搜索结果：snakes

To date, cases of snake infection caused by Morganella morganii and its effects on the intestinal microecology of snakes remain poorly documented. A pathogenic strain, designated NM-11, was isolated from diseased and dead snakes collected from a snake farm in China. In this study, strain NM-11 was identified as Morganella morganii through morphological observation, physiological and biochemical characterization, 16S rRNA gene sequencing, as well as genome-based average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) analyses. Subsequently, artificial challenge assays were performed to evaluate its pathogenicity. The whole genome of the strain was sequenced using PacBio long-read technology, and antimicrobial susceptibility tests were conducted to characterize its antibiotic resistance profile. Furthermore, high-throughput sequencing was applied to explore the alterations in intestinal microbial diversity of Ptyas mucosus upon infection with strain NM-11. Pathogenicity assays revealed that strain NM-11 exhibited strong virulence. After experimental infection, Ptyas mucosus displayed typical clinical signs including depression, lethargy and diarrhea. Gross pathological examination revealed extensive hemorrhage in the abdominal cavity, lungs and gastrointestinal tract, and histopathological observation confirmed severe lesions in multiple organs. Antimicrobial susceptibility tests confirmed the strain was multidrug-resistant (MDR). It had high resistance to many antibiotics. These drugs include polymyxin B, tetracycline, cefuroxime, cephalexin, erythromycin, vancomycin and streptomycin. Intestinal microbiota analysis indicated that infection with NM-11 remarkably reshaped the intestinal microbial community structure of Ptyas mucosus and increased the overall microbial diversity, accompanied by a significant rise in the relative abundance of Morganella morganii. This is the first report of Morganella morganii isolated and identified from diseased snakes in China. Our findings clarify the pathogenic characteristics and antibiotic resistance profile of this resistant strain against Ptyas mucosus. The results provide fundamental scientific evidence for the clinical diagnosis and antimicrobial prevention and treatment of Morganella morganii infection in snakes, and also offer valuable insights for reptile medicine and public health risk prevention and control.

Animals reliant on seasonal refugia face timing challenges because refugia can act as temporal bottlenecks that limit access to vital resources including food, mates, and suitable thermal conditions. Consequently, the timing of entry into and exit from refugia carries fitness consequences, particularly for temperate migratory reptiles that must balance the threat of low winter temperatures against short active seasons. How such species coordinate migration with refugia use during thermally unpredictable fall and spring transitions remains poorly understood. One potential strategy is the use of staging periods, temporary pauses near refugia that decouple migration timing from entry into or exit from refugia, allowing individuals to synchronize seasonal transitions with favorable conditions. Although staging is well documented in other migratory taxa, it remains poorly studied in reptiles. Here, we used Timber Rattlesnakes (Crotalus horridus) to investigate the existence, timing, and function of fall and spring staging in a refugia-dependent migratory reptile. During the 2021-2022 and 2022-2023 overwintering periods, we observed prolonged fall (average in 2021 = 29 days, 2022 = 8 days) and spring (average in 2022 = 22, 2023 = 26 days) staging, during which snakes remained close to refugia, exhibited limited movement, and entered and exited refugia primarily at night. Movements were consistently associated with two thermal thresholds: on average, ingress into and egress from refugia occurred near ~14°C, whereas fall arrival and spring departure occurred near ~19°C, suggesting temperature may act as an important proximate cue. Consequently, snakes spent over 6 months within refugia, extended to nearly 8 months when staging periods were included, leaving only ~4 months for active-season activities. Our results provide evidence that prolonged staging represents distinct but phenologically flexible phases, functioning as adaptive buffers that likely help individuals navigate thermally variable seasonal transitions. Recognizing staging as a functional component of refugia use has important implications for understanding phenological risk and climate sensitivity in migratory, refugia-dependent ectotherms.

The clade of blindsnakes historically placed into Ramphotyphlops Fitzinger was divided into several genera in 2014 based on the topology of a molecular phylogeny. We examine the molecular and morphological evidence used for recognizing two of those genera (the diverse Australian Anilios Fitzinger, and the monotypic Lesser Sundan Sundatyphlops Hedges, Marion, Lipp, Marin & Vidal) and find the evidence insufficient to support their distinction. Post hoc attempts at that time to define Anilios and Sundatyphlops using morphological data relied on using among-species averages of within-species means, an arbitrary approach largely driven by pooling species on geographic grounds, which ignored tremendous ranges of overlap in all morphological features claimed to be diagnostic. Three New Guinean species were also arbitrarily assigned to Anilios in the absence of any molecular or morphological evidence. The sole subsequent molecular study that has included the type species of Ramphotyphlops showed it to be sister to but virtually indistinguishable from Anilios. Lastly, all later molecular studies involving these snakes have consistently found the few species of Ramphotyphlopssensu stricto sampled (n = 1-3) to be paraphyletic when Anilios and Sundatyphlops are recognized. Consequently, we find there is no evidentiary basis for recognizing Anilios or Sundatyphlops as valid lineages distinct from Ramphotyphlops, and continuing to do so renders the latter paraphyletic; thus, we synonymize Anilios and Sundatyphlops with Ramphotyphlops. The taxonomic muddling created by recognizing these genera has persisted because consistently poor sampling of non-Australian members of Ramphotyphlops has not allowed for well-supported clarification of relationships among those lineages.

The reed snakes of the genus Calamaria H. Boie in F. Boie are among the least-studied Southeast Asian snakes, with several taxa known only from their original description. Calamaria pavimentata annamensis Bourret, 1937, described from "Dong Tam Ve (province de Quang-tri), Annam", now Bac Huong Hoa Nature Reserve, Quang Tri Province, Vietnam, based solely on a single specimen. This taxon was subsequently treated as a junior synonym of C. pavimentata Duméril, Bibron & Duméril, for example by Smith (1943) and Inger & Marx (1965), without any comprehensive reassessment to date. Here, we report the rediscovery of this taxon based on three newly collected specimens from the type locality and revalidate it as Calamaria annamensisstat. nov., based on integrative morphological and mitochondrial DNA analyses. We established detailed morphological comparisons to specimens of C. pavimentata alleged to originate from Java Island, Indonesia (type locality), and from Guangxi Province, China (as defined by Yeung et al. 2022), and other congeners from mainland Southeast Asia. Mitochondrial DNA (cytochrome b) analysis supports the distinctiveness of Calamaria annamensisstat. nov., revealing an uncorrected p-distance of 19.4% from C. pavimentata and ranging from 16.7% (C. nebulosa Lee) to 21.5% (C. lumbricoidea Boie) when compared with other congeners. This revalidation increases the number of Calamaria species to 71, of which twelve are currently recorded from Vietnam. Our findings also underscore the urgent need for comprehensive taxonomic and molecular studies on the widely distributed Calamaria pavimentata and C. septentrionalis Boulenger species complexes in Vietnam to resolve their true diversity and distribution.

The organization and function of reptilian excurrent ducts remain poorly characterized, particularly in Neotropical snakes. We provide the first integrative morphological, histochemical, immunohistochemical, and ultrastructural analysis of the proximal post-testicular ducts of Crotalus durissus across reproductive stages. Using light, transmission electron, and confocal laser microscopy, we examined the rete testis, ductuli efferentes, ductuli epididymides, and ductus epididymis of adult males. The proximal post-testicular ducts are contained within the epididymal sheath alongside the adrenal gland. No anatomical regionalization was identified along the epididymis. The ductuli efferentes exhibited cuboidal epithelium with stereocilia-like projections, while the ductuli epididymides displayed simple columnar epithelium with abundant periodic acid-Schiff (PAS) and Bromophenol Blue (BB) positive secretory granules. The ductus epididymis consisted of pseudostratified epithelium with principal, basal, and clear cells. Confocal analyses revealed wheat germ agglutinin (WGA) in principal cells of the ductus epididymis and Concanavalin A (ConA) positive secretory granules in ductuli epididymides. Aquaporin-9 immunolabeling was detected in the epithelium of the ductus epididymis and ductuli efferentes, suggesting a role in luminal fluid regulation. Ultrastructural observations of the ductus epididymis revealed extensive rough endoplasmic reticulum, Golgi complexes, microvilli, and phagolysosomes in principal cells, supporting secretory, absorptive, and phagocytic functions. Seasonal variation was evident, with snakes in testicular activity exhibiting hypertrophy of all components analyzed. Collectively, our findings indicate that these ducts of C. durissus are functionally specialized for secretion and absorption, rather than sperm storage, thereby contributing to the establishment and regulation of a luminal microenvironment essential for sperm maturation in this seasonally reproducing viperid.

The Oberhautchen cells of reptile skin possess micro-ornamentations that are complex structures with a wide diversity. The ongoing debate regarding the origin of these structures oscillates between phylogenetic and ecological drivers. The current study also contributes to this debate by examining micro-ornamentations in seven lizards from three families, one worm lizard, and four snakes from three families that have epigeal, fossorial, saxicolous, or semi-aquatic life habits. They were compared in terms of phylogeny and life habits. Additionally, the variations in different scales of the same individual and different regions of the same scale were studied. The aim of comparing phylogenetically distant species among reptiles was to understand whether micro-ornamentation morphologies evolved convergently in species with the same life habits. The results showed that there are three cell shapes, two cell borders, five cell surfaces, and three ridges as morphological character states within the studied species. These variations might also differ significantly on different scales for an individual and even change gradually on the same scale. The ancestral form possibly has polygonal cells and regular borders with a smooth surface where the ridges are absent. It is essential to consider that convergent evolution facilitates the resolution of "problems" with similar "answers," however, comparisons suggest that phylogenetic limitations are more decisive than habitat restrictions in shaping the diversity of reptile skin micro-ornamentation.

Various aspects of movement, excavation, ecology, and muscle structure of Gymnophiona species have been reported. However, the unique mechanisms and dynamics of peristaltic locomotion and excavation are unclear, particularly for soil-inhabiting Gymnophiona spp. Previous studies primarily focused on forward locomotion and thrusting behavior, with less attention paid to the underlying vertebral and muscular mechanisms. Herein, using X-ray computed tomography, video analysis, and tissue specimens, we determined that the Mexican caecilian (Dermophis mexicanus) could generate peristaltic locomotion via coordinated bending and extension of the vertebral column and associated musculature, including the M. dorsalis trunci, M. subvertebralis, and external muscular sheath, facilitating both forward and backward movement. Thrust forces akin to a multistep spring mechanism are generated by extending their twisted and bent spines across the head, neck, chest, and abdomen. Each region flexes its vertebrae and modulates muscle size to fulfill various functions. The spinous processes of the vertebrae are loosely connected to independent segmental annuli via tendons. Unlike snakes, caecilians can move forward and backward by bending and stretching their spinal columns within their bodies, allowing movement through soil when there is space for their heads and bodies, which confers remarkable survival advantages. Dorsoventral and right-left dynamics of the spinal and muscular structures and the locomotion of Mexican caecilians was confirmed.

The mechanisms by which novel differentiation pathways evolve to produce new cell types are still not fully understood. Chromatophores, the pigmented cells in the skin, offer an ideal paradigm because each type independently develops from neural crest cells to produce a distinct colour using well-characterised biosynthetic pathways. Here we show, using single-cell gene expression analyses, that canonical chromatophores develop in the embryonic skin of corn snakes and bearded dragon lizards. Yet, we identify previously undescribed chromatophore subtypes in the bearded dragon. These populations co-express progenitor and mature markers and possibly contribute to embryonic skin patterning, as revealed by whole-mount in situ hybridisation. Comparative analyses uncover that while mature chromatophores show cross-species similarity reflecting shared pigmentary function, progenitor states differ in transcription factor usage, including species-specific deployment of MITF, PAX7, and TFEC. Integration with teleost and amphibian datasets confirms that diversification of pigmentation arises through distinct progenitor trajectories converging on similar mature states.

Although the ultrastructural characteristics of motor neurons, their myelin-forming cells, and skeletal muscle fibers are very well described in mammals, much less is known in reptiles, especially snakes. In this context, two specimens of Bothrops jararaca were euthanized for morphological analysis of the somatic motor system (SMS). Samples of the thoracic spinal cord, thoracic spinal nerves, and epaxial muscles were collected and processed for investigation by transmission electron microscopy. In the central nervous system (CNS), motor neurons and their myelin sheaths produced by oligodendrocytes presented ultrastructural characteristics similar to those previously described in mammals. Likewise, thoracic somatic nerves, their Schwann cell-derived sheaths, and the innerved skeletal fibers showed comparable features. Morphological similarities between reptilian and mammalian neural cells are probably linked to their evolutionary conservation throughout vertebrate phylogeny.

Evolutionary potential, the capacity to evolve in response to environmental change, is important for the persistence of threatened species. This potential is diminished by genetic drift in small populations, causing the loss of genetic diversity and reduced efficiency of selection. We introduce an approach to evaluate evolutionary potential that integrates across these components by conducting genome-scale selection analyses of genes of ecological importance. We inferred selection in small populations of the endangered eastern massasauga rattlesnake (Sistrurus catenatus) by comparing summary statistics between background regions and focal adaptive gene families underlying the Major Histocompatibility Complex and venom protein phenotypes. We applied tests sensitive to selection at multiple timescales to populations that have experienced differential declines and compared results with an outbred population of the sister species, S. tergeminus. We detected signatures of selection in focal regions in the recent and distant past, suggesting balancing selection as a dominant force shaping genetic diversity underlying these traits. Recently declined S. catenatus populations exhibited weaker signals of recent selection, consistent with reduced efficiency of selection when effective population size is small. Drift has reduced genome-wide genetic diversity both in relatively large and recently declined S. catenatus populations compared to outbred S. tergeminus, but these reductions were less pronounced in focal adaptive regions. These findings suggest that selection has buffered the loss of adaptive variation, but that small populations of these snakes may be approaching a critical loss of evolutionary potential limiting their capacity to respond to human-induced environmental change.

Reconstructing patterns of evolution requires understanding the interrelationships of species, yet evolutionary relationships that defy resolution and calibration in time are commonplace across the Tree of Life. Here, we investigate the dynamics of temporal and topological uncertainty by generating a phylogeny of jawed vertebrates using 1105 exonic loci sampled for 540 species spanning all major orders and most families of gnathostomes. Across loci and DNA sequence sites, we observe rapid reductions in statistical support for the monophyly of jawed vertebrate clades that originated around the Cretaceous-Paleogene mass extinction. Phylogenetic signal was scrambled to different degrees during rapid successive divergences in multiple unrelated jawed vertebrate lineages that radiated in this interval, including birds, snakes, placental mammals, and acanthomorph fishes. In addition to showing that particular events have modified phylogenetic signal across the same loci in distantly related vertebrate clades, we also demonstrate how rates of genomic evolution affect our ability to infer the timescale of vertebrate evolution. By testing how the inclusion of lineages of ray-finned fishes with very fast and slow rates of molecular evolution changes inferences of the vertebrate evolutionary timescale, we show that the deepest divergences in ray-finned fishes may be impossible to accurately infer using sequence data and calibrations from a limited fossil record. These results hint at the macroevolutionary realities underlying topological and divergence time uncertainty across evolutionary trees.

New World coralsnakes (Leptomicrurus Schmidt, 1937, Micruroides Schmidt, 1928 and Micrurus Wagler, 1824) are distributed in North, Central and South America, being divided into two monophyletic groups regarding the number of triads. The South American triad group is represented by 22 species inhabiting diverse habitats including tropical forests such as the Amazon and the Atlantic Forest, as well as open vegetation formations like the Cerrado and the Caatinga. There are many information gaps within these species regarding their distribution. Herein, we provide the potential distribution of three species occurring in the northern Brazilian Atlantic Forest, also known as the Pernambuco Endemism Center (PEC). In addition to the potential distributions, we furnished an identification key for the species. Finally, we added new data on morphological and color variation from examining 13 new individuals of Micrurus potyguara as well as an expansion of its geographic distribution. The variation of meristic characteristics refers to the number of ventral and subcaudal scales. The new record expanded the geographic distribution to about 200 Km south of João Pessoa in Paraíba State, the type locality, to Maragogi in Alagoas State. The potential distributions show that the main area of the species is under great pressure due to fragmentation and habitat loss.

The genus Dryophylax currently comprises 15 widely distributed South American species of snakes. Despite recent efforts to clarify the systematic status of the genus, several species remain taxonomically poorly defined. One example is Dryophylaxnattereri (Mikan 1820), regarded first as a junior synonym of Thamnodynastes strigilis (Thunberg 1787), and later as a junior synonym of Thamnodynastes pallidus (Linnaeus 1758). Despite several historical taxonomic studies addressing other congeners, D. nattereri has been often neglected, and no author has attempted to test species boundaries. Recently, several authors referred to this taxon as Dryophylax cf. nattereri, after it was resurrected without a proper taxonomic justification. Here, we demonstrate that D.nattereri is a valid species, based on morphological data gathered from a large series of individuals distributed throughout its known distribution. We designated a neotype for D.nattereri and provide a detailed description of the species diagnostic characters, with additional data on external morphological variation, skull osteology and hemipenial morphology.