Search

Reproductive success is the ultimate measure of individual quality; however, it is difficult to determine in free-living animals. Therefore, indirect measures that are related to reproduction are generally employed. In snakes, males typically possess longer tails than females and this sexual size dimorphism in tail length (TL) has generally been attributed to the importance of the tail in mating and reproduction. Thus, intra-sexual differences in tail length, specifically within males, were hypothesized to reflect individual quality. We used a body condition index (BCI) as a measure of quality in snakes and predicted that tail length would be correlated with BCI in males. We tested our prediction by determining BCI in the free-ranging adult male and female crowned leafnose snake (Lytorhynchus diadema), a colubrid species that inhabits mainly desert sand dunes. The relative TL was correlated positively and significantly to BCI in males (F1,131 = 11.05; r2adj = 0.07; P < 0.01) but not in females, thus supporting our prediction. This is the first time that the relationship between TL and body condition was tested in a free-ranging species. In addition, sexual size dimorphism of TL increased intra-specifically with body size, which was also found in interspecific analyses following Rensch's rule. [ABSTRACT FROM AUTHOR]

Snakes exhibit a diverse array of body shapes despite their characteristically simplified morphology. The most extreme shape changes along the precloacal axis are seen in fully aquatic sea snakes (Hydrophiinae): "microcephalic" sea snakes have tiny heads and dramatically reduced forebody girths that can be less than a third of the hindbody girth. This morphology has evolved repeatedly in sea snakes that specialize in hunting eels in burrows, but its developmental basis has not previously been examined. Here, we infer the developmental mechanisms underlying body shape changes in sea snakes by examining evolutionary patterns of changes in vertebral number and postnatal ontogenetic growth. Our results show that microcephalic species develop their characteristic shape via changes in both the embryonic and postnatal stages. Ontogenetic changes cause the hindbodies of microcephalic species to reach greater sizes relative to their forebodies in adulthood, suggesting heterochronic shifts that may be linked to homeotic effects (axial regionalization). However, microcephalic species also have greater numbers of vertebrae, especially in their forebodies, indicating that somitogenetic effects also contribute to evolutionary changes in body shape. Our findings highlight sea snakes as an excellent system for studying the development of segment number and regional identity in the snake precloacal axial skeleton. [ABSTRACT FROM AUTHOR]

The emerging picture of non‐monophyly of scolecophidian snakes is increasingly indicative that fossorial lifestyle, myrmecophagous diet, and miniaturisation are powerful drivers of morphological evolution in squamate skulls. We provide a detailed description of the skull of Xenotyphlops grandidieri, with reference to the skulls of other scolecophidian snakes. The skull, which shows dramatic ventral inflection of the snout complex, is remarkably bizarre, and the mouth opening is more ventrally oriented than in other typhlopoids. The eyes are strongly reduced, and the enlarged and rather flat anterior head shield is covered in numerous sensillae. We put forward several potential explanations for the evolution of these unusual modifications. On the other hand, Xenotyphlops shares numerous synapomorphies with other typhlopoid snakes, including the highly specialized jaw mechanism. We argue that the key differences between the jaw mechanisms of Leptotyphlopidae, Anomalepididae, and Typhlopoidea provide compelling evidence for a strong role of convergence in the evolution of the scolecophidian bauplan, and these clades therefore cannot be interpreted as representative of ancestral anatomy or ecology among snakes. [ABSTRACT FROM AUTHOR]

Predator‐based selection is ubiquitous and can be a major driver of phenotypic and life‐history evolution. However, how characteristics of individual prey species influence predation risk is unknown for many taxa. This dearth of information on what factors can drive predation risk is particularly profound for small terrestrial vertebrates. We focused our research on the rough earth snake (Haldea striatula), which is ideal for this research because they are small, abundant and subject to predation from a host of predators. We then tested for the role of sex, color morph and body size on the likelihood that a snake would experience attempted predation. This was accomplished by coupling the (1) examination of natural history specimens for evidence of predation and (2) use of clay models of rough earth snakes to test for variation in predation in a natural setting. For the natural history study, we found that scars on specimens increased in frequency with body size, but wound frequency did not differ based upon color pattern or sex. For the clay model study, we found that attack rates increased with model size. Our results suggest that predation risk increases with body size in these diminutive snakes, perhaps due to greater detection probability or different predatory assemblages for larger snakes. More broadly, our results suggest that predator‐based selection may drive smaller body size, which has implications for understanding the diversity of body size in snakes. Predator‐based selection is ubiquitous and can be a major driver of phenotypic and life‐history evolution. However, how characteristics of individual prey species influence predation risk is unknown for many taxa. We studied the rough earth snake and found that predation risk increases with body size in these diminutive snakes, perhaps due to greater detection probability or different predatory assemblages for larger snakes. [ABSTRACT FROM AUTHOR]

Natural history data are important for a better understanding of distinct aspects of snake biology, and this information in scarce on Scolecophidia. Here we focus on sexual maturity and sexual dimorphism within a population of Amerotyphlops brongersmianus from the Restinga de Jurubatiba National Park, Rio de Janeiro state, Brazil. The smallest sexually active male and female showed snout-vent length of 117.5 and 158.4 mm, respectively. Females had statistically significant larger body and head length sizes, whereas males had longer tails. Juveniles showed no sexual dimorphism for any analyzed feature. Secondary vitellogenic follicles had a more opaque, yellowish/darker aspect, being larger than 3.5 mm. We reinforce that in addition to traditional features for determining sexual maturity, morphological and histological characteristics of kidneys should be evaluated in males, as well as the morphology of the infundibulum in females. Histological data show development of seminiferous tubules and presence of spermatozoa in males, and infundibulum receptacles and uterine glands in females as a sign of sexual maturity. This type of information is essential for a more accurate description of data on sexual maturity, allowing access to information on the development of reproductive structures that are not available macroscopically., (© 2023 American Association for Anatomy.)

Many snakes are uniquely adapted to ingest large prey at infrequent intervals. Digestion of large prey is metabolically and aerobically costly, and large prey boluses can impair snake locomotion, increasing vulnerability to predation. Cessation of foraging and use of refugia with microclimates facilitating digestion are expected to be strategies employed by free‐ranging snakes to cope with the demands of digestion while minimizing risk of predation. However, empirical observations of such submergent behavior from field experiments are limited. The brown treesnake (Serpentes: Colubridae: Boiga irregularis) is a nocturnal, arboreal, colubrid snake that was accidentally introduced to the island of Guam, with ecologically and economically costly consequences. Because tools for brown treesnake damage prevention generally rely on snakes being visible or responding to lures or baits while foraging, cessation of foraging activities after feeding would complicate management. We sought to characterize differences in brown treesnake activity, movement, habitat use, and detectability following feeding of large meals (rodents 33% of the snake's unfed body mass) via radio telemetry, trapping, and visual surveys. Compared to unfed snakes, snakes in the feeding treatment group showed drastic decreases in hourly and nightly activity rates, differences in refuge height and microhabitat type, and a marked decrease in detectability by trapping and visual surveys. Depression of activity lasted approximately 5–7 days, a period that corresponds to previous studies of brown treesnake digestion and cycles of detectability. Our results indicate that management strategies for invasive brown treesnakes need to account for cycles of unavailability and underscore the importance of preventing spread of brown treesnakes to new environments where large prey are abundant and periods of cryptic behavior are likely to be frequent. Characterization of postfeeding behavior changes provides a richer understanding of snake ecology and foraging models for species that consume large prey. Many snakes exhibit remarkable physiological adaptations for ingestion of large prey; despite theoretical and laboratory‐based investigations of changes in snake behavior following ingestion of large meals, field experiments documenting such behaviors are limited. We document reduction in movement and changes in refuge site selection by invasive brown treesnakes on the island of Guam following experimental feeding of rodent mass equal to one third of the snake's body mass. These changes in postfeeding movement likely reflect evolution of behaviors favoring predator avoidance and meeting metabolic demands of digestion, and can reduce the effectiveness of invasive snake control tools based on snake foraging behavior for several days after ingesting a large meal. [ABSTRACT FROM AUTHOR]

Abstract: A snake's body represents an extreme degree of elongation with immense muscle complexity. Snakes have approximately 25 different muscles on each side of the body at each vertebra. These muscles serially repeat, overlap, interconnect, and rarely insert parallel to the vertebral column. The angled muscles mean that simple measurements of anatomical cross‐sectional area (ACSA, perpendicular to the long‐axis of the body) serve only as proxies for the primary determinant of muscle force, physiological cross‐sectional area (PCSA, area perpendicular to the muscle fibers). Here, I describe and quantify the musculature of two intraguild constrictors: kingsnakes (Lampropeltis holbrooki) and ratsnakes (Pantherophis obsoletus) whose predation performance varies considerably. Kingsnakes can produce significantly higher constriction pressures compared with ratsnakes of similar size. In both snakes, I provide qualitative descriptions, detail previously undescribed complexity, identify a new lateral muscle, and provide some of the first quantitative measures of individual muscle and whole‐body PCSA. Furthermore, I compare measurements of ACSA with measurements of PCSA. There was no significant difference in PCSA of muscles between kingsnakes and ratsnakes. There is, however, a strong relationship between ACSA and PCSA measurements. I could not identify a significant difference in musculature between kingsnakes and ratsnakes that explains their different levels of constriction performance. Unmeasured components of muscle function, such as endurance and force production, might account for differences in performance between two species with similar muscle structure. [ABSTRACT FROM AUTHOR]

Objective Assess vascular permeability of the snake spectacle to sodium fluorescein during resting and shedding phases of the ecdysis cycle. Animal studied Ball python (Python regius). Procedures The snake was anesthetized, and spectral domain optic coherence tomography was performed prior to angiographic procedures. An electronically controlled digital single-lens reflex camera with a dual-head flash equipped with filters suitable for fluorescein angiography was used to make images. Sodium fluorescein (10%) solution was administered by intracardiac injection. Angiographic images were made as fluorescein traversed the vasculature of the iris and spectacle. Individually acquired photographic frames were assessed and sequenced into pseudovideo image streams for further evaluation Conclusions Fluorescein angiograms of the snake spectacle were readily obtained. Vascular permeability varied with the phase of ecdysis. Copious leakage of fluorescein occurred during the shedding phase. This angiographic method may provide diverse opportunities to investigate vascular aspects of snake spectacle ecdysis, dysecdysis, and the integument in general. [ABSTRACT FROM AUTHOR]

Abstract: Snakes and other limbless animals continue to attract the close attention of scientists because of their unique locomotion abilities. This paper presents a novel approach to limbless movement simulation. We built our simulation framework using position‐based dynamics. We describe the body configuration of snakes using different types of distance constraints. The limbless movement is based on the formulation of a friction constraint to model the behavior of a snake's scales. In our approach, it is easy to solve collisions between objects and self‐collisions for simulated snakes. Our model includes a dynamic geometrical environment colliding with simulated animals. Detailed patterns are presented for four main types of limbless movement: serpentine, rectilinear, concertina, and sidewinding. Finally, we present the process of computing the final smooth visual mesh from the physical simulation data. This paper concludes with several simulation scenarios showing the high‐quality results of our framework for limbless movement simulation. [ABSTRACT FROM AUTHOR]

The Javelin sand boa, Eryx jaculus, is one of the erycid snakes occurring in Iran. In order to investigate sexual dimorphism in this species, 12 morphological characters were examined in 22 adult specimens (10 males and 12 females) from different localities in western Iran. Results showed that the number of sub-caudal scales, the relative tail length, and snout-vent length are different between sexes. Brief comparison of sexual dimorphism among species of Eryx was presented. [ABSTRACT FROM AUTHOR]

Background: Morphological divergences of snake retinal structure point to complex evolutionary processes and adaptations. The Colubridae family has a remarkable variety of retinal structure that can range from all-cone and all-rod to duplex (cone/rod) retinas. To explore whether nocturnal versus diurnal activity is responsible for constraints on molecular evolution and plays a role in visual opsin spectral tuning of colubrids, we carried out molecular evolution analyses of the visual opsin genes LWS, RH1 and SWS1 from 17 species and performed morphological analyses. Results: Phylogenetic reconstructions of the RH1 and LWS recovered major clades characterized by primarily diurnal or primarily nocturnal activity patterns, in contrast with the topology for SWS1, which is very similar to the species tree. We found stronger signals of purifying selection along diurnal and nocturnal lineages for RH1 and SWS1, respectively. A blue-shift of the RH1 spectral peak is associated with diurnal habits. Spectral tuning of cone opsins did not differ among diurnal and nocturnal species. Retinas of nocturnal colubrids had many rows of photoreceptor nuclei, with large numbers of rods, labeled by wheat germ agglutinin (WGA) and two types of cones: large cones sensitive to long/medium wavelengths (L/M) and small cones sensitive to ultra-violet/violet wavelengths (UV/VS). In contrast, retinas of diurnal species had only one row of photoreceptor nuclei, with four types of cones: large and double L/M cones, small UV/VS cones and a second group of small cones, labeled by WGA. Conclusions: For LWS gene, selection tests did not confirm different constraints related to activity pattern. For SWS1, stronger purifying selection in nocturnal lineages indicates divergent evolutionary pressures related to the activity pattern and the importance of the short wavelength sensitivity at low light condition. Activity pattern has a clear influence on the signatures of selection and spectral tuning of RH1, with stronger purifying selection in diurnal lineages, which indicates selective pressure to preserve rhodopsin structure and function in pure-cone retinas. We suggest that the presence of four cone types in primarily diurnal colubrids might be related to the gain of color discrimination capacity. [ABSTRACT FROM AUTHOR]

Molecular sexing is routinely used in the fields of forensic investigations, population genetics and conservation biology. However, none of the assays used so far allows non-ambiguous, quick, and cheap sex identification in snakes. Here, we designed a new multiplex PCR (two panels of triplex) sexing assay using two homologous loci on sex chromosomes (snake gametologous genes), CTNNB1Z / CTNNB1W and WACZ / WACW , and two combined female-specific CTNNB1W loci. This method was successfully tested on 81 samples from 17 caenophidian snakes, but not for 20 samples from 5 henophidian snakes, suggesting that this assay was applicable across all caenophidian snake tested. Moreover, the results of the validation study comprising sensitivity, specificity, blind test, and casework with blood spots on filter paper and shed skin as a non-invasive sample confirmed the effectiveness of this assay in the forensic perspective. The assay represents a robust, cheap, rapid, and simple method which should also prove useful in unknown bodies of carcass. This efficient assay should benefit wildlife forensic laboratories and registered breeders to conform to wildlife regulations or certification of commercial trade, and boost profits for snake-breeders and conservationist snake-breeding communities. [ABSTRACT FROM AUTHOR]

Regressive evolution of anatomical traits often corresponds with the regression of genomic loci underlying such characters. As such, studying patterns of gene loss can be instrumental in addressing questions of gene function, resolving conflicting results from anatomical studies, and understanding the evolutionary history of clades. The evolutionary origins of snakes involved the regression of a number of anatomical traits, including limbs, taste buds and the visual system, and by analyzing serpent genomes, I was able to test three hypotheses associated with the regression of these features. The first concerns two keratins that are putatively specific to claws. Both genes that encode these keratins are pseudogenized/deleted in snake genomes, providing additional evidence of claw-specificity. The second hypothesis is that snakes lack taste buds, an issue complicated by conflicting results in the literature. I found evidence that different snakes have lost one or more taste receptors, but all snakes examined retained at least one gustatory channel. The final hypothesis addressed is that the earliest snakes were adapted to a dim light niche. I found evidence of deleted and pseudogenized genes with light-associated functions in snakes, demonstrating a pattern of gene loss similar to other dim light-adapted clades. Molecular dating estimates suggest that dim light adaptation preceded the loss of limbs, providing some bearing on interpretations of the ecological origins of snakes. [ABSTRACT FROM AUTHOR]

This paper gives details of the first record of the small and poorly known dipsadine snake Atractus turikensis in Colombia. This includes the first specimens that do not correspond to the type series and the first vouchers of the species outside of Venezuela. We describe its morphology and some aspects of its natural history. [ABSTRACT FROM AUTHOR]

We used mark-recapture techniques to study the short-headed garter snake, Thamnophis brachystoma at two urban sites (Shannon Road and McClelland Park) in Erie County, Pennsylvania, USA. Mean snout-vent length (SVL) and weight was greater in females than males regardless of age class; whereas relative to total length, tail length was consistently greater in males than in females. Sex ratios did not differ significantly from 1:1 regardless of age-class. At Shannon Road, adults significantly outnumbered juveniles 3.3 to 1. While at McClelland Park, juveniles (N = 63) were nearly twice as numerous as adults (N = 31). Data regarding estimated growth are also reported. The results of the present study conform to previously published data from populations in Pennsylvania and a population near Olean, New York. [ABSTRACT FROM AUTHOR]

The thermal infrared (IR) sensing system of pit vipers is believed to complement vision and provide a substitute imaging system in dark environments. Theoretically, the IR system would best image a scene consisting of a homothermal target in cold surroundings as a bright spot on a dark background. To test this hypothesis, we evaluated how the pit viper (Gloydius brevicaudus) discriminates and strikes prey when the background temperature is either higher or lower than that of the prey (approximately 32-33°C) in different parts of the scene. Snakes were tested in a modified predation cage in which background temperatures were set to 26°C on one side and either 33 or 40°C on the opposite side when the eyes, the pit organs or neither sensory system was occluded. When the eyes were blocked, snakes preferred to strike prey on the 26°C side rather than on the 33°C side but showed no bias in the other conditions. Snakes showed no preference for 26 versus 40°C background temperature, although more missed strikes occurred when the eyes were occluded. The results thus revealed that the pit viper IR system can accomplish a 'brightness constancy' computation reflecting the difference between the target and background temperatures, much as the visual system compares the luminance of a figure and the background. Furthermore, the results show that the IR system performs less well for locating prey when the background is warmer than the target. [ABSTRACT FROM AUTHOR]

There is limited published information about disease in wild sea snakes and no standardized guideline for postmortem examination of sea snakes. Identifying causes of morbidity and mortality of marine vertebrate species has been pivotal to understanding disease factors implicated in stranding events and assisting with the formulation of conservation plans. Additionally, postmortem findings can provide valuable information on life history traits and the ecology of these reclusive species. Sick, moribund, or dead sea snakes are intermittently washed ashore along Australian and international beaches and provide an opportunity to examine a subset of the population and identify causes of population decline. We present an illustrated description of sea snake anatomy and describe a systematic approach to postmortem examination of sea snakes. We describe common pathologic conditions identified from clinical and postmortem examinations of stranded Australian sea snakes from southeast Queensland. Notable pathologic conditions include traumatic injury, inflammatory conditions, parasitic infections, and neoplasia. [ABSTRACT FROM AUTHOR]

The differentiated serous-secreting dental glands of caenophidian snakes are diverse in form despite their developmental homology. This variation makes the elucidation of their evolutionary history a complex task. In addition, some authors identify as many as ten discrete types/subtypes of ophidian oral gland. Over the past decade and a half, molecular systematics and toxinology have deepened our understanding of the evolution of these fascinating and occasionally enigmatic structures. This paper includes a comprehensive examination of ophidian oral gland structure and (where possible) function, as well as new data on rictal glands and their associated anatomy. Following this, appropriate use of terminology, especially that pertaining to homologous structures (including the controversial 'venom gland' vs 'Duvernoy's gland' debate), is considered. An interpretation of the evolutionary history of the ophidian venom system, drawing on recent results from molecular systematics, toxinology and palaeontology, concludes the paper. [ABSTRACT FROM AUTHOR]

Sonoran Desert habitat in southern Arizona is increasingly altered by urban development near metropolitan areas. Understanding how reptiles respond in these impacted habitats is critical to conservation efforts to retain intact biotic communities, especially those with a high diversity of reptile species. We surveyed snakes at one impacted site on the northern edge of the Phoenix metropolitan area in desert/urban interface, and at another site in a desert/rural interface near Florence, Arizona. The site near Phoenix was lower in species richness (15 spp.), and evenness: two snake species accounted for 75 % of all snakes encountered (total = 420). The site near Florence was higher in species richness (19 spp.), and a more even community: no species accounted for more than 20 % of snakes encountered (total = 594). Sampling methodology had a strong influence on species richness and abundance of snakes at the respective sites: road riding, coverboards, and traps each provided evidence of unique species missed by other methods. These results were compared with inventories at three other sites in the central Sonoran Desert of Arizona, and are consistent with the view that the impacted site near Phoenix is uneven, potentially as a result of a single species reacting to shifts in prey availability. [ABSTRACT FROM AUTHOR]

Background: Snakes are considered to be vomerolfaction specialists. They are members of one of the most diverse groups of vertebrates, Squamata. The vomeronasal organ and the associated structures (such as the lacrimal duct, choanal groove, lamina transversalis anterior and cupola Jacobsoni) of adult lizards and snakes have received much anatomical, histological, physiological and behavioural attention. However, only limited embryological investigation into these structures, constrained to some anatomical or cellular studies and brief surveys, has been carried out thus far. The purpose of this study was, first, to examine the embryonic development of the vomeronasal organ and the associated structures in the grass snake (Natrix natrix), using three-dimensional reconstructions based on histological studies, and, second, to compare the obtained results with those presented in known publications on other snakes and lizards. Results: Five major developmental processes were taken into consideration in this study: separation of the vomeronasal organ from the nasal cavity and its specialization, development of the mushroom body, formation of the lacrimal duct, development of the cupola Jacobsoni and its relation to the vomeronasal nerve, and specialization of the sensory epithelium. Our visualizations showed the VNO in relation to the nasal cavity, choanal groove, lacrimal duct and cupola Jacobsoni at different embryonic stages. We confirmed that the choanal groove disappears gradually, which indicates that this structure is absent in adult grass snakes. On our histological sections, we observed a gradual growth in the height of the columns of the vomeronasal sensory epithelium and widening of the spaces between them. Conclusions: The main ophidian taxa (Scolecophidia, Henophidia and Caenophidia), just like other squamate clades, seem to be evolutionarily conservative at some levels with respect to the VNO and associated structures morphology. Thus, it was possible to homologize certain embryonic levels of the anatomical and histological complexity, observed in the grass snake, with adult conditions of certain groups of Squamata. This may reflect evolutionary shift in Squamata from visually oriented predators to vomerolfaction specialists. Our descriptions offer material useful for future comparative studies of Squamata, both at their anatomical and histological levels. [ABSTRACT FROM AUTHOR]

Body composition is a measure of an animal's energetic state that can inform many research fields, yet the analysis traditionally requires individuals to be killed, and chemical analysis is labor intensive. Quantitative magnetic resonance (QMR) measures body composition noninvasively in live and nonanesthetized animals. Our aim was to validate QMR analysis for snakes by comparing it with gravimetric chemical analysis. We collected Northern Watersnakes ( Nerodia sipedon sipedon) and Eastern Massasaugas ( Sistrurus catenatus catenatus) that were found dead on roads, analyzed their body composition using the QMR scanner, and then by gravimetric chemical analysis. We compared fat mass, wet lean mass, and total water mass between the two methods, and then calculated bias, absolute error (g), and relative error (%) of the QMR analysis. Body composition values from the QMR analyses were highly correlated with the values obtained by gravimetric chemical analysis. Bias and errors were reasonable for wet lean and total water mass values, but the raw QMR data overestimated fat mass. When we calibrated the QMR using the chemical extraction data, it nearly eliminated bias and greatly reduced absolute and relative error. Therefore, following calibration, QMR analysis is an effective method to measure body composition of snakes. QMR very accurately measures wet lean and total water masses and can be used to detect changes in fat mass particularly in longitudinal studies of individuals across seasons. [ABSTRACT FROM AUTHOR]

We compared the head skeleton (skull and lower jaw) of juvenile and adult specimens of five snake species [ Anilios (= Ramphotyphlops) bicolor, Cylindrophis ruffus, Aspidites melanocephalus, Acrochordus arafurae, and Notechis scutatus] and two lizard outgroups ( Ctenophorus decresii, Varanus gilleni). All major ontogenetic changes observed were documented both qualitatively and quantitatively. Qualitative comparisons were based on high-resolution micro- CT scanning of the specimens, and detailed quantitative analyses were performed using three-dimensional geometric morphometrics. Two sets of landmarks were used, one for accurate representation of the intraspecific transformations of each skull and jaw configuration, and the other for comparison between taxa. Our results document the ontogenetic elaboration of crests and processes for muscle attachment (especially for cervical and adductor muscles); negative allometry in the braincase of all taxa; approximately isometric growth of the snout of all taxa except Varanus and Anilios (positively allometric); and positive allometry in the quadrates of the macrostomatan snakes Aspidites, Acrochordus and Notechis, but also, surprisingly, in the iguanian lizard Ctenophorus. Ontogenetic trajectories from principal component analysis provide evidence for paedomorphosis in Anilios and peramorphosis in Acrochordus. Some primitive (lizard-like) features are described for the first time in the juvenile Cylindrophis. Two distinct developmental trajectories for the achievement of the macrostomatan (large-gaped) condition in adult snakes are documented, driven either by positive allometry of supratemporal and quadrate (in pythons), or of quadrate alone (in sampled caenophidians); this is consistent with hypothesised homoplasy in this adaptive complex. Certain traits (e.g. shape of coronoid process, marginal tooth counts) are more stable throughout postnatal ontogeny than others (e.g. basisphenoid keel), with implications for their reliability as phylogenetic characters. [ABSTRACT FROM AUTHOR]

Deliberate tail loss was recorded for the first time in three large whip snakes (Dolichophis caspius) and one dice snake (Natrix tessellata). Observations were made in different years and in different locations. In all cases the tail breakage happened while snakes were being handled by researchers. Pseudoautotomy was confirmed in one large whip snake by an X-Ray photo of a broken piece of the tail, where intervertebral breakage was observed. This evidence and literature data suggest that many colubrid species share the ability for deliberate tail loss. However, without direct observation or experiment it is not possible to prove a species' ability for pseudoautotomy, as a broken tail could also be evidence of an unsuccessful predator attack, resulting in a forcefully broken distal part of the tail. [ABSTRACT FROM AUTHOR]

A new species of the Geophis dubius group is described from the mountains of the Sierra Zongolica in west-central Veracruz and the Sierra de Quimixtlán in central-east Puebla. The new species is most similar to G. duellmani and G. turbidus, which are endemic to the mountains of northern Oaxaca and the Sierra Madre Oriental of Puebla and Hidalgo, respectively. However, the new species differs from G. duellmani by the presence of postocular and supraocular scales and from G. turbidus by having a bicolor dorsum. With the description of the new species, the species number in the genus increases to 50 and to 12 in the G. dubius group. Additionally, a key to the species of the G. dubius group is provided. [ABSTRACT FROM AUTHOR]

Gravity imposes potentially important constraints on blood circulation in tall or elongate animals during upright posture or climbing. Upright postures create vertical gradients of gravitational (=hydrostatic) pressures within circulatory vessels. In terrestrial animals, this pressure potentially induces blood pooling and oedema in dependent (inferior) tissues and, secondarily, decreases blood volume reaching the head and vital organs. Arboreal snakes exhibit a suite of adaptations for countering the effects of gravity on blood circulation, including relatively non-compliant tissue compartments in the tail. However, patterns of tail length related to arboreal habitats and gravity have not been previously studied. Here, we test the hypothesis that arboreal snakes have relatively longer tails than non-climbing species, and we interpret the results within the context of adaptation to gravity stress., Length data were obtained for 226 snake species, 139 genera and 15 snake families assigned to three broad gravitational habitat categories (G-habitats: stenotopically arboreal, eurytopically arboreal/terrestrial and non-scansorial). We constructed a composite phylogenetic tree and quantified the relationships between snake morphology and G-habitat using conventional regression analysis of species data and regressions of phylogenetically independent contrasts., Mean relative tail length ( RTL) increased and mean relative snout-vent length decreased with increasing arboreality among the three G-habitats. However, mean total body length ( TL) was not different between the two arboreal G-habitats., Snakes with longer RTLs have a higher percentage of elongate blood vessels contained within the relatively non-compliant integument of the tail, which mitigates postural blood pooling experienced during climbing. TL in adult female arboreal snakes is hypothesized to be an evolutionary trade-off between demands for a longer tail to enhance cardiovascular performance and the length of body cavity to provide space for young., Our results complement previous studies correlating RTL with arboreal habitat use, in addition to physiological experiments quantifying the effects of gravity on blood flow in snakes. These results provide evidence that long RTLs of arboreal snakes function, at least in part, as an adaptive response to cardiovascular stresses on blood circulation imposed by gravity. Selection on tail length related to other factors seems less likely, but is in need of further investigation. [ABSTRACT FROM AUTHOR]

Aim Size is one of the most important and obvious traits of an organism. Both small and large sizes have adaptive advantages and disadvantages. Body size-frequency distributions of most large clades are unimodal and right skewed. Species larger than the mean or range midpoint of body sizes are relatively scarce. Theoretical models suggest evolutionary rates are higher in small organisms with short generation times. Therefore diversification rates are usually thought to be maximal at relatively small body sizes. Empirical studies of the rates of molecular evolution and clade diversification, however, have usually indicated that both are unrelated to body size. Furthermore, it has been claimed that because snakes are longer than lizards, the size-frequency distribution of all squamate species is bimodal overall. We examined the shape of the size-frequency distribution of nearly all Squamata and Rhynchocephalia species, and investigated how size affected diversification rates. Location Global. Methods We collected data on maximum body length for 9805 lepidosaur (squamates and the tuatara) species (99.7% of all species) and converted them to mass using clade-specific allometric equations. Using methods that test for relationships between continuous traits and speciation and extinction rates on a large, dated phylogeny (4155 species), we investigated the relationship between diversification rates and body size. Results Living squamates span six orders of magnitude in body size, eight when giant extinct snakes and mosasaurs are included. The body size-frequency distributions of snakes and lizards separately, and of all lepidosaur species combined, are unimodal and right skewed. Nonetheless, we find neither linear nor hump-shaped relationships between size and diversification rates, except in snakes, where speciation and diversification are hump shaped. Main conclusions Despite a clear modality and skew in the body sizes of lepidosaurs, we find little evidence for faster diversification of modal-sized taxa, perhaps implying that larger-sized clades are relatively young. [ABSTRACT FROM AUTHOR]

The discovery of three new species of Synophis snakes from the eastern slopes of the tropical Andes in Ecuador and Peru is reported. All previous records of S. bicolor from eastern Ecuador correspond to S. bogerti sp. n., which occurs between 1000-1750 m along a large part of the Amazonian slopes of the Ecuadorian Andes. In contrast, Synophis zamora sp. n. is restricted to southeastern Ecuador, including Cordillera del Cóndor, between 1543-1843 m. Synophis insulomontanus sp. n. is from the eastern slopes of the Andes in central and northern Peru, between 1122-1798 m, and represents the first record of Synophis from this country. All three new species share in common a large lateral spine at the base of the hemipenial body. A molecular phylogenetic tree based on three mitochondrial genes is presented, including samples of Diaphorolepis wagneri. Our tree strongly supports Synophis and Diaphorolepis as sister taxa, as well as monophyly of the three new species described here and S. calamitus. Inclusion of Synophis and Diaphorolepis within Dipsadinae as sister to a clade containing Imantodes, Dipsas, Ninia, Hypsiglena and Pseudoleptodeira is also supported. Resumen Se reporta el descubrimiento de tres especies nuevas de serpientes Synophis de las estribaciones orientales de los Andes tropicales en Ecuador y Perú. Todos los registros previos de S. bogerti del oriente ecuatoriano corresponden a S. bogerti sp. n., la cual ocurre entre 1000-1750 m a lo largo de gran parte de las estribaciones amazónicas de los Andes ecuatorianos. En contraste, Synophis zamora sp. n. se restringe al suroriente de Ecuador, incluyendo la Cordillera del Cóndor, entre 1543-1843 m. Synophis insulomontanus sp. n. es de las estribaciones orientales de los Andes del centro y norte del Perú, entre 1122-1798 m, y representa el primer registro de Synophis para este país. Todas las tres especies nuevas comparten en común una espina lateral larga en la base del cuerpo del hemipene. Un árbol molecular filogenético, basado en tres genes mitocondriales es presentado, incluyendo muestras de Diaphorolepis wagneri. Nuestro árbol apoya fuertemente a Synophis y Diaphorolepis como taxa hermanos, así como la monofilia de las tres especies descritas y de S. calamitus. La inclusión de Synophis y Diaphorolepis dentro de Dipsadinae, como hermanas a un clado que contiene a Imantodes, Dipsas, Ninia, Hypsiglena y Pseudoleptodeira también es apoyada. [ABSTRACT FROM AUTHOR]

The article discusses the fossil snake Tetrapodophis amplectus with four legs of the Early Cretaceous period of (Aptian) Crato Formation in the Gondwana contintent, present day Brazil. An overview of the evolution of the aforementioned snake, including in regard to their evolution from lizards and its aquatic adaptations and short neural spine, is provided.

Hox genes regulate regionalization of the axial skeleton in vertebrates, and changes in their expression have been proposed to be a fundamental mechanism driving the evolution of new body forms. The origin of the snake-like body form, with its deregionalized pre-cloacal axial skeleton, has been explained as either homogenization of Hox gene expression domains, or retention of standard vertebrate Hox domains with alteration of downstream expression that suppresses development of distinct regions. Both models assume a highly regionalized ancestor, but the extent of deregionalization of the primaxial domain (vertebrae, dorsal ribs) of the skeleton in snake-like body forms has never been analysed. Here we combine geometric morphometrics and maximum-likelihood analysis to show that the pre-cloacal primaxial domain of elongate, limb-reduced lizards and snakes is not deregionalized compared with limbed taxa, and that the phylogenetic structure of primaxial morphology in reptiles does not support a loss of regionalization in the evolution of snakes. We demonstrate that morphometric regional boundaries correspond to mapped gene expression domains in snakes, suggesting that their primaxial domain is patterned by a normally functional Hox code. Comparison of primaxial osteology in fossil and modern amniotes with Hox gene distributions within Amniota indicates that a functional, sequentially expressed Hox code patterned a subtle morphological gradient along the anterior-posterior axis in stem members of amniote clades and extant lizards, including snakes. The highly regionalized skeletons of extant archosaurs and mammals result from independent evolution in the Hox code and do not represent ancestral conditions for clades with snake-like body forms. The developmental origin of snakes is best explained by decoupling of the primaxial and abaxial domains and by increases in somite number, not by changes in the function of primaxial Hox genes. [ABSTRACT FROM AUTHOR]

Background: The study of craniofacial development is important in understanding the ontogenetic processes behind morphological diversity. A complete morphological description of the embryonic skull development of the Egyptian cobra, Naja h. haje, is lacking and there has been little comparative discussion of skull development either among elapid snakes or between them and other snakes. Methodology/Principal Findings: We present a description of skull development through a full sequence of developmental stages of the Egyptian cobra, and compare it to other snakes. Associated soft tissues of the head are noted where relevant. The first visible ossification centres are in the supratemporal, prearticular and surangular, with slight ossification visible in parts of the maxilla, prefrontal, and dentary. Epiotic centres of ossification are present in the supraoccipital, and the body of the supraoccipital forms from the tectum posterior not the tectum synoticum. The venom glands are visible as distinct bodies as early at stage 5 and enlarge later to extend from the otic capsule to the maxilla level with the anterior margin of the eye. The gland becomes more prominent shortly before hatching, concomitant with the development of the fangs. The tongue shows incipient forking at stage 5, and becomes fully bifid at stage 6. Conclusions/Significance: We present the first detailed staging series of cranial development for the Egyptian cobra, Naja h. haje. This is one of the first studies since the classical works of G. de Beer and W. Parker that provides a detailed description of cranial development in an advanced snake species. It allows us to correct errors and misinterpretations in previous accounts which were based on a small sample of specimens of uncertain age. Our results highlight potentially significant variation in supraoccipital formation among squamates and the need for further research in this area. [ABSTRACT FROM AUTHOR]

Objective To describe using spectral domain optical coherence tomography ( SD- OCT), digital slit-lamp biomicroscopy, and external photography, changes in the ophidian cuticle, spectacle, and cornea during ecdysis. Animals Studied Four normal royal pythons ( Python regius). Procedures Snakes were assessed once daily throughout a complete shed cycle using nasal, axial, and temporal SD- OCT images, digital slit-lamp biomicroscopy, and external photography. Results Spectral domain optical coherence tomography ( SD- OCT) images reliably showed the spectacular cuticle and stroma, subcuticular space ( SCS), cornea, anterior chamber, iris, and Schlemm's canal. When visible, the subspectacular space ( SSS) was more distended peripherally than axially. Ocular surface changes throughout ecdysis were relatively conserved among snakes at all three regions imaged. From baseline (7 days following completion of a full cycle), the spectacle gradually thickened before separating into superficial cuticular and deep, hyper-reflective stromal components, thereby creating the SCS. During spectacular separation, the stroma regained original reflectivity, and multiple hyper-reflective foci (likely fragments from the cuticular-stromal interface) were noted within the SCS. The cornea was relatively unchanged in character or thickness throughout all stages of ecdysis. Slit-lamp images did not permit observation of these changes. Conclusions Spectral domain optical coherence tomography ( SD- OCT) provided excellent high-resolution images of the snake anterior segment, and especially the cuticle, spectacle, and cornea of manually restrained normal snakes at all stages of ecdysis and warrants investigation in snakes with anterior segment disease. The peripheral spectacle may be the preferred entry point for diagnostic or therapeutic injections into the SSS and for initiating spectacular surgery. [ABSTRACT FROM AUTHOR]

Objective To describe the lacrimal system of snakes using contrast micro-computed tomography (micro- CT) with 3-dimensional reconstruction, fluorescein passage ('Jones') testing, histology, and gross dissection. Animals studied One royal python and 19 snake cadavers representing 10 species. Procedures Direct observation following injection of fluorescein into the subspectacular space, micro- CT following injection of three contrast agents into the subspectacular space, gross dissection following injection of latex into the subspectacular space, and histopathology. Results Injection of fluorescein confirmed patency, but not course of the lacrimal duct. Barium enabled clear visualization of the lacrimal duct, whereas two iodinated contrast agents proved inadequate. Collectively, micro- CT, anatomic dissections, and histology suggest tears are produced by a single, large, serous, retrobulbar gland, released into the subspectacular space via several ductules, and drained through a single punctum originating in the ventronasal subspectacular space, and the lacrimal duct, which takes one of three routes of variable tortuosity before opening into the oral cavity in close association with the opening of the duct of the vomeronasal organ. Conclusions The ophidian lacrimal duct has a generally tortuous course, and the details of its anatomy are species-variable. The tortuous course of the duct likely predisposes snakes to duct occlusion and must be considered when planning medical and surgical interventions in snakes with pseudobuphthalmos and subspectacular abscessation. [ABSTRACT FROM AUTHOR]

Snakes possess a derived anatomy, characterized by limb reduction and reorganization of the skull and internal organs. To understand the origin of snakes from an ontogenetic point of view, we conducted comprehensive investigations on the timing of skeletal elements, based on published and new data, and reconstructed the evolution of the ossification sequence among squamates. We included for the first time Varanus, a critical taxon in phylogenetic context. There is comprehensive delay in the onset of ossification of most skeletal elements in snakes when compared to reference developmental events through evolution. We hypothesize that progressing deceleration accompanied limb reduction and reorganization of the snake skull. Molecular and morphological studies have suggested close relationship of snakes to either amphisbaenians, scincids, geckos, iguanids, or varanids. Likewise, alternative hypotheses on habitat for stem snakes have been postulated. Our comprehensive heterochrony analyses detected developmental shifts in ossification for each hypothesis of snake origin. Moreover, we show that reconstruction of ancestral developmental sequences is a valuable tool to understand ontogenetic mechanisms associated with major evolutionary changes and test homology hypotheses. The 'supratemporal' of snakes could be homolog to squamosal of other squamates, which starts ossification early to become relatively large in snakes. [ABSTRACT FROM AUTHOR]

The monotypic Mimophis mahfalensis is an opisthoglyphous snake endemic of Madagascar. The goal of this study is to clarify the presence of toxin-secreting oral glands through a multidisciplinary approach. We thus provide data on the internal anatomy of the head of M. mahfalensis' and demonstrate the presence of Duvernoy's glands. Furthermore, we refer to two cases of human bitten by this species and compared this with the reported case of mild envenomation mentioned by Domergue (Arch Inst Pasteur Madagascar 56(1):299-311, ). Symptoms included brief slight local pain and minor bleeding. [ABSTRACT FROM AUTHOR]

Novel ventrally positioned extra-cloacal glands were discovered through examination of cloacal histology of female thamnophiine snakes. The glands discovered, termed ventral urodeal glands, are paired and empty into the caudal extremity of the urodeum, lateral to the opening of the urodeal sphincter, through primary ducts that resemble folds of the urodeal wall. In concordance with historical literature, these glands are the first cloacal glands described in snakes that definitively empty into the urodeum from a ventral position. Ventral urodeal glands are complex, with multiple branching ducts that empty the terminal alveolar glands. The epithelial linings of the branching duct networks are stratified (primary and secondary ducts), pseudostratified (tertiary ducts), or simple (quaternary ducts and terminal alveoli). The epithelia of the terminal alveoli stain weakly with hematoxylin, and an eosinophilic secretory material is common in the lumina of alveoli. The secretion produced in the alveoli stains positive with the periodic acid-Schiff's procedure, negative with brilliant blue, and positive with fast green, indicating that the majority of the secretion is composed of a neutral carbohydrate moiety with a minor protein component. Ventral urodeal glands were observed in all taxa of Nerodia examined, except N. cyclopion, and were not observed in any other taxa of Thamnophiini. Through optimization to Thamnophiini topologies, ventral urodeal glands either evolved once on the branch leading to Nerodia and were subsequently lost on the branch leading to N. cyclopion, or they evolved independently on the branches leading to N. floridana and all other species of Nerodia. Like many of the cloacal glands in squamates, the function of ventral urodeal glands is unknown, and further investigation is needed to elucidate the function of the secretions of these glands. [ABSTRACT FROM AUTHOR]

The evolution of arboreality in snakes is accompanied by modifications that are remarkably similar across species. Gravity is one of the most important selective agents, and arboreal snakes present adaptations to circumvent the gradient of pressure, including modifications on heart position ( HP) and body slenderness ( BS). However, the degree to which different life-history traits influence the cardiovascular system of snakes remains unclear. Here, we used an ecological and a phylogenetic approach to explore the relationship between habitat, HP, BS, and heart size ( HS) in five species of the neotropical whipsnakes genus Chironius that occupy terrestrial, semiarboreal, and arboreal habits. Our ecological comparison indicated that the arboreal species have the most posterior-positioned heart, the most slender body, and the smallest HS, whereas the terrestrial representative of the group exhibited the most anterior heart, the less flattened body, and the largest HS. After removing the phylogenetic effect, we found no difference in HP and BS between terrestrial and arboreal species. Habitat only differed when contrasting with HS. Body slenderness and HS were correlated with HP. Our results suggest that different restrictions, such as anatomical constraints, behavior, and phylogenetic inertia, may be important for the studied species. [ABSTRACT FROM AUTHOR]

Immunolocalization of glycine-rich and cysteine-glycine-medium-rich beta-proteins (Beta-keratins) in snake epidermis indicates a different distribution between beta- and alpha-layers. Acta Zoologica, Stockholm. The epidermis of snakes consists of hard beta-keratin layers alternated with softer and pliable alpha-keratin layers. Using Western blot, light and ultrastructural immunolocalization, we have analyzed the distribution of two specific beta-proteins (formerly beta-keratins) in the epidermis of snakes. The study indicates that the antibody HgG5, recognizing glycine-rich beta-proteins of 12-15 kDa, is poorly or not reactive with the beta-layer of snake epidermis. This suggests that glycine-rich proteins similar to those present in lizards are altered during maturation of the beta-layer. Conversely, a glycine-cysteine-medium-rich beta-protein (HgGC10) of 10-12 kDa is present in beta- and alpha-layers, but it is reduced or disappears in precorneous and suprabasal cells destined to give rise to beta- and alpha-cells. Together with the previous studies on reptilian epidermis, the present results suggest that beta-proteins rich in glycine mainly accumulate on a scaffold of alpha-keratin producing a resistant and hydrophobic beta-layer. Conversely, beta-proteins lower in glycine but higher in cysteine accumulate on alpha-keratin filaments present in beta- and alpha-layers producing resistant but more pliable layers. [ABSTRACT FROM AUTHOR]

The facial pits of rattlesnakes, copperheads, lanceheads, bushmasters and other American and Asian pitvipers (Crotalinae) are highly innervated and densely vascularized infrared (IR) receptor organs. For over a century, studies have focused on a small sample of model species from North America and Asia. Based on an expanded survey of Central and South American crotalines, we report a conspicuous accessory structure composed of well-defined papillae that project from the anterior orbital adnexa. The papillae are continuous with the inner chamber of the IR receptor organ and our histological and ultrastructural data suggest that they possess a well-developed nervous network and extensive vascularization; however, they lack the characteristic IR-sensitive terminal nerve masses found in the IR-receptive pit membrane. The function of the IR receptor organ papillae is unknown. [ABSTRACT FROM AUTHOR]

We develop a model to study the locomotion of snakes on inclined planes. We determine numerically which snake motions are optimal for two retrograde traveling-wave body shapes, triangular and sinusoidal waves, across a wide range of frictional parameters and incline angles. In the regime of large transverse friction coefficients, we find power-law scalings for the optimal wave amplitudes and corresponding costs of locomotion. We give an asymptotic analysis to show that the optimal snake motions are traveling waves with amplitudes given by the same scaling laws found in the numerics. [ABSTRACT FROM AUTHOR]

Abstract: A population of dice snakes (Natrix tessellata) monitored since 2008 in a small island (18ha, 850m a.s.l., FYR of Macedonia) revealed unforeseen patterns for snakes living in temperate climates. More than 5000 individuals have been marked and the density is one of the highest ever recorded (>500 resident snakes per hectare). Reproductive and mortality rates are elevated, suggesting a high population turnover. These traits evoke a tropical rather than a temperate-climate ophidian demographic system. The population is highly polymorphic, three colour morphs (dotted, grey, and black) are observed in both sexes and each morph is represented by large numbers of individuals. This polymorphism pattern was not previously documented in snakes. Data obtained for other life history traits (e.g. body size, size at maturity, clutch size, diet, predation) markedly diverged in comparison to available information. Overall, our results reinforce the notion that the strong inter-population variability (often mediated by phenotypic plasticity) of snakes should be taken into account over large geographic scales; otherwise attempts to derive general patterns may well be strongly biased. [Copyright &y& Elsevier]

Abstract: In recent years, developmental anatomy received increasing interest as a potential new source for phylogenetic research. For skeletal development, studies mainly rely on the first appearance of ossification centers. However, informative events occur during the whole course of skeletogenesis; interactions between external and internal development occur and morphometric changes take place – all of which present potential sources for phylogenetic analyses. Therefore, the Standard Event System (SES) was used to traceably describe the external development of the snake species Bothropoides jararaca and external measurements were analyzed. We then applied micro-computed tomography (μCT), clearing and double-staining, and 2D and 3D morphometric methods to describe, illustrate, and analyze the development of the head in great detail. We found a 3D flattening of the skull during ontogeny, a pattern that is not reflected in external development. This may be explained by a different relationship of skeletogenesis and external characters to the developing jaw musculature or simply by the different type of data. Clearing and double-staining and μCT-scanning revealed a broadly similar sequence in the onset of ossification. Minute differences may be due to the treatment of embryos. Bones of the dermatocranium are among the first to ossify and the development of the calcified endolymph may reflect its function as a calcium source during development. The value of phylogenetic observations using the sequence of first ossifications is critically discussed. The related heterochronic changes are interpreted to contribute at least to the very first phase of divagating skull formation among taxa. [Copyright &y& Elsevier]

ABSTRACT—The fossil snakeNajash rionegrina, from the Cenomanian–Turonian (Upper Cretaceous) of Argentina, is reinterpreted after examination of the type and referred material. The current diagnosis is emended in the light of important considerations that cast doubt on the attribution of type and referred specimens (a braincase, a quadrate, and two dentary/lower jaw fragments) used to systematize this taxon. Alternative interpretations of the anatomy of the sacrum and hind limbs are proposed. Following the reevaluation of the anatomy of the type specimen and the removal from this taxon of the above-mentioned referred material, the phylogenetic position ofN. rionegrinawas tested in a series of maximum parsimony analyses that included all groups of extant snakes, all best-known fossil snakes (i.e.,Pachyrhachis,Haasiophis,Eupodophis, Madtsoiidae, andDinilysia), and alternative outgroups. Regardless of the outgroup used to polarize the character-state transformations, our phylogenetic analyses found no support for the hypothesis thatNajash rionegrinaoccupies a position as the most basal snake. Depending on the outgroup,Najashis placed (1) in a position basal to all living snakes, but more derived than other fossil forms (most notablyPachyrhachis,Eupodophis, andHaasiophis); or (2) as the most basal representative of a clade of fossil snakes that is the sister group of living snakes; or (3) as the most basal representative of a clade of fossil snakes that is located between the Scolecophidia and the Alethinophidia. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free atwww.tandfonline.com/UJVP [ABSTRACT FROM AUTHOR]