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Characterizing the population density of species is a central interest in ecology. Eastern North America is the global hotspot for biodiversity of plethodontid salamanders, an inconspicuous component of terrestrial vertebrate communities, and among the most widespread is the eastern red-backed salamander, Plethodon cinereus. Previous work suggests population densities are high with significant geographic variation, but comparisons among locations are challenged by lack of standardization of methods and failure to accommodate imperfect detection. We present results from a large-scale research network that accounts for detection uncertainty using systematic survey protocols and robust statistical models. We analysed mark-recapture data from 18 study areas across much of the species range. Estimated salamander densities ranged from 1950 to 34 300 salamanders ha-1, with a median of 9965 salamanders ha-1. We compared these results to previous estimates for P. cinereus and other abundant terrestrial vertebrates. We demonstrate that overall the biomass of P. cinereus, a secondary consumer, is of similar or greater magnitude to widespread primary consumers such as white-tailed deer (Odocoileus virginianus) and Peromyscus mice, and two to three orders of magnitude greater than common secondary consumer species. Our results add empirical evidence that P. cinereus, and amphibians in general, are an outsized component of terrestrial vertebrate communities in temperate ecosystems.

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Trait functionality can act as a constraint on morphological development. Traits that become vestigialized can exhibit unstable developmental patterns such as fluctuating asymmetry (FA) and variation in populations. We use clearing and staining along with morphometric analyzes to compare FA and allometry of limbs in Western lesser sirens (Siren nettingi) to Ouachita dusky salamanders (Desmognathus brimleyorum). Our results describe new carpal phenotypes and carpal asymmetry in our sample of S. nettingi. However, we found no significant evidence of limb length asymmetry in S. nettingi. The degree of relative limb asymmetry correlates inversely with body size in both of our samples. This work provides strong evidence of increased mesopodal variation within a population of S. nettingi. Our work provides a basis for further study of a broader range of morphological traits across salamanders.

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Skin microbiomes in amphibians are complex systems that can be influenced by biotic and abiotic factors. In this study, we examined the effect of host species and environmental conditions on the skin bacterial and fungal microbiota of four obligate paedomorphic salamander species, commonly known as axolotls (Ambystoma andersoni, A. dumerilii, A. mexicanum, and A. taylori), all of them endemic to the Trans-Mexican Volcanic Belt. We found that despite their permanent aquatic lifestyle, these species present a host-specific skin microbiota that is distinct from aquatic communities. We identified skin-associated taxa that were unique to each host species and that differentiated axolotl species based on alpha and beta diversity metrics. Moreover, we identified a set of microbial taxa that were shared across hosts with high relative abundances across skin samples. Specifically, bacterial communities were dominated by Burkholderiales and Pseudomonadales bacterial orders and Capnodiales and Pleosporales fungal orders. Host species and environmental variables collectively explained more microbial composition variation in bacteria (R2 = 0.46) in comparison to fungi (R2 = 0.2). Our results contribute to a better understanding of the factors shaping the diversity and composition of skin microbial communities in Ambystoma. Additional studies are needed to disentangle the effects of specific host associated and environmental factors that could influence the skin microbiome of these endangered species.

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Genome size variation in eukaryotes has myriad effects on organismal biology from the genomic to whole-organism level. Large genome size may be associated with lower selection efficiency because lower effective population sizes allow fixation of deleterious mutations via genetic drift, increasing genome size and decreasing selection efficiency. Because of a hypothesized negative relationship between genome size and recombination rate per base pair, increased genome size could also increase the effect of linked selection in the genome, decreasing the efficiency with which natural selection can fix or remove mutations. We used a transcriptomic dataset of 15 and a subset of six Neotropical salamander species ranging in genome size from 12 to 87 pg to study the relationship between genome size and efficiency of selection. We estimated dN/dS of salamanders with small and large genomes and tested for relaxation of selection in the larger genomes. Contrary to our expectations, we did not find a significant relationship between genome size and selection efficiency or strong evidence for higher dN/dS values in species with larger genomes for either species set. We also found little evidence for relaxation of selection in species with larger genomes. A positive correlation between genome size and range size (a proxy of population size) in this group disagrees with predictions of stronger drift in species with larger genomes. Our results highlight the complex interactions between the many forces shaping genomic variation in organisms with genomic gigantism.

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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.

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Two ranavirus isolates were recovered from anuran and salamander samples collected during an amphibian mass mortality event in North-Central Florida in 2021. Phylogenetic analyses of the full genomes confirmed that the two isolates were nearly identical and strains of the species Frog virus 3.

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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.

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There is a recent growing interest in the study of evolutionary and behavioral ecology of amphibians. Among salamanders, Plethodontidae is the most speciose family, with more than 500 species, while in Europe, there are only 8 species, all belonging to the genus Speleomantes. European plethodontids recently received increasing attention with regard to the study of their natural history, ecology and behavior; however, the lack of standardized data, especially for the latter, hampers comparative analysis with the species from the New World. We here synthetized the recent advances in Speleomantes behavioral ecology, considering as a starting point the comprehensive monography of Lanza and colleagues published in 2006. We identified the behavioral categories that were investigated the most, but we also highlighted knowledge gaps and provided directions for future studies. By reviewing the scientific literature published within the period 2006-2022, we observed a significant increase in the number of published articles on Speleomantes behavior, overall obtaining 36 articles. Behavioral studies on Speleomantes focused mainly on trophic behavior (42%), and on intraspecific behavior (33%), while studies on pheromonal communication and interspecific behavioral interactions were lacking. In addition, most of the studies were observational (83%), while the experimental method was rarely used. After providing a synthesis of the current knowledge, we suggest some relevant topics that need to be considered in future research on the behavioral ecology of European plethodontids, highlighting the importance of a more integrative approach in which both field observations and planned experiments are used.

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The vomer is an important tooth-bearing cranial bone in the lungless salamanders (Caudata: Plethodontidae) that serves different functional roles in aquatic versus terrestrial feeding. Vomerine tooth rows that run parallel with the maxillary teeth are thought to help grasp prey while expelling water from the mouth, while posterior extensions of the tooth row may help terrestrial taxa bring prey down the throat. We hypothesize that these two general morphological types will correlate with the habitat (aquatic vs. terrestrial) of adult salamanders. Alternatively, variation in form may be due to taxonomic effects, such that closely related species will have similar vomer morphology regardless of adult habitat. To test this hypothesis, we examined vomer shape on a set of species of the morphologically diverse tribe Spelerpini, in which two of the five genera (Eurycea and Gyrinophilus) include both aquatic and terrestrial species. Data were collected using micro computed tomography (micro-CT) scans from specimens from the Field Museum of Natural History and the Illinois Natural History Survey; additional data was obtained from public online repositories including Morphosource.org. Two-dimensional geometric morphometric analyses were performed to capture shape variation of both the vomer and the vomerine tooth row. We found clear separation between aquatic and terrestrial taxa, with most of the variation due to differences in the vomerine tooth row. Differences ascribed to habitat use likely correspond to feeding behavior, and the functional role of the vomer in prey processing warrants further investigation in this species-rich salamander family.

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Exploitative competition and interference competition differ in the way access to resources is modulated by a competitor. Exploitative competition implies resource depletion and usually produces spatial segregation, while interference competition is independent from resource availability and can result in temporal niche partitioning. Our aim is to infer the presence of spatial or temporal niche partitioning on a two-species system of terrestrial salamanders in Northern Italy: Speleomantes strinatii and Salamandrina perspicillata. We conducted 3 repeated surveys on 26 plots in spring 2018, on a sampling site where both species are present. We modelled count data with N-mixture models accounting for directional interactions on both abundance and detection process. In this way we were able to disentangle the effect of competitive interaction on the spatial scale, i.e., local abundance, and from the temporal scale, i.e., surface activity. We found strong evidence supporting the presence of temporal niche partitioning, consistent with interference competition. At the same time, no evidence of spatial segregation has been observed.

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Fitness trade-offs are a foundation of ecological and evolutionary theory because trade-offs can explain life history variation, phenotypic plasticity, and the existence of polyphenisms. Using a 32-year mark-recapture dataset on lifetime fitness for 1093 adult Arizona tiger salamanders (Ambystoma mavortium nebulosum) from a high elevation, polyphenic population, we evaluated the extent to which two life history morphs (aquatic paedomorphs vs. terrestrial metamorphs) exhibited fitness trade-offs in breeding and body condition with respect to environmental variation (e.g. climate) and internal state-based variables (e.g. age). Both morphs displayed a similar response to higher probabilities of breeding during years of high spring precipitation (i.e. not indicative of a morph-specific fitness trade-off). There were likely no climate-induced fitness trade-offs on breeding state for the two life history morphs because precipitation and water availability are vital to amphibian reproduction. Body condition displayed a contrasting response for the two morphs that was indicative of a climate-induced fitness trade-off. While metamorphs exhibited a positive relationship with summer snowpack conditions, paedomorphs were unaffected. Fitness trade-offs from summer snowpack are likely due to extended hydroperiods in temporary ponds, where metamorphs gain a fitness advantage during the summer growing season by exploiting resources that are unavailable to paeodomorphs. However, paedomorphs appear to have the overwintering fitness advantage because they consistently had higher body condition than metamorphs at the start of the summer growing season. Our results reveal that climate and habitat type (metamorphs as predominately terrestrial, paedomorphs as fully aquatic) interact to confer different advantages for each morph. These results advance our current understanding of fitness trade-offs in this well-studied polyphenic amphibian by integrating climate-based mechanisms. Our conclusions prompt future studies to explore how climatic variation can maintain polyphenisms and promote life history diversity, as well as the implications of climate change for polyphenisms.

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A new salamander species of the genus Bolitoglossa is here described from the cloud forests of the western slopes of the Cordillera Oriental of Colombia, in the Cundinamarca department. The most salient characters of this new species are its numerous maxillary and vomerine teeth, its moderate webbing on hands and feet, its short and robust tail, and its chromatic variation. Based on molecular analyses this new species is assigned to the adspersa species group and its status established as the sister species of B.adspersa, with which it was previously confused. Lastly, the distribution, natural history, and conservation status of the new species are discussed.

ResumenDescribimos una nueva especie de salamandra del género Bolitoglossa proveniente de los bosques nublados de la vertiente occidental de la Cordillera Oriental de Colombia, en el departamento de Cundinamarca. Los caracteres más sobresalientes de esta nueva especie son sus numerosos dientes maxilares y vomerinos, su palmeadura moderada en pies y manos, su cola corta pero robusta, y su variación cromática. Basados en análisis moleculares asignamos esta nueva especie al grupo de especies adspersa y establecemos su estatus como especie hermana de B.adspersa, con la cual era previamente confundida. Finalmente, discutimos algunos aspectos de su distribución, historia natural y su estado de conservación.

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Amphibians have been consumed as an alternative protein source all around the world due to their delicacy. The skin of edible amphibians, particularly frogs and giant salamanders, always goes to waste without further utilization. However, these wastes can be utilized to extract protein and bioactive peptides (BPs). Various BPs have been extracted and reported for numerous biological activities such as antioxidant, antimicrobial, anticancer, antidiabetic, etc. The main BPs identified were brevinins, bombesins, dermaseptins, esculentins, magainin, temporins, tigerinins, and salamandrins. This review provides a comprehensive discussion on various BPs isolated and identified from different amphibian skins or skin secretion and their biological activities. The general nutritional composition and production statues of amphibians were described. Additionally, multiple constraints against the utilization of amphibian skin and secretions are reported. Finally, the prospective applications of BPs in food and biomedical industries are presented such as multifunctional food additives and/or supplements as well as drug delivery agents.

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This review summarizes the role of environmental factors on amphibian microbiotas at the organismal, population, community, ecosystem, and biosphere levels. At the organismal-level, tissue source, disease status, and experimental manipulations were the strongest predictors of variation in amphibian microbiotas. At the population-level, habitat quality, disease status, and ancestry were commonly documented as drivers of microbiota turnover. At the community-level, studies focused on how species' niche influence microbiota structure and function. At the ecosystem-level, abiotic and biotic reservoirs were important contributors to microbiota structure. At the biosphere-level, databases, sample banks, and seminatural experiments were commonly used to describe microbiota assembly mechanisms among temperate and tropical amphibians. Collectively, our review demonstrates that environmental factors can influence microbiotas through diverse mechanisms at all biological scales. Importantly, while environmental mechanisms occurring at each of the different scales can interact to shape microbiotas, the past 10 years of research have mostly been characterized by targeted approaches at individual scales. Looking forward, efforts considering how environmental factors at multiple organizational levels interact to shape microbiota diversity and function are paramount. Generating opportunities for meaningful cross-disciplinary interactions and supporting infrastructure for research that spans biological scales are imperative to addressing this gap.

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Three-dimensional (3D) bioprinting is driving significant innovations in biomedicine over recent years. Under certain scenarios such as in intraoperative bioprinting, the bioinks used should exhibit not only cyto/biocompatibility but also adhesiveness in wet conditions. Herein, an adhesive bioink composed of gelatin methacryloyl, gelatin, methacrylated hyaluronic acid, and skin secretion of Andrias davidianus is designed. The bioink exhibits favorable cohesion to allow faithful extrusion bioprinting in wet conditions, while simultaneously showing good adhesion to a variety of surfaces of different chemical properties, possibly achieved through the diverse bonds presented in the bioink formulation. As such, this bioink is able to fabricate sophisticated planar and volumetric constructs using extrusion bioprinting, where the dexterity is further enhanced using ergonomic handheld bioprinters to realize in situ bioprinting. In vitro experiments reveal that cells maintain high viability; further in vivo studies demonstrate good integration and immediate injury sealing. The characteristics of the bioink indicate its potential widespread utility in extrusion bioprinting and will likely broaden the applications of bioprinting toward situations such as in situ dressing and minimally invasive tissue regeneration.

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For 70 years from the very beginning of developmental biology, the salamander embryo was the pre-eminent model for these studies. Here I review the major discoveries that were made using salamander embryos including regionalization of the mesoderm; patterning of the neural plate; limb development, with the pinnacle being Spemann's Nobel Prize for the discovery of the organizer; and the phenomenon of induction. Salamanders have also been the major organism for elucidating discoveries in organ regeneration, and these are described here too beginning with Spallanzani's experiments in 1768. These include the neurotrophic hypothesis of regeneration, studies of aneurogenic limbs, the concept of dedifferentiation and transdifferentiation, and advances in understanding pattern formation via molecules located on the cell surface. Also described is the prodigious power of brain and spinal cord regeneration and discoveries from lens regeneration, all of which reveal how important salamanders have been as research models.

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The disjunct geographical range of many lineages of caudates points to a complex evolutionary and biogeographic history that cannot be disentangled by only considering the present-day distribution of salamander biodiversity. Here, we provide a critical reappraisal of the published fossil record of caudates from the Palearctic and quantitatively evaluate the quality of the group's fossil record. Stem-Urodela and Karauridae were widespread in the Palearctic in the Middle Jurassic, suggesting an earlier, unsampled diversification for this group. Cryptobranchidae reached Europe no later than the Oligocene, but this clade was subsequently extirpated from this continent, as well as from western and central Asia. The relatively recent appearance of hynobiids in the fossil record (Early Miocene) is most likely an artefact of a taphonomic bias against the preservation of high-mountain, stream-type environments which early members likely inhabited. Salamandroids first appear in Europe, expanding into Asia by the Miocene. The apparently enigmatic and disjunct distribution of extant caudate lineages is therefore explained by a wider past geographical range, as testified by the fossil record, which was fragmented during the late Cenozoic by a combination of tectonic (i.e. the uplift of the Tibetan Plateau) and climatic drivers, resulting in regional extirpations.

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In numerous clades, divergent sister species have largely non-overlapping geographic ranges. This pattern presumably arises because species diverged in allopatry or parapatry, prior to a subsequent contact. Here, we provide population-genomic evidence for the opposite scenario: previously sympatric ecotypes that have spatially separated into divergent monomorphic populations over large geographic scales (reverse sympatric scenario). We analyzed a North American salamander (Plethodon cinereus) with two color morphs that are broadly sympatric: striped (redback) and unstriped (leadback). Sympatric morphs can show considerable divergence in other traits, and many Plethodon species are fixed for a single morph. Long Island (New York) is unusual in having many pure redback and leadback populations that are spatially separated, with pure redback populations in the west and pure leadbacks in the east. Previous work showed that these pure-morph populations were genetically, morphologically, and ecologically divergent. Here, we performed a coalescent-based analysis of new data from 88,696 single-nucleotide polymorphisms to address the origins of these populations. This analysis strongly supports the monophyly of Long Island populations and their subsequent divergence into pure redback and pure leadback populations. Taken together, these results suggest that the formerly sympatric mainland morphs separated into parapatric populations on Long Island, reversing the conventional speciation scenario.

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AbstractAvoiding inbreeding is considered a key driver of dispersal evolution, and dispersal distances should be especially important in mediating inbreeding risk because the likelihood of mating with relatives decreases with dispersal distance. However, a lack of direct data on dispersal distances has limited empirical tests of this prediction, particularly in the context of the multiple selective forces that can influence dispersal. Using the headwater stream salamander Gyrinophilus porphyriticus, we tested whether spatial variation in environmental conditions leads to differences in dispersal distances, resulting in spatial variation in the effect of dispersal on inbreeding risk. Using capture-recapture and population genomic data from five streams, we found that dispersal distances were greater in downstream reaches than upstream reaches. Inbreeding risk trended lower for dispersers than nondispersers in downstream reaches but not in upstream reaches. Furthermore, stream reaches did not differ in spatial patterns of individual relatedness, indicating that variation in inbreeding risk was in fact due to differences in dispersal distances. These results demonstrate that environmentally associated variation in dispersal distances can cause the inbreeding consequences of dispersal to vary at fine spatial scales. They also show that selective pressures other than inbreeding avoidance maintain phenotypic variation in dispersal, underscoring the importance of addressing alternative hypotheses in dispersal research.

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Amphibians are useful bioindicators for monitoring aquatic health and the influence of xenobiotics such as endocrine disrupting chemicals. Because aquatic ecosystems experience the majority of global pollution, aquatic organisms are most exposed and vulnerable to endocrine disruptors. Furthermore, penetration of endocrine disruptors into aquatic organisms especially in amphibians is even easier because of more permeable skin, resulting in high bioavailability and bioaccumulation of chemicals. One of the most potent endocrine disruptors is thiourea, which chemically blocks the synthesis of thyroid hormones and prevents metamorphosis in amphibians. We investigated the influence of thiourea on histomorphology of the thyroid gland in Triturus newts at the metamorphic stage, when thyroid hormone concentrations should reach their maximum level. Chronic exposure to thiourea induced hypertrophy and hyperplasia of follicular cells as well as a significant reduction of interstitial tissue. The intensity of the thyroglobulin immunostaining signal significantly decreases upon chronic exposure to thiourea. Successful cross-reactivity of human primary antibody in immunochemical detection of thyroglobulin in Urodela confirms potential homology in thyroglobulin structure throughout the vertebrates.

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