We evaluated the status of a population of Mojave Desert Tortoises (Gopherus agassizii), a threatened species, in the El Paso Mountains of the northwestern Mojave Desert in California, USA. The study area lies north of and adjacent to a designated critical habitat unit for the species, is adjacent to a state park, and is a short distance from the Desert Tortoise Research Natural Area. We randomly sampled 373 1-ha plots from a 239.1-km² area in the mountain range to determine demographic attributes of the population, vegetation associations, predator presence, and human uses. Live and dead G. agassizii and sign (burrows, scats, tracks) occurred on 35.7% of plots. Densities of adults were higher than in adjacent critical habitat, and threats (traumatic injuries, infectious and other diseases) were similar to those reported elsewhere in the geographic range. Signs of human use were evident on 98.4% of plots. We used a multimodel approach to determine distribution of G. agassizii in relation to vegetation, anthropogenic, and predator variables. Vegetation, predators, trash, mining activity, and vehicles were important factors affecting the distribution and intensity of tortoise sign. We concluded that this population is in a downward trend, like other populations in the western Mojave Desert. The high death rate of adults, low population density, high human visitor use, and ongoing decline in the adjacent critical habitat unit indicate that a viable population is unlikely to persist in the study area. The future for the population found in the El Paso Mountains might depend on survival in the adjacent roadless El Paso Mountains Wilderness Area.

Quantifying demographic parameters of freshwater turtle populations at the local scale is necessary in order to understand their natural history and assess their status. To examine whether maritime forest populations display different demographic traits compared to other populations, we studied the freshwater turtle assemblage at Nags Head Woods Ecological Preserve (NHWEP), located on a barrier island of North Carolina. We determined specific demographic traits such as abundance, sex ratio, size distribution, somatic growth, annual survival, and population growth rate of Snapping Turtles (Chelydra serpentina), Yellow-bellied Sliders (Trachemys scripta), Chicken Turtles (Deirochelys reticularia), and Northern Red-bellied Cooters (Pseudemys rubriventris). We determined that most demographic traits of freshwater turtle populations at NHWEP are structured similarly to other populations studied. We found that the population growth rates for three out of the four species analyzed are increasing, indicating expanding populations (with the exception of T. scripta). The annual survivorship rate for D. reticularia was similar to that of many semiaquatic turtles, contradicting previous studies for this species that have reported low annual survival because of reduced longevity. Analyzing multiple demographic traits of different freshwater turtle species within a maritime forest assemblage on a barrier island provides an important baseline on freshwater turtle demographics in unique habitats that are subject to intense environmental stochasticity.

All vertebrates shed the outer layer of their epidermis, usually continuously, but squamate reptiles shed periodically, losing large pieces of this layer at once. While the cellular processes leading to loss of the outer epidermal layer, or shedding, in squamates have been studied in detail, few studies have examined the factors associated with shedding frequency. Shedding is an obligate event, linked to somatic growth and the regeneration of damaged or worn epidermal areas. Another proposed role for periodic shedding in squamates is the removal of ectoparasites and fouling substances stuck on the epidermis. It is unclear whether the removal of ectoparasites and fouling substances is completely passive, only mediated by a fully obligate shedding cycle, or if shedding can be mobilized directly in response to parasite attachment or fouling. To test these hypotheses, we first assessed whether shedding reduced the adherence of parasites to the skin of six different species of geckos by counting mites on the outer epidermis before and after shedding events. Next, we assessed whether shedding was triggered by fouling. Using four species of geckos, we applied artificial substances (marker pen [Sharpie^™], and wood glue [polyvinyl acetate]) to the outer layer of the epidermis and recorded the time between shedding events (shedding interval) compared to unmanipulated controls. There was a clear decrease in parasite loads after shedding events, confirming that shedding reduces adherence of parasites. Our experiments with artificial substances applied to the outer epidermis showed that most gecko species did not change their shedding intervals, regardless of skin-fouling treatment. Hemidactylus frenatus, however, decreased their shedding interval in response to the application of wood glue. Thus, we found that parasites, if present, are removed by shedding, and external fouling can trigger shedding at least in one species of gecko.

The characteristics of a species' evolution can be influenced by its mode of sex determination and, indeed, sex determination mechanisms vary widely among eukaryotes. In nonavian reptiles, the sex determination mechanism has historically thought to be binary, determined either by temperature or genetics. In this study, we add to the growing evidence that sex determining mechanisms in reptiles fall along a continuum rather than existing as a mutually exclusive dichotomy. Using qPCR, we demonstrate that a lizard species, Crotaphytus collaris, possesses sex-based gene dosage consistent with the presence of sex microchromosomes, despite the fact that extreme incubation temperatures can influence hatchling sex ratio. Our results indicate that C. collaris might be the first non-Australian species of lizard having a temperature override of genotypic sex determination, and the first species in which sex switches at both high and low temperatures.

Studies of ecomorphology reveal fascinating examples of how natural selection can mold intra- and interspecific variation in morphology–habitat associations. Despite a growing appreciation for the influence of other factors on these associations (e.g., sexual selection), our understanding of the consequences of spatial variation in their expression remains limited. Given the known ties between habitat selection and thermoregulation, one outcome of such variation might be concomitant divergence in a species' thermal ecological traits. We capitalize on morphology, habitat use, and thermal data collected on adult Sagebrush Lizards (Sceloporus graciosus) from eight populations distributed throughout the species' geographic range to address this limitation. In terms of their morphology, we detected no overall sexual dimorphism in body size, but there was consistent male-biased dimorphism in limb lengths and head width. Although head width and jaw length variation was unrelated to habitat use, larger lizards and lizards with longer legs exploited more open habitats compared to smaller individuals. These ecomorphological patterns were associated with concomitant variation in thermal traits: specifically, substrate temperatures varied geographically, and jointly these temperatures and habitat configuration predicted parallel variation in lizard body temperature. In general, lizards exploiting warmer perches and more heterogeneous habitats attained higher body temperatures. Overall, these findings provide some evidence that lability in thermal traits might be an underappreciated outcome of geographic variation in ecomorphology, possibly providing an important buffer against variable environmental conditions throughout a species' range.

Survival rate is one of the most poorly characterized components of the life history of many species of reptiles, especially snakes. Reproductive activity can increase the risk of mortality. In this study, we examined whether sex-specific reproductive costs affect the survival probability of a viviparous rattlesnake, Crotalus triseriatus, in central Mexico from 2015 to 2018. We used a multimodel inference framework to test two hypotheses: (1) female survival probability should decrease during the late-gestation and birthing period, when females are less mobile and try to achieve stable body temperatures by behavioral thermoregulation; and (2) male survival probability should decrease during the mating season, when males are more actively searching for potential mates. Our data did not support these hypotheses. Mean (±1 SE) monthly survival probability of both males and females was 0.96 ± 0.01, and recapture probability was 0.11 ± 0.01. Annual survival rate was 0.72 ± 0.12. Monthly estimated mean adult population size varied from 16 to 71 adult rattlesnakes. Survival probability was positively correlated with body size. The reproductive costs could have been obscured by the fact that females do not reproduce every year and, therefore, the demands of the mating season are not as tightly linked to survivorship as we hypothesized.

Gape-limited predators, such as snakes, might rely on phenotypic plasticity to cope with variation in prey size, but experimental studies have found mixed evidence for plasticity in snake head morphology. Our study sought to determine whether variation in prey size and feeding rate induce head size plasticity in Northern Water Snakes (Nerodia sipedon). We avoided limitations of previous studies by growing all neonates to a consistent final size (400 mm snout–vent length [SVL]), and uncoupling feeding rate and prey size as potential factors influencing head size through four feeding treatments: big–fast (one large prey item every week), big–slow (one large prey item every other week), small–fast (two small prey items every week), and small–slow (one small prey item every week). Snakes in fast treatments grew faster than snakes in slow treatments, but there were no strong effects of feeding rate or prey size treatments on multiple head size metrics. Females grew faster than males, however, and had longer jaw lengths at 400 mm SVL than did males. Unlike previous studies, our results do not support the presence of phenotypic plasticity in head size in N. sipedon, indicating that head size plasticity in snakes can be species and context specific.

Climatic and geological changes in eastern North America have shaped population history and genetic diversity in many taxa. A common finding of phylogeographic investigations is that southern populations exhibit relatively high levels of phylogeographic structure, whereas northern populations, especially those that have invaded postglacial landscapes, exhibit relatively little genetic differentiation. Here, we describe the results of a phylogeographic investigation of Eastern Red-backed Salamander (Plethodon cinereus), a species that is widely distributed throughout the northeastern United States and southeastern Canada, with roughly three quarters of its range north of the southernmost glacial extent during the last glacial maximum. To investigate patterns of genetic variation, we collected genetic samples from 202 individuals from 107 populations from across the range of P. cinereus, with denser sampling in the southern portion of the range. In total, 4486 base pairs (bp) of DNA were sequenced, including three mitochondrial DNA (mtDNA; 2239 bp) loci and three nuclear (2247 bp) loci. A mix of phylogenetic, population genetic, and clustering approaches were used to explore and summarize patterns of genetic variation. Bayesian phylogenetic analysis of mtDNA recovered six well-supported, geographically cohesive clades that increase in geographic range size from south to north, with a most recent common ancestor estimated at 1.49 million years (95% highest posterior density = 1.09–1.95). The northernmost clade possessed a horseshoe-shaped distribution, including the eastern seaboard, all or part of southeastern Canada, and Michigan, Indiana, and Ohio; thus, this clade was recovered south of the last glacial boundary in both the east and the west. Using simple population genetic tests, we showed evidence of range expansion and isolation by distance in most clades. Using the dispersal-extinction-cladogenesis biogeographic model in RevBayes, we inferred the ancestor of P. cinereus to occupy either the Blue Ridge or the Ridge and Valley physiographic province. In contrast to mtDNA, nuclear loci revealed little phylogeographic structure, and cluster analyses using the nuclear data were not well resolved. Finally, we compare our results with published and unpublished allozyme studies, and we identify several distributional and biogeographic questions that emerge from our findings.

Aplastodiscus musicus is a rare species and the only member of its genus that has not been included in previous phylogenetic studies. This species is known only from its type locality at Serra dos Órgãos National Park in southeastern Brazil, and has not been seen in over 21 yr. Here, we report the re-encounter of an individual of A. musicus at its type locality, describe its advertisement call for the first time, and present a hypothesis concerning its phylogenetic placement. The call of A. musicus is very simple and melodic, composed of one unpulsed note, and emitted at a high repetition rate. It differs from the call of all species of Aplastodiscus and is more similar to those of the A. albofrenatus group. The phylogenetic analysis, based on nuclear and mitochondrial data from all species of Aplastodiscus, recovered A. musicus as the sister taxon of all species currently assigned to the A. albofrenatus group with high support. Our results strongly support the reassignment of A. musicus to the A. albofrenatus group. Previous discussions regarding the evolution of the pericloacal morphology and chromosome number are also revised on the basis of the phylogenetic placement of A. musicus. The re-encounter of A. musicus highlights the importance of increased efforts to search for lost species, especially with the aid of bioacoustics, which permits individual detection and identification at great distances.

We describe a new species of Pristimantis from one of the most isolated regions of Colombia, at elevations of 700–800 m in the Tame River basin at the eastern slope of the Cordillera Oriental in Colombia (Department of Arauca). This locality has been in the grasp of guerrilla groups and right-wing paramilitaries, and as a consequence, this region has been historically inaccessible or risky for researchers. The new species is a diurnal forest dweller, similar to Pristimantis savagei and P. vilarsi. It is distinguished from its congeners by having finely shagreened dorsum skin, areolate ventral skin, moderate tympanic membrane size (length = 37.2–58.8% of eye length), long hind limbs (tibia length = 53.6–63.6% of snout–vent length), and an advertisement call composed of a short single note, while lacking ridges on scapula, tubercles on upper eyelid and heel, and basal webbing in toes. In addition to the new species described herein, we demonstrate that subarticular tubercles display more variation than what is commonly described in taxonomic studies of terraranan frogs.