The peptide demonstrated hemolytic activity while not exhibiting cytotoxicity at the antiviral concentration. [ABSTRACT FROM AUTHOR]