The woodland and dusky salamanders (Plethodon and Desmognathus) of the southern Appalachians show how molecular studies can deepen our understanding of regional biodiversity. They also show how technological developments can drive shifts in focus, in this case from allele frequencies and population genetics to nucleic acid sequences and phylogenetic inference. This shift has left unanswered important questions about the processes that underlie diversification. Relationships between genetic differentiation and geographic separation provide insight into such questions. Isolation by distance (IBD) relationships in Plethodon and Desmognathus indicate that genetic distance increases more rapidly with geographic separation from north to south in the Appalachian Mountain region of eastern North America. In Desmognathus, genetic divergence appears to increase faster with geographic separation than in Plethodon, perhaps as a consequence of isolation between oviposition sites and larval habitats. Reproductive compatibility may also be retained at higher levels of genetic divergence in Desmognathus than in Plethodon. These patterns deserve further exploration in these and other species, as sequencing techniques are applied in studies of allelic variants at nuclear loci.

There has been increased attention on amphibian declines over the past two decades, and many researchers agree that the primary factor responsible for this decline is habitat fragmentation and degradation. A number of studies have begun to address the impacts of forest management practices on amphibian populations; however, information about behavioral responses of amphibians to forestry practices such as logging is still needed. Using laboratory experiments, I investigated the behavioral choices of Blue Ridge Two-lined Salamanders (Eurycea wilderae) when presented with dry and moist environments (representing logged and unlogged forests) both with and without predators. When no predator was present, E. wilderae preferred a moist environment. When a predator was present in the moist environment, the adult E. wilderae preferred to remain in the less suitable dry environment, while juveniles displayed no clear choice. After logging, E. wilderae are faced with a decision between two adverse environments, with either decision likely resulting in a local population decline. Determining amphibians’ behavioral responses to forest management practices is an important step to developing management plans for forest-dependent species.

Nutrient recycling by fish and amphibians can contribute significantly to ecosystem processes in freshwater ecosystems. Variation in the components that comprise excreta and the factors that control excretion rates may result in differences in the rates and ratios of nutrients excreted by these taxa. These factors can subsequently influence the ecological role of fish and amphibians in freshwater systems. We assessed the composition of excreta of larval Eurycea cirrigera in six headwater streams, and investigated the influence of body size, organismal stoichiometry, and stream nutrient concentrations on mass-specific excretion rates. Excretion components and excretion rates of E. cirrigera were compared to fish in stream and river systems. Excretion of urea comprised the majority of excreted waste in E. cirrigera. This is considerably different from freshwater fish, where the majority of excreted nitrogenous waste is in the form of NH₄. Excretion of NH₄, soluble reactive phosphorus (SRP), and urea by E. cirrigera differed across streams. Body size was the most important predictor of excretion rates of NH₄ and the ratio of N:P in the larvae of E. cirrigera, and no other variables tested influenced the rates of excretion. These estimates reveal larval stream-dwelling plethodontids' excretion rates of inorganic nutrients (NH₄ and SRP) are lower compared to fish in similar systems. However, the contributions of urea (organic forms of nitrogen) are higher. Considering many headwater streams are fishless, stream-dwelling plethodontids, such as E. cirrigera, could represent a primary method of nutrient recycling of limiting nutrients in headwater streams, particularly more labile forms of organic nitrogen.

Salamander species that live entirely in subterranean habitats have evolved adaptations that allow them to cope with perpetual darkness and limited energy resources. We conducted a 26-month mark–recapture study to better understand the individual growth and demography of a population of the Big Mouth Cave Salamander (Gyrinophilus palleucus necturoides). We employed a growth model to estimate growth rates, age at sexual maturity, and longevity, and an open population model to estimate population size, density, detectability, and survival rates. Furthermore, we examined cover use and evidence of potential predation. Individuals probably reach sexual maturity in 3–5 years and live at least nine years. Survival rates were generally high (>75%) but declined during the study. More than 30% of captured salamanders had regenerating tails or tail damage, which presumably represent predation attempts by conspecifics or crayfishes. Most salamanders (>90%) were found under cover (e.g., rocks, trash, decaying plant material). Based on 11 surveys during the study, population size estimates ranged from 21 to 104 individuals in the ca. 710 m² study area. Previous surveys indicated that this population experienced a significant decline from the early 1970s through the 1990s, perhaps related to silvicultural and agricultural practices. However, our data suggest that this population has either recovered or stabilized during the past 20 years. Differences in relative abundance between early surveys and our survey could be associated with differences in survey methods or sampling conditions rather than an increase in population size. Regardless, our study demonstrates that this population is larger than previously thought and is in no immediate risk of extirpation, though it does appear to exhibit higher rates of predation than expected for a species believed to be an apex predator of subterranean food webs.

Studies of plethodontid physiology were quite common in the 1960s, 1970s, and into the early part of the 1980s. Since this time, studies of other aspects of plethodontid biology flourished, while physiological studies lagged behind. Organismal physiology is enjoying a resurgence of interest as researchers attempt to understand threats to biodiversity. In this paper, I outline our current understanding of plethodontid physiology, focusing primarily on energetics, water loss, and endocrine physiology and close by suggesting several avenues for future research. Although we have a good understanding of metabolic physiology in plethodontids, we have considerably fewer data concerning other aspects of plethodontid physiology. I urge researchers to revisit hypotheses and patterns suggested by early studies and expand the breadth of inquiry to multiple levels of ecological organization (individual, population, and species levels). Finally, there is a paucity of data concerning spatial and temporal patterns of physiological variation. Baseline data such as these are critical for formulating and testing broader hypotheses and for developing biologically grounded predictions of responses to anthropogenic stressors.

To understand how rates of growth interact to result in sexual dimorphism in the Black salamander, Aneides flavipunctatus, I conducted a mark–recapture study in Mendocino County, California. Five hundred captures (420 unique animals plus 80 recaptures over four occasions) were measured (body length, head width, head length) and released. Adult males and females are not sexually dimorphic in body length, but are dimorphic in head width; males have wider heads compared to females. From 80 recaptures, growth rates were determined for body length and head size. As expected, juveniles grow faster relative to adults; growth rates decrease as body size increases. Adult males and females have similar growth rates of body length. Males and juveniles have greater head-width growth rates compared to adult females. Head size dimorphism in A. flavipunctatus is a result of a higher head growth rate in males at sexual maturity relative to females. Because body growth rates are not significantly different between adult males and females, adult salamanders of similar size are of similar age. The Von Bertalanffy growth model fit to the mark–recapture growth data conservatively predicts that salamanders of 79 mm snout–vent length are 18 years old. Because of certain assumptions of the model, the oldest salamanders in the population are more likely to be up to 25–30 years old.

Communication of information concerning the sender's quality or intentions is essential for maintaining territories. Receivers that respond to dishonest signals that provide misleading information about quality or intent should therefore be selected against. Honest signals prevent cheating because they are constrained by factors such as the energetic costs of the signal. We tested the hypothesis that “All Trunk Raised” (ATR), a behavior that occurs in territorial contests in terrestrial salamanders, is an honest indicator of aggressive intent. In staged contests between pairs of Ozark Zigzag Salamanders (Plethodon angusticlavius), individuals that performed bites spent more time exhibiting ATR prior to biting than individuals that did not bite. In addition, we examined whether ATR is an energetically costly behavior. In metabolic trials, individuals that performed more ATR produced more CO₂. These results support the hypothesis that ATR is an honest indicator of aggressive intent in this species.

Understanding the role of microhabitats in the ecology of plethodontid salamanders is of utmost importance in the light of recent climate change. Plethodontid species are inherently susceptible to rising temperatures and drier conditions as they utilize cutaneous respiration. Furthermore, many species of plethodontid salamanders have restricted ranges, including species limited to single mountain tops, increasing the consequences of environmental change as their ability to disperse is limited. In this study we compare microhabitat data for a broadly distributed salamander species, Plethodon cinereus, and two microendemic species P. sherando and P. hubrichti. Our analyses evaluate two hypotheses. First, each of these species occupies microhabitat that differs from the available habitat. Second, microhabitat selection of the two microendemic species diverges from the widespread P. cinereus. In addition to testing these hypotheses, we provide additional data to highlight the importance of quantifying thermal microhabitats at different scales. Both P. cinereus and P. sherando were found in microhabitats that differed from randomly selected microhabitats. Moreover, P. cinereus occurred in habitats with high relative humidity and cooler air temperatures, whereas P. sherando occurred in habitats with warmer air temperatures but cooler substrate temperatures. These results suggest that habitat selection may play a role in the persistence of the range of P. sherando in contact zones with P. cinereus. Our data suggest that there may be habitat use differences between P. cinereus and P. hubrichti, but a limited sample size prevents us from making any firm conclusions. We also demonstrated variation in temperatures available in different microhabitats, which highlights the need to better understand microhabitat use as well as how these microhabitats will be affected by climate change.

The isolation and identification of environmental DNA (eDNA) offers a non-invasive and efficient method for the detection of rare and secretive aquatic wildlife, and it is being widely integrated into inventory and monitoring efforts. The Patch-Nosed Salamander (Urspelerpes brucei) is a tiny, recently discovered species of plethodontid salamander known only from headwater streams in a small region of Georgia and South Carolina. Here, we present results of a quantitative PCR-based eDNA assay capable of detecting Urspelerpes in more than 75% of 33 samples from five confirmed streams. We deployed the method at 31 additional streams and located three previously undocumented populations of Urspelerpes. We compare the results of our eDNA assay with our attempt to use aquatic leaf litterbags for the rapid detection of Urspelerpes and demonstrate the relative efficacy of the eDNA assay. We suggest that eDNA offers great potential for use in detecting other aquatic and semi-aquatic plethodontid salamanders.

Mental glands and their associated delivery behaviors during courtship are unique to the plethodontid salamanders. Because previous interpretations of the evolution of these features were conducted using older phylogenetic hypotheses, we reanalyzed these traits with newer courtship descriptions and contemporary phylogenetic methods. Using Bayesian ancestral state reconstruction methods that have been developed since the first phylogenetic analyses were conducted in the mid-1990s, we reconstructed mental gland and courtship behavior evolution on a Bayesian phylogeny of the nuclear gene Rag1. The most probable ancestral condition for plethodontids was resolved as presence of a mental gland. Loss of a mental gland occurred in each subfamily and was recovered as the most probable ancestral condition for the Spelerpinae. In contrast, parsimony reconstruction recovered the presence of a mental gland in the ancestor to Spelerpinae with multiple secondary losses. We hypothesize that that absence of a mental gland is possibly ancestral in some clades (i.e., Spelerpinae) and secondary in others (e.g., paedomorphic Eurycea). The most probable ancestral form of the mental gland is likely to be the large pad-type distributed extensively in Plethodontinae and Bolitoglossinae. Desmognathans have the most unique mental glands, occurring in an anterior protrusion or bifurcated form (in Desmognathus wrighti). Fan-shaped mental glands evolved independently in Eurycea and Oedipina. Small pads arose independently in Bolitoglossinae, Plethodontinae, and Spelerpinae. Head-rubbing behavior for mental gland delivery mode was recovered as the most probable and parsimonious ancestral state for the Plethodontidae, with independent losses of this behavior in Plethodontinae and Spelerpinae. Because head-rubbing was observed in outgroups, we hypothesize that head-rubbing behavior predated mental gland evolution. Pulling, snapping, slapping, and biting behaviors evolved independently in the Plethodontinae and Spelerpinae and are not homologous with head-rubbing. All hypotheses of mental gland and courtship evolution invoke homoplasy.

Gompertz growth functions were fitted to skeletochronological data sets of three species of desmognathine salamanders from an assemblage (Wolf Creek) in the Cowee Mountains of southwestern North Carolina. The results were compared to earlier evaluations of growth in desmognathines from a nearby assemblage (Coweeta) in the Nantahala Mountains. In two of the species, Desmognathus quadramaculatus and D. monticola, larger adult body sizes were attained at Coweeta than at Wolf Creek, whereas adult body sizes of the third species, D. ocoee, were similar in the two populations. Growth in both standard length (snout–vent length) and body mass were evaluated. The early phases of growth, prior to sexual maturation, were similar in the larger D. quadramaculatus and the smaller D. monticola, and higher in both species than in the even smaller D. ocoee. In all three species, growth rates tended to be higher in the Coweeta populations than in those at Wolf Creek. The inflexions of the Gompertz curves for body mass versus age, representing the maximum rates of growth, occurred at or near the age of first reproduction, which is expected, given the tendency for growth to slow at sexual maturation in desmognathines and other salamanders. The results support earlier findings that differences in adult body size between D. quadramaculatus and D. monticola are mainly effects of differences in age at sexual maturation, modulated by a difference in propagule size, as opposed to growth differences. However, the difference in adult size between these species and D. ocoee are joint effects of smaller propagule size, lower growth rate, and earlier maturation in the latter species.

Montane regions are centers of endemism and species richness for many taxa, including plethodontid salamanders. The forces creating and maintaining species' elevational range limits have been extensively studied in members of the genus Plethodon. However, the mechanisms underlying these limits are still poorly understood. Prior work has often focused on range limits from a single perspective, testing ideas of niche conservatism and climatic sensitivity or interspecific competitive interference. Range limits are a complex interaction of both ecological and evolutionary processes. Biotic and abiotic factors may be interacting at different scales, regulating genetic drift, gene flow, and local adaptation. It is only through integrating these ideas across multiple systems that we will be able to begin addressing what limits species elevational distributions.

Although knowledge of the existence of cryptic species dates back hundreds of years, the true extent of cryptic diversity was not discernible until the development of modern molecular techniques. Both homoplasy and morphological conservatism—patterns which result in cryptic taxa—are rampant within the Plethodontidae, the largest salamander family and a taxon rich in cryptic lineages. The first cryptic species of plethodontid, Plethodon websteri, was described in 1979, and the discovery of new cryptic lineages has now become commonplace. Their taxonomic recognition, however, has been controversial, not a surprising result given the differences in methodology—or in the idea of what defines a species—that exist among researchers. Two radiations pinpoint the variation in forces that may drive speciation and the development of cryptic lineages. The Plethodon glutinosus complex represents a non-adaptive radiation characterized by largely parapatric, niche-conserved species. The Desmognathus quadramaculatus complex, on the other hand, is comprised of lineages that have repeatedly evolved the same homoplastic body form that is strongly correlated with niche specialization. Although many cryptic plethodontids exist parapatrically or allopatrically, several occur sympatrically, partitioning niche space more finely than previously imagined. Investigations into the biology of cryptic species should be fruitful in answering questions in both ecology and evolutionary biology and have ramifications for the understanding and conservation of biodiversity.

It is difficult to determine how long salamanders live in the wild. The maximum age estimates using skeletochronology tend to be lower than estimates based on recaptures and size-frequency studies. This discrepancy between techniques suggests it may well be difficult to discern the lines of arrested growth in bones when salamanders are old and their growth rate very low. I review techniques used to estimate longevity, compare age estimates from field (recapture and size frequency comparisons) studies with those from skeletochronology, review growth models, and suggest future work that specifically addresses salamander longevity. Based on observations from captive animals, plethodontids can live a long time (e.g., 36 years). A better understanding of natural longevity is important for understanding the actual age structure of populations and for conservation efforts.

Lungless salamanders in the family Plethodontidae are widely distributed and the most diverse lineage of caudates. Plethodontids occupy forested and freshwater habitats, where they can achieve remarkable abundance and biomass. The majority of tropical plethodontids are arboreal. Though generally considered ground dwelling, a large proportion of temperate species have been observed climbing shrubs, trees, and herbaceous vegetation. Approximately 45% of terrestrial and semi-aquatic (not including permanently aquatic) plethodontid species are known to obligately or facultatively climb vegetation; yet, with the exception of tropical plethodontids, the importance of arboreal habits is generally underappreciated. The potential benefits of arboreality vary based on life history and geography but may include improved olfaction, increased foraging potential, shelter and nesting, and predator avoidance. Constraints on arboreality include increased water loss rates and morphological limitations. Recognition of arboreal habits as a relevant component of salamander ecology is important in rapidly changing landscapes with anthropogenic alterations to midstory and canopy communities.

Since the advent of molecular tools, hybridization has increasingly been recognized as both a common and an evolutionarily important process. Using single nucleotide polymorphism markers from three nuclear genes, we investigated the extent of hybridization between two terrestrial salamanders (Plethodon cinereus and P. electromorphus) at 13 sites in northeastern Ohio, U.S.A. These markers indicated a high degree of gene flow and introgression in these two species (48 of 90 individuals genotyped were classified as hybrids using a Bayesian assignment algorithm). These hybrids included F₁ individuals and backcrosses to both species. These data as well as mitochondrial DNA sequences from hybrids suggest symmetrical hybridization. A multivariate analysis of standard morphological characters and coloration patterns from image analysis demonstrated that hybrids are intermediate in many ways. However, backcrosses proved difficult to separate from parentals, and the extent of hybridization would have been underestimated using morphology and coloration alone. Given the high frequency of hybrids and their broad geographic distribution, we speculate that these two lineages may be in the process of merging back into a single gene pool.

The goal of this study was to document the natural history of salamanders in central Panama and assess their response to drought conditions, which are predicted to become more common as a result of climate change. We conducted 123 transect surveys at night along a concrete trail in a natural area protected by the Panamanian national environmental authority Autoridad Nacional Ambiente (ANAM.) We marked 122 individuals, including two genera and three species, Bolitoglossa biseriata, Oedipina complex, and Oedipina parvipes, from 1 June to 30 July 2013, 10 December 2013 to 6 January 2014, and 1 June to 30 July 2014. All three field seasons took place during a long-term Central American drought. The mean mass of B. biseriata, the most common species of salamander encountered, was 0.8±0.4 g with an average snout–vent length (SVL) of 31.45±5.30 mm. A principal component analysis indicated that B. biseriata utilized all of the available ground-level habitats where surveys were conducted. Bolitoglossa biseriata mostly sat on the leaves of plants anywhere from 14.0–303.8 cm off the ground between 1830 and 0530 h. The season, the air temperature, and the amount of precipitation in the previous 24 h had the largest influence on our detection rate of B. biseriata. Bolitoglossa biseriata in central Panama is nocturnal and most active during the rainy season. Oedipina complex and O. parvipes were equally abundant, but the number of captures for each species varied significantly with season. The Oedipina spp. were found primarily on the ground, although it was not uncommon for them to be climbing on the hand rail or a small plant. A chytrid fungus, Batrachochytrium dendrobatidis (Bd), was detected on B. biseriata and O. parvipes, but we did not detect any mortality resulting from infection. The salamander species at our study site are behaviorally characteristic of their genera, but they have unique color varieties and change their surface activity in correlation with different weather conditions.

Small headwater streams are a common feature of many forested landscapes, and their integrity is considered critical to the maintenance of water quality and biodiversity within broader drainage networks. Although riparian buffer zones are often established to limit disturbance to stream ecosystems from human land use, various buffer zone management strategies may provide effective protection to certain aquatic or semi-aquatic species while only encompassing a portion of core habitat for other species. Thus, an improved understanding of species distributions within riparian forests can be useful for predicting the overall effectiveness of various forest management practices. In this study, we conducted area-constrained surveys for salamanders at 16 plots within terrestrial habitat. We then employed an information-theoretic (AIC) approach to model selection to quantify the distribution of aquatic-breeding Ocoee Salamanders, Desmognathus ocoee, within terrestrial habitat as a function of stream length, width, and/or proximity within the surrounding landscape. Based on a mechanistic model for salamander counts, we estimated that 95% of Ocoee Salamanders are distributed within 79 m of their stream of origin and that relative abundance should decline exponentially with distance into terrestrial habitat. However, a simple model describing salamander counts as an exponential decay with distance from the nearest stream received the strongest support overall, suggesting that this may represent a good predictive model for the distribution of D. ocoee in terrestrial habitat. Due to the prevalence of headwater streams and seeps which do not appear on topographic maps, protecting 95% of core terrestrial habitat around all stream features would require protecting 59.3% of our study landscape. Models describing the spatial distributions of semi-aquatic organisms within terrestrial habitat can be useful for providing spatially explicit density estimates for species conservation or management efforts.

The ability to detect airborne sound using a pressure-transducing tympanic ear has evolved several times over the course of vertebrate history, suggesting that hearing is an advantageous modality and an informative model for sensory evolution. Amphibian hearing is especially interesting because these animals must negotiate water to land transitions. Salamanders are good animal models for the study of hearing, not only because they have a wide range of ear morphologies, but also because they have evolved extratympanic pathways for sound and vibration transmission. Here we suggest that sufficient extratympanic hearing in salamanders and reduced reliance on vocal communication has relaxed selection on the auditory system and allowed for the structural diversity of the salamander ear. Unique among salamanders is the family Plethodontidae, which is not only the most speciose and ecologically diverse family of salamanders, but also possesses a highly derived ear with great inter-specific variation. In this review, we provide an overview of historical and current research on acoustic behavior, auditory anatomy, evolution, and physiology. We highlight plethodontid salamanders as an informative model for study of extratympanic function and auditory evolution.

Animals found in high densities can have significant influence in nutrient cycles of ecosystems. For example, frogs have been known to influence nutrient cycles in tropical forests. However, research understanding the influence of vertebrates in nutrient cycles of North American forest is limited. It has been found that the biomass of terrestrial salamanders (family Plethodontidae) is higher than that of birds, small mammals, and deer in a New Hampshire forest, and recent studies have found prior estimates of terrestrial salamander densities are likely lower than current estimates using sampling and analysis frameworks to account for imperfect detection. A re-evaluation of the impact plethodontid salamanders could have on forest nutrient cycles is therefore justified. We quantified the degree to which a completely terrestrial, lungless salamander (Plethodon albagula; Western Slimy Salamander) constitutes a standing stock of limiting nutrients in a Missouri, USA forest ecosystem. We utilized values of whole-body nutrient composition of carbon (C), nitrogen (N), phosphorus (P), calcium (Ca), and magnesium (Mg) of P. albagula and spatially explicit density estimates to approximate the contribution of P. albagula to forest nutrient cycles. We found that estimates of the standing crop nutrients varied spatially across the landscape and were dictated by density of P. albagula. Standing crop estimates were lower than measures for leaf litter, but often were greater than those previously reported for plethodontid salamanders, birds, and in some cases small mammals and deer in North American forests.

Declines in amphibian populations are due to an array of anthropogenic and natural factors requiring a need to detect and monitor populations that are either in decline or at risk of decline. Physiological biomarkers, such as glucocorticoid stress hormones, present a viable option to monitor stress levels and, thus, the physiological health of vertebrate populations. We performed preliminary experiments necessary for the use of water-borne hormone assays to measure corticosterone (CORT) as an assessment of aspects of chronic stress for the management and conservation of three species of aquatic salamanders in central Texas (Eurycea, Plethodontidae). We examined the time for CORT levels to peak in response to capture and handling in populations of E. nana, E. sosorum, and E. tonkawae. Peak CORT release rates differed among species, with peak releases generally occurring in under 3 h. This highlights the need to obtain a timeline for CORT to mount so that peak rates are captured during the leaching phase. We also examined the responsiveness of the hypothalamic-pituitary-interrenal (HPI) axis using an adrenocorticotropic hormone (ACTH) challenge or exposure to an external stressor (agitation). Eurycea sosorum (one population) and E. tonkawae showed HPI responsiveness. To examine the relationship between field and laboratory CORT release rates, we compared baseline CORT release rates between captive and wild-caught populations of all three species. Once the preliminary studies have been performed, water-borne CORT release rates can be an effective biomarker to monitor whether a population is experiencing chronic stress. Water-borne hormone collection also allows for repeated sampling of individuals over time. Our experiments provide a foundation for future studies relating stress to HPI responsiveness in aquatic Eurycea, which, in turn, will help inform management of both wild and captive populations.

We have examined the morphology of the skeletal elements involved in constricted-based tail autotomy in Neotropical plethodontid salamanders of the genus Bolitoglossa. Observed variation in the transverse processes of the first caudal vertebra ranges from a relatively generalized condition, similar to that seen in North American species, to morphologically specialized structures found only in tropical species. Here we present evidence that most species of Bolitoglossa have evolved hypertrophied, reversed transverse processes whose shape and size go beyond what is necessary for structural support in constricted-based tail autotomy and allow the autotomized tail to be used as an anti-predator weapon. We discuss the evolutionary implications of this mechanism.

Ring species are widely recognized as one of the best natural illustrations of species formation. A ring species is a circular arrangement of populations with one boundary characterized by reproductive isolation, but intergradation among populations elsewhere. They form when populations disperse around a central barrier and form a secondary contact characterized by reproductive isolation. Ring species are often presented as a taxonomic conundrum, because the presence of a single boundary exhibiting reproductive isolation leaves the ring of populations uncomfortably situated between one and two species. Here we review the ring species concept, with a focus on the salamander Ensatina eschscholtzii and the Greenish Warbler, Phylloscopus trochiloides. We argue that ring species demonstrate the gradual nature of species formation, and thereby illustrate the model of species formation originally put forth by Darwin. We also argue that ring species have become overly idealized, with a focus on strict criteria to the detriment of evolutionary lessons. Like all models of evolutionary change, the ring species concept is an oversimplification, and an ideal ring species has never been found. Finally, we review ring species in light of the general lineage concept of species, and argue that ring species status, while nicely accommodated by recognizing a single species, is independent of taxonomy. The essential features of a ring species are a biogeographic history resulting in a ring-like distribution, and the presence of a single species border characterized by reproductive isolation. Under the general lineage concept, reproductive isolation is a contingent, but not necessary, property of evolutionary lineages. Whether one considers a ring species complex to be one species or many does not change the evolutionary message, and the problems (and lessons) presented by ring species do not go away with taxonomic changes.

The size of an organism is perhaps its most overt physical characteristic, and variation in body size has long been of interest to biologists. Bergmann's rule has been actively studied and debated for more than 150 years. Despite this long history, the generality and applicability of Bergmann's rule to ectothermic organisms generally, and to plethodontid salamanders specifically, has resulted in an extensive and conflicting literature. Regardless of mechanism, clinal variation in body size has been widely observed in plethodontid salamanders and other ectothermic vertebrates. In this study, we assessed the change in adult body size of four plethodontid salamanders (Desmognathus imitator, D. ocoee, D. wrighti, and Plethodon jordani) across a 1,350 m elevational gradient in Great Smoky Mountains National Park. Using 1,293 observations of salamanders at 25 sites, we found clear and significant patterns of increasing adult body size with elevation in all four species. Average rates of increase ranged from 1.09% to 3.98% per 100 m elevation gain. We found that elevation significantly covaried with maximum and mean temperature, as well as average annual precipitation. Our study reinforces previous research describing increases in plethodontid salamander body size with elevation, but also extends these findings to fully terrestrial, direct-developing species. However, the mechanisms underlying the observed pattern are still unclear and highlight an important area for future research. As a critical life history characteristic, an understanding of geographic variation in body size is important for assessing current population dynamics, as well as the potential effects of future climate changes.

In recent years, many molecular endocrine mechanisms that regulate tissue morphogenesis have been detailed in laboratory amphibian models. However, most of these pathways have not been examined across more closely related species to understand how deviations in endocrine pathways may have contributed to amphibian diversification. The timing of metamorphosis and maturation vary extensively across plethodontid salamanders (including direct developing, biphasic, and paedomorphic species), making them an ideal system for analyzing the evolution of endocrine mechanisms in a phylogenetic context. Recent phylogenetic-based reconstructions concluded that ancestral plethodontids were likely direct developers, and free-living larval periods were independently derived multiple times within this family. Furthermore, within one clade (Spelerpini) there have been multiple independent transitions from biphasic (metamorphic) to paedomorphic developmental modes. This inspires the question: What endocrine/developmental mechanisms govern these extreme life history transitions? Prior endocrine models for the evolution of direct development and paedomorphosis have been largely based on the ontogenetic timing of thyroid hormone release and/or thyroid hormone responsiveness of target tissues. Here I review endocrine pathways that influence metamorphosis and maturation in laboratory amphibians (Clawed frog and Axolotl) and other species, and develop a model that integrates prior thyroid hormone-based patterns with other endocrine axes. This integrated framework incorporates developmental shifts that result from plasticity or evolution in the timing of hatching, metamorphosis, and maturation, and can be used to test mechanistic changes that underlie life history variation of plethodontids and other salamanders.

While salamanders have a predominantly north-temperate distribution, one of the most stunning radiations of species occurred in the only group to significantly penetrate the tropics, the bolitoglossines. Biogeographic hypotheses for the group have evolved as a result of the discovery of new species and lineages, from approximately 30 species in a single genus in 1926 to nearly 300 species in 14 genera today. Molecular phylogenies provide an important tool with which to test long-standing biogeographic hypotheses. Divergence dating analyses and parametric biogeographic analyses, together with a changing understanding of the taxonomy of the bolitoglossines and new geological evidence from Mesoamerica, call into question several long-standing hypotheses related to the arrival and diversification of the bolitoglossines in Central and South America. We briefly review the geology of Mesoamerica, with an emphasis on regions of high salamander diversity, and discuss how molecular phylogenies and new species discoveries have changed our perception of the history of this salamander radiation.

Studying morphological features in addition to ecological characteristics of co-occurring species can provide insight into interactions between species. Determining factors that influence interactions between species provides a framework for understanding evolution in natural environments. Plethodontid salamanders are model taxa frequently used to study species interactions in regard to competition, coexistence, and exclusion. Past studies have suggested that P. ventralis and P. websteri exhibit character displacement in color and may competitively interact when in sympatry. We studied P. ventralis and P. websteri at a sympatric location in Jefferson County, Alabama and compared this population to allopatric populations of each species to identify whether these species differed in morphology and diet, which are indicators for interspecific competition. We found that P. ventralis and P. websteri differed in head shape, in general, and that head shape differed among populations within species. However, we did not find significant shifts within species between allopatric and sympatric locations, which would have indicated character displacement or convergence. Furthermore, species did not differ in diet at any of the studied locations. Interestingly, we discovered that variation in head shape among locations of both species, regardless if the location was allopatric or sympatric, was significant. This result reiterates the importance of including population variation in the context of character displacement and competition. Results of this study can be placed in a robust theoretical context developed from numerous studies of salamander interactions and, thus, lead to a greater understanding of population variation, competition, and species interactions between ecologically similar species.

A new species of Moenkhausia is described from the upper Rio Juruena, Rio Tapajós basin, Mato Grosso, Brazil. The new species is diagnosed from all congeners, except M. eurystaenia, M. heikoi, and M. phaeonota, by the presence of a dark, straight, broad stripe extending from the opercle to the middle caudal-fin rays. The new species can be distinguished from M. heikoi and M. phaeonota by having 18–20 branched anal-fin rays and from M. eurystaenia by having a narrow longitudinal dark line along the horizontal septum, starting at the vertical through the pelvic-fin origin. The presence of a conspicuous dark blotch on the ventral portion of the opercle and on the ventral portion of the vertical arm of the preopercle is also useful to distinguish the new species from most congeners.

A new species of Hyphessobrycon is described from the Rio Papagaio, a tributary of the Rio Juruena, Rio Tapajós basin, Brazil. The new taxon can be distinguished from its congeners by having a well-defined and relatively narrow dark midlateral stripe on body extending from the upper half of the posterior margin of the eye to the middle caudal-fin rays, absence of a humeral blotch, 16–19 branched anal-fin rays, 2–4 maxillary teeth, six branched pelvic-fin rays, and the absence of dark pigmentation crossing the eye. Hyphessobrycon cyanotaenia, a species described from few specimens from the aquarium trade without precise locality, is redescribed herein based on extensive material, and its known distribution is discussed and rectified from the original description.

Accurate expedient species identification of deceased sturgeon (Acipenseridae) when external physical characteristic analysis is inconclusive has become a high priority due to the endangered or threatened status of sturgeon species around the world. Examination of otoliths has provided useful information to aid in population management, age and size-class analysis, understanding predator–prey interactions, and archeological research in other fish species. The relationship between otolith characteristics and sturgeon species has remained unknown. Therefore, we analyzed the shape of otoliths from the eight species of sturgeon found in North America to test the utility of otolith characteristic morphology in species identification. There were distinct differences in the size and shape of the otoliths between species of sturgeon with little shape variation among individuals of the same species. The relationship between otolith length axes was linear, and most of the variability was explained by a Log (axis 1) transformation of the x and y axes (r² = 0.8983) using the equation y = 0.73x 0.0612. Images of otoliths from all eight North American species are presented to assist in the identification process.