The squamates occur in a variety of climates from tropical to Arctic regions. Being poikilotherms, snakes and lizards in temperate regions, and high elevation tropical environments, must adjust their reproductive biology to reproduce at a time that optimizes offspring survival. The two major components of the reproductive cycle in both males and females are gametogenesis and mating. The reproductive cycle of males is the focus of this study. In snakes in temperate climates, sperm production (spermatogenesis) may occur immediately prior to mating (prenuptial spermatogenesis) or following mating (postnuptial spermatogenesis). In postnuptial spermatogenesis, sperm are produced following the mating season and stored in the efferent testicular ducts (primarily the ductus deferens) until the following spring mating season. Given that most recent phylogenetic reconstructions resolve snakes as a monophyletic group of highly specialized lizards, it is generally assumed that lizards have spermatogenic cycles similar to snakes. Lizard spermatogenic cycles are often described as prenuptial or postnuptial. We propose that the major difference between snake and lizard spermatogenic cycles is the presence of postnuptial spermatogenesis in snakes and the absence of true postnuptial spermatogenesis in lizards. Our interpretation of lizard spermatogenic cycles suggests that all lizards have prenuptial spermatogenesis (i.e., sperm are produced immediately prior to mating). If fertilization occurs months after mating, the female, and not the male, stores the sperm until spring ovulation and fertilization. Using a variety of analytical tools, we analyzed the reproductive strategies of snakes and lizards, and we have concluded that they differ in fundamental ways. Most notably, prenuptial spermatogenesis is the ancestral condition for Squamata with continuous spermatogenesis evolving multiple times independently within lizards and snakes. We also found that postnuptial spermatogenesis evolved early in the evolutionary history of snakes but, we argue, has never evolved in lizards. We suggest that the evolutionary origin of snakes may account for the differences observed in snake versus lizard reproductive cycles, and we present a scenario for the evolution of snake reproductive cycles.

Surveys and analyses of anatomical characters have allowed researchers to describe a wealth of anatomical features and contribute to our evolutionary understanding of fishes for centuries. However, most of these studies have focused on specific lineages or families rather than the broader evolutionary relationships. As such, there has been a lack of progress inferring higher-level relationships among percomorphs. With the use of large-scale DNA-based methods in multiple studies over the past two decades, the backbone of the phylogeny of fishes is becoming increasingly understood. Taking this DNA-based phylogenetic backbone into account, we have the opportunity to integrate discrete morphological characters and DNA sequence data to test earlier topologies and provide new and improved hypotheses of relationships. The carangiform fishes, which include approximately 1,100 species in 29–34 families, were initially recovered as a clade in DNA-based studies. Subsequent to its initial recovery, many molecular phylogenies have been published assessing carangiform relationships, but these studies present a conflicting array of hypotheses on the intrarelationships of this clade. In addition to this diversity of hypotheses, no studies have explicitly diagnosed the clade or its major subgroups from a morphological perspective or conducted a simultaneous analysis to put forth synapomorphies for relationships across the Carangiformes using a combination of molecular and morphological data. In this study, we performed combined analyses of new and previously identified discrete morphological characters and new and previously published genome-scale data to characterize the evolutionary history and anatomical variation within this clade of fishes. Our novel morphological dataset included 201 hard and soft tissue characters, and it was combined with a novel dataset of 463 ultraconserved element loci. Our combined analysis of these data resulted in a monophyletic Carangiformes, with a series of subclades nested within. We put forth a series of subordinal names based on the recovered branching pattern, morphological character evidence, and relative stability in large-scale studies. These suborders are the Centropomoidei, which includes Centropomidae, Lactariidae, Latidae, and Sphyraenidae; Polynemoidei, which includes Polynemidae and the infraorder Pleuronectoideo; Toxotoidei, which includes Leptobramidae and Toxotidae; Nematistioidei, which includes Nematistiidae; and Menoidei, which includes Menidae and Xiphioidea. Furthermore, we highlight and discuss morphological characters that support the relationships between two or more lineages of carangiform fishes. Finally, we highlight patterns of morphological convergence among some carangiform fishes and their previously hypothesized sister lineages.

Lowland Leopard Frogs (Rana yavapaiensis) have experienced extensive population declines over the last century. In California, this species was historically known to occur in scattered localities in the extreme southeastern portion of the state, but it has not been positively documented since 1965. Subsequent to this decline in California, nonnative Rio Grande Leopard Frogs (R. berlandieri) have expanded into localities previously occupied by R. yavapaiensis. The lack of extensive formal surveys and the difficulty distinguishing between these species using morphological characters have caused uncertainty about whether Lowland Leopard Frogs persist within their historical range in California. Recently, leopard frogs that could not be confidently identified to species have been observed at historical localities of R. yavapaiensis. Thus, we undertook a formal study of these populations to characterize their morphological and genetic variation, and conclusively determine to which species they belong. Our genetic analyses demonstrate that these frogs are R. berlandieri, but the morphological characters typically used to diagnose these species are largely overlapping. Further complicating field identifications, for some morphological characters, the California R. berlandieri are more similar to R. yavapaiensis than to native-range R. berlandieri. Additionally, invasive R. berlandieri show greater variation in a key character—the condition of the inset dorsolateral folds—than that found across much of the species' native range. These results demonstrate the potential for morphological change during rapid population expansions to confound species identifications. Our findings have implications for future efforts to resolve the status of R. yavapaiensis in California and to identify other native leopard frogs found within the expanding range of R. berlandieri. Our results also highlight the utility of genetic approaches for reliably identifying morphologically similar leopard frogs.

We examined eye-bulging behavior in relation to scent-marking and chemosensory behavior in three species of iguanian lizards, Sceloporus jarrovii, S. tristichus, and S. virgatus, in a controlled environment. We studied males of the three species and also females of S. jarrovii and S. tristichus. Overall, the frequency of eye-bulging was positively correlated to the frequency of chin wipes in males, but not females. Chin wipes rarely occurred in the absence of eye-bulging; they were closely associated with the latter and, to some degree, to other chemosensory behavior. Of the three species, S. virgatus exhibited the highest eye-bulging frequency. The possibility of eye-bulging behavior being utilized for chemical communication is discussed.

Predators can affect the development, fitness, and behavior of prey species in myriad ways. In response to the threat of predation, tadpoles can alter growth rate, morphology, and foraging behavior. Changes to tadpole development have the potential to alter life history characteristics and are therefore of interest in species of conservation concern. Using experimental mesocosms, we explored how non-lethal predators affected the larval development of the Pine Barrens Treefrog, Hyla andersonii, a near-threatened species in the United States. We found that caged dragonflies (Anax junius) induced darker tail coloration and deeper tail fins in tadpoles of H. andersonii, but the dragonflies did not affect tadpole behavior, survival, or size at metamorphosis. Non-lethal predator presence also induced greater within population variation in the tail color trait compared to populations without predators. This result suggests that there may be underlying genetic variation in the ability to express phenotypically plastic traits, a concept that should be explored further because it has implications for the evolution of inducible defenses. These findings support the existence of an adaptive syndrome among hylid tadpoles, where tadpoles develop conspicuous tail morphology in response to larval dragonfly predators.

A new species of Chromis (Teleostei: Pomacentridae) is described from three specimens collected at 90 m depth in a mesophotic coral ecosystem at Rapa Nui, Chile. Chromis mamatapara, new species, can be distinguished from its congeners by the following combination of characters: dorsal-fin rays XIV,13–14; pectoral-fin rays 18–19, third from top of fin longest; tubed lateral-line scales 18; total gill rakers on first arch 30–32; vertebrae 11+15; and by coloration of living specimens, especially the presence of a single, pronounced, white spot, roughly the same diameter as the orbit, located where the posterior base of the dorsal fin intersects the caudal peduncle. The most similar DNA barcode (mitochondrial COI gene), among those available, is Chromis tingting from Japan (3.5% uncorrected divergence); however, C. mamatapara, new species, also superficially resembles other species for which sequences are unavailable for comparisons, including C. okamurai from Japan and C. struhsakeri from Hawaii. Due to the high geographic isolation and consequently high endemism in the Rapa Nui region, we believe that C. mamatapara, new species, is endemic to mesophotic ecosystems of Rapa Nui, Isla Salas y Gómez, and nearby seamounts, a discovery that contributes to the high endemism of the region and thus the need for conservation efforts.

Oviposition site selection is critical for the reproductive success of oviparous organisms. We investigated oviposition site selection in three species of glass frogs—Espadarana prosoblepon, Hyalinobatrachium valerioi, and Teratohyla spinosa—in northeastern Costa Rica. We conducted nocturnal visual encounter surveys to estimate glass frog egg mass abundance and characterize oviposition site features in streams of three different habitats (pasture, secondary forest, and mature forest). Our results show differential oviposition site selection among all three species depending on vegetation and stream features. Hyalinobatrachium valerioi and T. spinosa, which oviposit almost exclusively on the underside of leaves, selected smooth leaves, while E. prosoblepon, which oviposits on the upper side of leaves or in moss, used moss eight times more than expected on the basis of availability. Hyalinobatrachium valerioi was found on larger leaves than T. spinosa and E. prosoblepon. Teratohyla spinosa and E. prosoblepon both oviposited most frequently above slow-moving water, while H. valerioi oviposited most frequently above fast-moving water. Espadarana prosoblepon was the only species affected by habitat type and had higher abundances of egg masses in mature forest than in secondary forest and pasture. Our results suggest that microhabitat plays a larger role in oviposition site selection than larger habitat classification. We propose that appropriate riparian microhabitat is a critical factor in sustaining glass frog populations in modified habitats and highlight the importance of preserving riparian corridors in altered landscapes.

Predation can have strong effects on the structure of pond-breeding amphibian communities. Many factors can influence the outcome of predator–prey interactions, including differences in densities, identities, and body sizes of both predator and prey. These different mediating factors can impart synergistic impacts on predation rates, though distinguishing such interactions among multiple factors are underexplored. We examined whether different body sizes of two predators, larval Marbled Salamanders (Ambystoma opacum) and adult Lesser Sirens (Siren intermedia), varied in their ability to forage on larval anurans across a range of prey densities. We specifically tested whether attack rates and handling times, the two main parameters of functional response models, varied across three size classes in both predator species. We found that larval Marbled Salamanders exhibited a Type II (saturating) functional response and that larger individuals had higher attack rates and shorter handling times, resulting in greater prey mortality at higher prey densities with larger predators. In contrast, Lesser Sirens were largely ineffective predators despite being an order of magnitude larger in body size than Marbled Salamanders; tadpole mortality was largely unrelated to their own density. Predator body size was a significant predictor of prey mortality for both predator species. Overall, our study shows that species identity could be as important as predator body size when predicting the outcomes of predator–prey interactions.

A second species of Acanthobunocephalus is described from tributaries of the lower Purus River in the Amazon Basin, Brazil. Acanthobunocephalus scruggsi, new species, is distinguished from all other aspredinid species by its reduced number of fin rays: four pectoral-fin rays (vs. five or more), two dorsal-fin rays (vs. three or more, except Amaralia hypsiura), five pelvic-fin rays (vs. six), four to five anal-fin rays (vs. six or more, except Bunocephalus verrucosus), and nine caudal-fin rays (vs. 10, except Hoplomyzontinae, Amaralia, Platystacus, Bunocephalus chamaizelus, and Bunocephalus minerim). Osteological aspects of the new species of Acanthobunocephalus are described using cleared and stained specimens and high-resolution x-ray computed tomography (HRXCT), and compared with Acanthobunocephalus nicoi and other aspredinids. Generic assignment is based on putative apomorphic shared features and a morphological diagnosis for Acanthobunocephalus is presented.

Range limits can be caused by a multitude of abiotic or biotic factors, but all of these must act through the demography of range-edge populations. Woodland salamanders of the genus Plethodon often exhibit distinct range boundaries where the distributions of competing species meet. Because of their high densities and low mobility, Plethodon are well suited for studies of how fitness-related traits change as species approach their range limits. Across contact zones between the mountaintop endemic Peaks of Otter Salamander (Plethodon hubrichti) and the widespread Eastern Redback Salamander (Plethodon cinereus), we measured changes in three salamander traits: 1) body condition, 2) frequency of tail loss, and 3) proportion of hatchlings. We then used hierarchical Bayesian models to compare these traits among five site types: allopatric sites for both species, sites where one of the species was dominant and the other was rare, and mixed sites containing high densities of both species. For P. hubrichti, we found no consistent changes in body condition across contact zones. However, frequency of tail loss increased continuously from allopatric sites (21%) to rare sites (54%). We also found evidence of reduced hatchling proportions at sites outside of allopatric areas (15–16% versus 30% at allopatric sites). For P. cinereus, body condition was higher at allopatric sites compared to sites within the contact zone. Similar to P. hubrichti, frequency of tail loss in P. cinereus increased continuously from allopatric sites (27%) to sites where P. cinereus were rare (50%). However, for P. cinereus, we did not find evidence of reduced hatchling numbers towards the edge of their range margin. Overall, our results suggest that both species likely have reduced fitness as they approach their range margin. Tail loss, which may reflect interference competition, effects of predation, or interactions between these, could potentially act as a density-dependent factor that stabilizes the range boundary between these species, at least over shorter time scales.

A new species of Hyphessobrycon from a tributary of the Rio Paru do Oeste (Rio Trombetas basin), at the lower Amazon basin draining the Guiana Shield region in Pará State, Brazil, is described. The new species presents a unique combination of an irregularly-shaped humeral blotch, a broad diffuse midlateral stripe, and a roughly triangular caudal peduncle blotch. The new species is herein included in the Hyphessobrycon agulha species-group, and comparisons with species belonging to this group and to a similar-looking non-congener, Hemigrammus bellottii, are presented.

Vast differences in available resources between habitats can have profound influences on aspects of an organism's life history, such as reproductive investment. Our study investigated how differences in nutrient availability affect sperm size in Diamond-backed Watersnakes (Nerodia rhombifer). We compared body size and sperm morphometrics between two populations with differing nutrient availability: a naturally occurring lake and a commercial fish farm. We hypothesized that prey availability affects sperm morphometrics. Our null hypothesis was that there would be no significant difference in sperm morphometrics between populations, whereas our alternative hypothesis was that the snakes from the fish farm would have significantly longer sperm. We measured total sperm length, sperm head length, sperm tail length, and snout–vent length (SVL). We then used two-tailed t-tests and AIC model selection to test our hypotheses. SVL was not correlated with sperm size. Furthermore, none of the sperm morphometrics were significantly different between the two populations. Finally, a nearly 1:1 correlation between sperm tail length and total sperm length was found. AIC model selection corroborated these results by choosing only sperm head length and sperm tail length as significant predictors of total sperm length. This is the first published study to explicitly compare sperm morphometrics between two populations of the same snake species. Additional studies of this nature are required to corroborate whether lack of significant differences in sperm morphometrics among snake populations are common.

Legacies of ancient riverine systems are often manifest in patterns of genetic diversity within aquatic species. The ancient Teays River, a principal drainage of the eastern United States, engaged in several ephemeral connections with neighboring palaeodrainages prior to and during the Pleistocene, when cyclical glacial advance and retreat reconfigured the region's fluvial systems. This study assayed DNA-sequence diversity at one mitochondrial (mtDNA) and three single-copy nuclear DNA (scnDNA) loci from the Tonguetied Minnow (Exoglossum laurae), a species distributed as four disjunct populations, one each within the Upper Great Miami, Upper Allegheny, Upper Genesee, and New rivers. Mitochondrial DNA variation revealed that the New River harbors the highest diversity (h = 0.73) and that the Tonguetied Minnow is composed of two ancient lineages, a Teays River lineage and a Pittsburgh River lineage. Analyses of the scnDNA loci revealed sharing of alleles among populations of E. laurae and between the Tonguetied Minnow and its only congener, the Cutlip Minnow (E. maxillingua), sampled from the Roanoke and Potomac rivers. The probability of interspecific hybridization in the New and Upper Genesee rivers was estimated as 0.16 and 0.34, respectively, but it is likely that some degree of incomplete lineage sorting contributed to these estimates. Probabilities of interspecific hybridization for Cutlip Minnow were 0.62 and 0.65, for the Roanoke and Potomac rivers, respectively, and might reflect ancient hybridization resulting from stream capture events involving these drainages by the Teays River. Management strategies should focus on maintaining the security of the Pittsburgh River lineage in the Upper Great Miami and Upper Allegheny River drainages. Finally, insights into the Tonguetied Minnow's rather convoluted taxonomic history are few, but genetic variation is inconsistent with subspecies status for Tonguetied Minnow in the Upper Great Miami River drainage.

Analyses of morphological and molecular data from recently collected specimens of Nemacheilus from Cambodia, Malaysia, and Thailand indicate that N. pallidus is a junior synonym of N. masyae, and an undescribed species of Nemacheilus occurs in large tributaries of the Mekong River in Thailand. The new species, described herein, is small—with a maximum-known standard length of 28.6 mm—and has a distinctive color pattern of dusky black bars along the side of the body that cross over the back and join the bars on the other side. Molecular phylogenetic analyses suggest that the new species is most closely related to N. masyae, which reaches a much larger size—to 66.2 mm SL—and otherwise is easily distinguished from the new species. The new species is known from the Songkhram and Mun river drainages in Thailand and appears to be restricted to the Khorat Plateau ecoregion of the Mekong River basin. Nemacheilus masyae occurs throughout mainland southeast Asia, including in the Chao Phraya, Mae Klong, Mekong, and coastal drainages of the Malay Peninsula.

Amphibians are currently facing widespread population declines, primarily due to the introduction of anthropogenic stressors, which have the potential to alter ecosystem dynamics and elicit long-term physiological responses resulting in overall population declines. Population assessments typically rely upon genomics, demography, and geographic isolation; however, when physiological parameters are included, mechanistic explanations for population declines can be determined. Rapid population assessments that can be related to specific microhabitat characteristics for management purposes can be achieved by implementing a chronic stress proxy, such as neutrophil: lymphocyte (N:L) ratios. As a long-lived habitat specialist, facing dramatic population declines with state and federally protected populations, the Hellbender (Cryptobranchus alleganiensis) is a good candidate species for applying N:L ratios to assess population vulnerability and habitat quality. This study used N:L ratios as a proxy of chronic stress among Hellbender populations to determine environmental variables potentially correlated with chronic stress. Additionally, comparisons of N:L ratios were made among Hellbender populations to examine applicability of this method for assessing among-population differences. Of the microhabitat variables assessed, high conductivity, low pH, and low dissolved oxygen correlated with elevated N:L ratios. In addition, N:L ratios differed significantly among Hellbender populations, which suggests the utility of N:L ratios as an indicator of population-level differences. Specifically, where traditional methods lack the ability to detect concerns, physiological assessment suggested certain populations may be of concern in regard to experiencing chronic stress. Including physiological parameters in viability and vulnerability assessments more frequently, such as the one described here, can provide evidence of population concerns earlier than traditional methods, and allow for better management strategy by elucidating specific environmental variables contributing to stress.

A new species of Hypomasticus is described from the Rio de Contas, a coastal drainage of eastern Brazil, and its phylogenetic position is proposed based on molecular data. The new species is diagnosed among Anostomidae by possessing a downturned mouth with compressed teeth arranged side by side, 37 or 38 lateral-line scales, three scale series between the dorsal-fin origin and the lateral line and between the lateral line and the pelvic-fin origin, and 12 scale rows around the caudal peduncle. Mitochondrial DNA sequences provide evidence that the new species is closely related to H. mormyrops, H. thayeri, H. copelandii, and H. steindachneri, a clade of species endemic to coastal drainages of eastern Brazil. These results combined with a previous phylogeny support the reallocation of the latter two species from Leporinus to Hypomasticus. The new species is herein considered to be Endangered under the IUCN criteria, due to a small Extent of Occurrence, severely fragmented population, and continued decline of area, extent, and quality of habitat.