Plethodontid Salamanders Research Articles

Levels of Sex Steroids in Plethodontid Salamanders: A Comparative Study Within the Genus Aneides.

Derived monomorphism is a condition in which males and females are phenotypically similar, but the similarity is derived. Derived monomorphism typically evolves from sexual dimorphism or from a different monomorphic state. We examined the hormonal basis of derived monomorphism in the salamander genus Aneides (Plethodontidae). We reject our hypothesis that circulating levels of androgens explain the derived traits, such as enlarged jaw musculature, in females (some would call them "male-like traits"). There was no clear pattern of differences in androgen levels or degree of dimorphism in androgen levels, between the sexually dimorphic Aneides hardii and the other, derived monomorphic, species studied. Concentrations of testosterone and dihydrotestosterone were higher in males than in females in all species examined. The degree of sexual dimorphism in androgen level was also consistent among the species studied. Levels of androgens in female plethodontids have not been previously reported.

Methylmercury Concentrations More Strongly Associated With Trait Variation Than Food Web Position in Plethodontid Salamanders.

Salamanders serve as bioindicators of mercury (Hg) in both terrestrial and aquatic habitats and are an important link in the food web between low-trophic prey and higher-trophic predators. We investigated the drivers of methylmercury (MeHg) exposure in three common plethodontid salamander species in New York State, USA, including comparisons among regions, habitat types (terrestrial and semiaquatic), and color morphs of Plethodon cinereus (striped and unstriped). Nonlethal tail samples were collected from one terrestrial species (P. cinereus) and two semiaquatic species (Eurycea bislineata and Desmognathus spp.) in the Adirondack Mountains (ADK) and the Finger Lakes National Forest (FLNF) regions. Samples were analyzed for MeHg and stable isotopes, including δ15N and δ13C which are proxies of trophic position and diet, respectively. Despite elevated biota Hg concentrations typically found in the ADK, salamander MeHg concentrations did not differ by region in the terrestrial species and one of the semiaquatic species. In addition, diet and trophic level did not explain MeHg exposure in salamanders. Semiaquatic salamanders exhibited higher MeHg concentrations than terrestrial salamanders in the FLNF only. Within species, only snout-vent length predicted MeHg concentrations in E. bislineata with few other variables significant as predictors of MeHg concentrations in path models. Among P. cinereus individuals in the FLNF, the striped morph had greater MeHg concentrations than the unstriped morph, and food web tracers were not different between morphs. Overall, New York State salamander Hg concentrations were elevated compared to other locations where these species are present. The present study establishes baseline Hg data in salamanders for future assessments of changes in Hg bioavailability to forests of New York State. Environ Toxicol Chem 2024;43:2045-2057. © 2024 SETAC.

Range-wide salamander densities reveal a key component of terrestrial vertebrate biomass in eastern North American forests.

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.

The role of familiarity in shelter site fidelity: insights from a mesocosm experiment with a plethodontid salamander

Behavioral adaptation is one of the first responses put in play by individuals to buffer environmental variations and to maintain homeostatic equilibrium with their environment. Microhabitat selection is pivotal for maximizing fitness, survival and reproduction, but how individuals process and exploit information acquired from the environment to make future microhabitat choice is yet understudied. In this study, we used outdoor mesocosms in which we introduced Strinati’s cave salamanders (Speleomantes strinatii), to assess their behavioral patterns of shelter site fidelity. In each mesocosm three microhabitats were available to the salamanders: the leaf litter, a log and a rock. A total of 22 salamanders were tested over an 8-day period, 11 in autumn and 11 in spring. Salamanders shelter site fidelity was driven by both microhabitat humidity and previous experience obtained in the mesocosm. In our experiment, the time spent in the mesocosm was the main factor influencing shelter site fidelity, suggesting that previous experience and familiarity are important in salamanders’ behavioral adaptation. Therefore, cave salamanders are capable of learning from experience when selecting their shelters, a behavior that could also be relevant during migration, colonization of new environments and adaptation to climate change.

Introduction to the Special Issue on the 8th Conference on the Biology of Plethodontid Salamanders

Introduction to the Special Issue on the 8th Conference on the Biology of Plethodontid Salamanders

Impacts of Wildfire Burn Severity on Plethodontid Salamander Populations of Great Smoky Mountains National Park

Impacts of Wildfire Burn Severity on Plethodontid Salamander Populations of Great Smoky Mountains National Park

Androgen Receptors in the Dermal Glands of Male and Female Ouachita Dusky Salamanders.

The presence of androgens in female development is an important, yet often overlooked, topic. We tested for the presence of androgen receptors (ARs) in the dermal glands of male and female Desmognathus brimleyorum, a plethodontid salamander. This species engages in a courtship behavior called the tail-straddling walk. During this process, communication between males and females is hypothesized to be facilitated by pheromones secreted from modified granular glands (MGGs) on the dorsal tail base, where the female's chin is positioned. These glands are present not only dorsally but also laterally and ventrally on the tail of both males and females. Using immunohistochemistry with a polyclonal antibody, ARs were located in the MGGs of both sexes. Males had a higher percentage of immunopositive cells per MGG than females. The presence of ARs in both sexes highlights the similarity between MGGs in males and females and suggests androgens play a role in female gland function. Furthermore, our results suggest courtship communication is bidirectional, and females have a more active role, signaling the male, than previously described.

Survey of southern Missouri Plethodontidae in Ozark caves

Plethodontidae is a large family of salamanders with a distribution ranging from eastern North Americato northern South America. Three genera and nine species occur in Missouri, most of which are typically found in cavesfor at least part of their lives. These species have been recorded to emerge from hibernation in early April and throughoutMay. This study shares the species abundance and diversity in ten Missouri Ozark caves: seven near St. Louis andthree near Springfield. Each cave was surveyed at least once between November 2021 and September 2022 using visualencounter surveys. Observational data were recorded without handling any individuals to minimize disturbance. Thethree caves near St. Louis had few to no salamanders present in early April, despite optimal weather conditions, buttended to have larger populations throughout the summer. Two caves near Springfield held at least a dozen individualsof multiple species in mid-April. Few individuals were recorded in the most southwestern cave sampled, potentiallydue to pollution or recent flooding. Our findings could aid others studying plethodontid salamanders to determine theprime conditions for emergence from hibernation, optimal habitats for different species in each cave zone, and potentialbiological or chemical impacts that could affect salamander abundance in caves.

Effect of hydration state on locomotor performance and water searching behavior of the terrestrial lungless salamander Bolitoglossa ramosi

AbstractBolitoglossa ramosi is a terrestrial plethodontid salamander particularly active during cloudy nights with high relative humidity in the environment. In this work, we tested the hypotheses that: (1) the hydration state of B. ramosi directly affects its locomotor performance; (2) dehydrated salamanders spend less time to find a water source than hydrated salamanders and (3) dehydrated salamanders find a water source in fewer attempts than hydrated individuals. To evaluate these hypotheses, salamanders at different levels of body hydration were used for an experiment of maximum locomotor performance, and a behavioral assessment test for searching a water source that was randomly located in one of the eight arms of a labyrinth. We found that salamanders hydrated at 95% had a greater locomotor performance (speed) than those hydrated at 85% and 75%. On the other hand, salamanders hydrated at 75% found the water source faster than those hydrated at 95%, although there was not a significant difference between these two groups of salamanders tested in the number of arms visited to find the water source. According to our results, we propose that dehydration in salamanders could be a causal factor for the inactivity of these animals during low levels of environmental humidity, and can also motivate a faster response to find a water source. In addition, we postulate that B. ramosi seems to use a random searching behavior to locate a water source as both hydrated and dehydrated salamanders find it after several attempts.

Different patterns of introgression in a three species hybrid zone among European cave salamanders.

Hybrid zones occur where genetically distinct populations meet, mate and produce offspring with mixed ancestry. In Plethodontid salamanders, introgressive hybridization is a common phenomenon, where hybrids backcross with parental populations leading to the spread of new alleles into the parental genomes. Whereas many hybrid zones have been reported in American Plethodontid salamanders, only a single hybrid zone has been documented in European plethodontids so far, which is located at the Apuan Alps in the Italian Peninsula. Here, we describe a previously unreported hybrid zone in the Northern Apennines involving all the three Plethodontid salamander species inhabiting the Italian Peninsula. We found 21 new Speleomantes sites of occurrence, from a hitherto unexplored area located at the boundaries between three Speleomantes species ranges. Using mitochondrial (Cytb and ND2 genes) and nuclear markers (two diagnostic SNPs at the NCX1 gene), we revealed a three-way contact zone where all the three mainland species hybridize: S. strinatii, S. ambrosii and S. italicus. We observed a strong mitonuclear discordance, with mitochondrial markers showing a conspicuous geographic pattern, while diagnostic nuclear SNPs coexisted in both the same populations and individuals, providing evidence of hybridization in many possible combinations. The introgression is asymmetric, with S. italicus mitogenome usually associated with S. a. ambrosii and, to a lesser extent, to S. strinatii nuclear alleles. This finding confirms that Plethodontid are a group of choice to investigate hybridization mechanisms and suggests that behavioural, genetic and ecological components may concur in determining the direction and extent of introgression.

Presence of sodefrin precursor-like factor pheromone candidates in mental and dorsal tail base glands in the plethodontid salamander, Karsenia koreana.

Plethodontid salamanders are well known for their distinct courtship rituals and the associated pheromonal signaling. However, little is known about pheromones produced in the lone Asian plethodontid species Karsenia koreana. Here, we examined the localization patterns of proteins of the sodefrin precursor-like factor (SPF) pheromone system in K. koreana. Using an antibody generated against SPF proteins from another plethodontid, Desmognathus ocoee, we tested three types of skin glands in K. koreana males via immunohistochemistry: the mental gland and two types of dorsal tail base glands-caudal courtship glands and dorsal granular glands. SPF immunoreactivity was detected in the known courtship gland, the mental gland, as well as granular glands, but not in caudal courtship glands. Due to immunoreaction specificity, we hypothesize the proteins of the SPF system in K. koreana and D. ocoee are structurally and functionally related and are used as courtship pheromones in K. koreana. Also, we hypothesize that K. koreana males transmit SPF to the female during the tail-straddling walk via dorsal granular glands. Finally, K. koreana male caudal courtship glands may be producing SPF proteins that are not recognized by our SPF antibody or these glands may play a different role in courtship than anticipated.

Microclimate species distribution models estimate lower levels of climate-related habitat loss for salamanders

Species distribution models (SDMs) largely rely on free-air temperatures at coarse spatial resolutions to predict habitat suitability, potentially overlooking important microhabitat. Integrating microclimate data into SDMs may improve predictions of organismal responses to climate change and support targeting of conservation assets at biologically relevant scales, especially for small, dispersal-limited species vulnerable to climate-change-induced range loss. We integrated microclimate data that account for the buffering effects of forest vegetation into SDMs at a very high spatial resolution (3 m2) for three plethodontid salamander species in Great Smoky Mountains National Park (North Carolina and Tennessee). Microclimate SDMs were used to characterize potential changes to future plethodontid habitat, including habitat suitability and habitat spatial patterns. Additionally, we evaluated spatial discrepancies between predictions of habitat suitability developed with microclimate and coarse-resolution, free-air climate data. Microclimate SDMs indicated substantial losses to plethodontid ranges and highly suitable habitat by mid-century, but at much more conservative levels than coarse-resolution models. Coarse-resolution SDMs generally estimated higher mid-century losses to plethodontid habitat compared to microclimate models and consistently undervalued areas containing highly suitable microhabitat. Furthermore, microclimate SDMs revealed potential areas of future gain in highly suitable habitat within current species’ ranges, which may serve as climatic microrefugia. Taken together, this study highlights the need to develop microclimate SDMs that account for vegetation and its biophysical effects on near-surface temperatures. As microclimate datasets become increasingly available across the world, their integration into correlative and mechanistic SDMs will be imperative for accurately estimating organismal responses to climate change and helping environmental managers tasked with spatially prioritizing conservation assets.

Ramosin: The First Antibacterial Peptide Identified on Bolitoglossa ramosi Colombian Salamander.

The discovery and improvements of antimicrobial peptides (AMPs) have become an alternative to conventional antibiotics. They are usually small and heat-stable peptides, exhibiting inhibitory activity against Gram-negative and Gram-positive bacteria. In this way, studies on broad-spectrum AMPs found in amphibians with the remarkable capability to regenerate a wide array of tissues are of particular interest in the search for new strategies to treat multidrug-resistant bacterial strains. In this work, the use of bioinformatic approaches such as sequence alignment with Fasta36 and prediction of antimicrobial activity allowed the identification of the Ramosin peptide from the de novo assembled transcriptome of the plethodontid salamander Bolitoglossa ramosi obtained from post-amputation of the upper limb tissue, heart, and intestine samples. BLAST analysis revealed that the Ramosin peptide sequence is unique in Bolitoglossa ramosi. The peptide was chemically synthesized, and physicochemical properties were characterized. Furthermore, the in vitro antimicrobial activity against relevant Gram-positive and Gram-negative human pathogenic bacteria was demonstrated. Finally, no effect against eukaryotic cells or human red blood cells was evidenced. This is the first antibacterial peptide identified from a Colombian endemic salamander with interesting antimicrobial properties and no hemolytic activity.

A new arboreal Pseudoeurycea (Caudata: Plethodontidae) from the Sierra de Zongolica, Veracruz, Mexico

We describe a new species of plethodontid salamander of the genus Pseudoeurycea from the Sierra de Zongolica, Veracruz, Mexico. The new species is distinguished from all other species in the genus by morphological and genetic features and by coloration. Based on a mtDNA phylogeny, the new species belongs to the Pseudoeurycea juarezi group and is most closely related to P. ruficauda from the Sierra Mazateca in northern Oaxaca. The newly described salamander increases the number of species of plethodontid salamanders from Veracruz to 43 and those recognized from Mexico to 140.

Aerial maneuvering by plethodontid salamanders spanning an arboreality gradient.

Wandering salamanders (Aneides vagrans) inhabit the crowns of the world's tallest trees, taking refuge in epiphytic fern mats within these complex arboreal environments. These salamanders readily jump from the canopy when disturbed and maintain stable postures while falling via fine adjustments of the limbs and tail in lieu of dedicated aerodynamic control surfaces, thus reliably carrying out non-vertical descent. Here, we examined the aerial behavior and performance of A. vagrans and three other species of plethodontid salamander across a habitat gradient of arboreality by recording salamanders falling from short heights and moving within the jet of a vertical wind tunnel. Kinematic performance of aerial behavior in plethodontid salamanders was correlated with a gradient of arboreal habitats; moreover, salamanders from arboreal niches were more effective in slowing and redirecting descent compared with other salamanders. Aneides vagrans and the closely related Aneides lugubris consistently engaged in parachuting and gliding when falling; their trajectories were very steep, but were sufficiently angled to enable contact with either the home trunk or nearby branches during falls or jumps from great heights. Aerial maneuvering in arboreal salamanders is similar to that seen in other vertebrates capable of non-vertical and controlled descent, suggesting that the long limbs and active tail of these arboreal plethodontids (often cited as adaptations for climbing) may also contribute to parachuting and gliding when falling from trees. These aerial behaviors within the redwood canopy warrant further investigations into other canopy residents that lack conspicuous surfaces for aerodynamic control.

Speciation Hypotheses from Phylogeographic Delimitation Yield an Integrative Taxonomy for Seal Salamanders (Desmognathus monticola).

Significant advances have been made in species delimitation and numerous methods can test precisely defined models of speciation, though the synthesis of phylogeography and taxonomy is still sometimes incomplete. Emerging consensus treats distinct genealogical clusters in genome-scale data as strong initial evidence of speciation in most cases, a hypothesis that must therefore be falsified under an explicit evolutionary model. We can now test speciation hypotheses linking trait differentiation to specific mechanisms of divergence with increasingly large data sets. Integrative taxonomy can, therefore, reflect an understanding of how each axis of variation relates to underlying speciation processes, with nomenclature for distinct evolutionary lineages. We illustrate this approach here with Seal Salamanders (Desmognathus monticola) and introduce a new unsupervised machine-learning approach for species delimitation. Plethodontid salamanders are renowned for their morphological conservatism despite extensive phylogeographic divergence. We discover 2 geographic genetic clusters, for which demographic and spatial models of ecology and gene flow provide robust support for ecogeographic speciation despite limited phenotypic divergence. These data are integrated under evolutionary mechanisms (e.g., spatially localized gene flow with reduced migration) and reflected in emergent properties expected under models of reinforcement (e.g., ethological isolation and selection against hybrids). Their genetic divergence is prima facie evidence for species-level distinctiveness, supported by speciation models and divergence along axes such as behavior, geography, and climate that suggest an ecological basis with subsequent reinforcement through prezygotic isolation. As data sets grow more comprehensive, species-delimitation models can be tested, rejected, or corroborated as explicit speciation hypotheses, providing for reciprocal illumination of evolutionary processes and integrative taxonomies. [Desmognathus; integrative taxonomy; machine learning; species delimitation.].

Optimizing monitoring of an endemic terrestrial salamander (Speleomantes ambrosii): comparing cost-effectiveness of different methods for abundance estimation

In order to correctly plan conservation and management of animal populations, it is fundamental to obtain reliable information on population abundance using cost-effective monitoring methods. In the case of small terrestrial vertebrates, capture–mark–recapture, removal sampling and counts of unmarked individuals have proven to be reliable techniques to estimate population abundance. In the present study, we applied a multinomial N-mixture modelling approach, performed through a double-observer sampling protocol, to estimate population size of the endemic terrestrial salamander Speleomantes ambrosii. We aimed at comparing cost-effectiveness of this protocol with those of other estimation methods (i.e., capture–mark–recapture and removal sampling), with particular attention to management and monitoring guidelines. The double-observer multinomial N-mixture protocol was the most cost-effective among the different methods: given its ease of application and cost-effectiveness, we encourage its employment for long-term monitoring and conservation plans of the near-threatened plethodontid salamander Speleomantes ambrosii.

Potential Distribution and Connectivity for Two Plethodontid Salamanders: Conservation Areas and Landscape Corridors for Two Endemic Species of México and Guatemala.

Habitat loss is one of the most important threats to biodiversity; it alters the habitat connectivity of species and is among the main causes of the global amphibian extinction crisis. Identifying the potential areas of distribution and connectivity of species is of the utmost importance so that informed decisions can be made for the conservation of vulnerable amphibian populations. In this study, we performed species distribution models and used circuit theory to model omnidirectional connectivity for two plethodontid salamanders of conservation concern distributed in the forests of Chiapas, Mexico, and Guatemala (Bolitoglossa franklini and Bolitoglossa lincolni). Potential distribution maps show an affinity for well-preserved montane forests for both species. Likewise, we found that the niches of the species are not similar. The connectivity models show that the main areas of connectivity are in the Meseta Central de Chiapas, Sierra Madre de Chiapas, and the Cordillera Volcánica Guatemalense, in this last range, important areas of connectivity were located, as well as least-cost paths and barriers to the movement of both species. We identified that important areas of climatic suitability and connectivity are not within the protected natural areas and may be threatened by the increasing influence of anthropogenic activities. The results of our study show the importance of preserving the regional forests to ensure the persistence of species with arboreal habits and high sensitivity to habitat transformation, as well as to recognize and prioritize potential areas for management and protection in both southern Mexico and Guatemala.

Developmental basis of evolutionary lung loss in plethodontid salamanders.

One or more members of four living amphibian clades have independently dispensed with pulmonary respiration and lack lungs, but little is known of the developmental basis of lung loss in any taxon. We use morphological, molecular, and experimental approaches to examine the Plethodontidae, a dominant family of salamanders, all of which are lungless as adults. We confirm an early anecdotal report that plethodontids complete early stages of lung morphogenesis: Transient embryonic lung primordia form but regress by apoptosis before hatching. Initiation of pulmonary development coincides with expression of the lung-specification gene Wnt2b in adjacent mesoderm, and the lung rudiment expresses pulmonary markers Nkx2.1 and Sox9. Lung developmental-genetic pathways are at least partially conserved despite the absence of functional adult lungs for at least 25 and possibly exceeding 60 million years. Adult lung loss appears associated with altered expression of signaling molecules that mediate later stages of tracheal and pulmonary development.

Short‐term responses of riparian salamander populations to wildfire in the Southern Appalachians

AbstractWildfire is a natural disturbance within many forest ecosystems and is rapidly becoming more frequent and severe because of the combination of historical fire suppression and climate change. In Southern Appalachian hardwood forests, there is a limited understanding of how salamander populations respond to wildfire, despite their high diversity and abundance in forest ecosystems. We expected populations of lungless, plethodontid salamanders to respond negatively to wildfire and the drier microhabitat conditions in burned habitat. We evaluated the effect of fire on 3 plethodontid salamander species (Blue Ridge two‐lined salamander [Eurycea wilderae], Ocoee salamander [Desmognathus ocoee], red‐legged salamander [Plethodon shermani]) with different life histories from 2017–2019 following a wildfire in a Southern Appalachian riparian forest in North Carolina, USA. We estimated differences in abundance, frequency of adults in the population, and terrestrial distribution in relation to streams between burned and reference riparian forest sites. Wildfire had negative effects on the abundance of semi‐aquatic species, but temporal patterns differed by species. Abundance of the Blue Ridge two‐lined salamander was lower in burn sites than reference sites immediately after fire, followed by a gradual convergence towards reference‐site densities. Conversely, Ocoee salamanders had a time‐lagged response, where we observed significantly lower densities in burn sites relative to reference sites for only 2 years after fire. We did not observe strong responses of red‐legged salamander abundance to fire. There were no consistent patterns in how the percentage of adults in reference or burn sites differed over time, suggesting that population responses to burn vary by species. Finally, we observed adults of all species and juveniles of semi‐aquatic species farther from streams in burn sites. Our findings suggest plethodontid salamander communities may tolerate riparian wildfires, although longer‐term studies are required to understand how long it takes for patterns of population size structure and habitat use to converge with those in unburned reference sites.