Intestinal upregulation and specific dynamic action in snakes - Implications for the 'pay before pumping' hypothesis.

Animals which feed infrequently and on large prey, like many snake species, are characterized by a high magnitude of gut upregulation upon ingesting a meal. The intensity of intestinal upregulation was hypothesized to be proportional to the time and energy required for food processing (Specific-Dynamic-Action; SDA); hence, a positive correlation between the scope of intestinal growth and SDA response can be deduced. Such a correlation would support the so far not well established link between the intestinal and metabolic consequences of digestion. In this study I tested this prediction using an interspecific dataset on snakes gleaned from published sources. I found that SDAduration and SDAscope were positively correlated with post-feeding factorial increase in small intestine mass, but not with microvillar elongation. This indicates that a wide range of whole intestine remodelling (up- but potentially also downregulation) may temporarily prolong meal processing and that a greater magnitude of intestinal growth requires a stronger metabolic elevation. However, these effects do not seem large enough to drive the variation in the entire energetic costs of digestion, because SDAexpenditure was not affected either by intestinal or microvillar growth. I therefore propose that intestinal upregulation elicits non-negligible costs, but that these costs are a fairly small component of the whole SDAexpenditure.

Sex-specific growth is mirrored in feeding rate but not moulting frequency in a sexually dimorphic snake.

Sexual size dimorphism (SSD), commonly observed in snakes, may arise from a different growth rate between the sexes. This indicates a sex-specific resource intake that is in fact observable in free-living snakes. It is not so well known whether the sexes can express differential feeding rates under conditions unconstrained by spatial accessibility, competition, etc. Here, I studied sex-specific variation in growth, its correlate-moulting frequency, and feeding rate in a captive group of sexually dimorphic banded water snakes (Nerodia fasciata) with access to food unconstrained by predation, competition or space. I showed that the sexes did indeed differ in relative mass growth in that females grew faster than males (p = 0.02), but such differences were not apparent in the moulting rate (p = 0.19). Such differential growth was mirrored in the sex-specific feeding rate, with females ingesting a larger number of meals than males (p = 0.004). Such variation in feeding rate may be governed by an individual's energy expenditure and can be interpreted as a behavioural tendency that contributes to SSD development, independently of other behavioural characteristics. Sex-specific resource demands may drive the differential effects of increasing resource scarcity on both sexes.

Cross-Species BAC Mapping Highlights Conservation of Chromosome Synteny across Dragon Lizards (Squamata: Agamidae).

Dragon lizards (Squamata: Agamidae) comprise about 520 species in six subfamilies distributed across Asia, Australasia and Africa. Only five species are known to have sex chromosomes. All of them possess ZZ/ZW sex chromosomes, which are microchromosomes in four species from the subfamily Amphibolurinae, but much larger in Phrynocephalus vlangalii from the subfamily Agaminae. In most previous studies of these sex chromosomes, the focus has been on Australian species from the subfamily Amphibolurinae, but only the sex chromosomes of the Australian central bearded dragon (Pogona vitticeps) are well-characterized cytogenetically. To determine the level of synteny of the sex chromosomes of P. vitticeps across agamid subfamilies, we performed cross-species two-colour FISH using two bacterial artificial chromosome (BAC) clones from the pseudo-autosomal regions of P. vitticeps. We mapped these two BACs across representative species from all six subfamilies as well as two species of chameleons, the sister group to agamids. We found that one of these BAC sequences is conserved in macrochromosomes and the other in microchromosomes across the agamid lineages. However, within the Amphibolurinae, there is evidence of multiple chromosomal rearrangements with one of the BACs mapping to the second-largest chromosome pair and to the microchromosomes in multiple species including the sex chromosomes of P. vitticeps. Intriguingly, no hybridization signal was observed in chameleons for either of these BACs, suggesting a likely agamid origin of these sequences. Our study shows lineage-specific evolution of sequences/syntenic blocks and successive rearrangements and reveals a complex history of sequences leading to their association with important biological processes such as the evolution of sex chromosomes and sex determination.

Combining genetic and demographic monitoring better informs conservation of an endangered urban snake.

Conversion and fragmentation of wildlife habitat often leads to smaller and isolated populations and can reduce a species' ability to disperse across the landscape. As a consequence, genetic drift can quickly lower genetic variation and increase vulnerability to extirpation. For species of conservation concern, quantification of population size and connectivity can clarify the influence of genetic drift in local populations and provides important information for conservation management and recovery strategies. Here, we used genome-wide single nucleotide polymorphism (SNP) data and capture-mark-recapture methods to evaluate the genetic diversity and demography within seven focal sites of the endangered San Francisco gartersnake (Thamnophis sirtalis tetrataenia), a species affected by alteration and isolation of wetland habitats throughout its distribution. The primary goals were to determine the population structure and degree of genetic isolation among T. s. tetrataenia populations and estimate effective size and population abundance within sites to better understand the present and future importance of genetic drift. We also used temporally sampled datasets to examine the magnitude of genetic change over time. We found moderate population genetic structure throughout the San Francisco Peninsula that partitions sites into northern and southern regional clusters. Point estimates of both effective size and population abundance were generally small (≤ 100) for a majority of the sites, and estimates were particularly low in the northern populations. Genetic analyses of temporal datasets indicated an increase in genetic differentiation, especially for the most geographically isolated sites, and decreased genetic diversity over time in at least one site (Pacifica). Our results suggest that drift-mediated processes as a function of small population size and reduced connectivity from neighboring populations may decrease diversity and increase differentiation. Improving genetic diversity and connectivity among T. s. tetrataenia populations could promote persistence of this endangered snake.

Snake Venom Gland Organoids.

Wnt dependency and Lgr5 expression define multiple mammalian epithelial stem cell types. Under defined growth factor conditions, such adult stem cells (ASCs) grow as 3D organoids that recapitulate essential features of the pertinent epithelium. Here, we establish long-term expanding venom gland organoids from several snake species. The newly assembled transcriptome of the Cape coral snake reveals that organoids express high levels of toxin transcripts. Single-cell RNA sequencing of both organoids and primary tissue identifies distinct venom-expressing cell types as well as proliferative cells expressing homologs of known mammalian stem cell markers. A hard-wired regional heterogeneity in the expression of individual venom components is maintained in organoid cultures. Harvested venom peptides reflect crude venom composition and display biological activity. This study extends organoid technology to reptilian tissues and describes an experimentally tractable model system representing the snake venom gland.

Multi-species comparisons of snakes identify coordinated signalling networks underlying post-feeding intestinal regeneration.

Several snake species that feed infrequently in nature have evolved the ability to massively upregulate intestinal form and function with each meal. While fasting, these snakes downregulate intestinal form and function, and upon feeding restore intestinal structure and function through major increases in cell growth and proliferation, metabolism and upregulation of digestive function. Previous studies have identified changes in gene expression that underlie this regenerative growth of the python intestine, but the unique features that differentiate this extreme regenerative growth from non-regenerative post-feeding responses exhibited by snakes that feed more frequently remain unclear. Here, we leveraged variation in regenerative capacity across three snake species-two distantly related lineages ( Crotalus and Python) that experience regenerative growth, and one ( Nerodia) that does not-to infer molecular mechanisms underlying intestinal regeneration using transcriptomic and proteomic approaches. Using a comparative approach, we identify a suite of growth, stress response and DNA damage response signalling pathways with inferred activity specifically in regenerating species, and propose a hypothesis model of interactivity between these pathways that may drive regenerative intestinal growth in snakes.

Evolutionary Insights of the ZW Sex Chromosomesin Snakes: A New Chapter Added by the AmazonianPuffing Snakes of the Genus Spilotes.

Amazonian puffing snakes (Spilotes; Colubridae) are snakes widely distributed in the Neotropical region. However, chromosomal data are scarce in this group and, when available, are only limited to karyotype description using conventional staining. In this paper, we focused on the process of karyotype evolution and trends for sex chromosomes in two Amazonian Puffer Snakes (S.pulllatus and S.sulphureus). We performed an extensive karyotype characterization using conventional and molecular cytogenetic approaches. The karyotype of S.sulphureus (presented here for the first time) exhibits a 2n = 36, similar to that previously described in S.pullatus. Both species have highly differentiated ZZ/ZW sex chromosomes, where the W chromosome is highly heterochromatic in S.pullatus but euchromatic in S.sulphureus. Both W chromosomes are homologous between these species as revealed by cross-species comparative genomic hybridization, even with heterogeneous distributions of several repetitive sequences across their genomes, including on the Z and on the W chromosomes. Our study provides evidence that W chromosomes in these two species have shared ancestry.

Genomic and transcriptomic investigations of the evolutionary transition from oviparity to viviparity.

Viviparous (live-bearing) vertebrates have evolved repeatedly within otherwise oviparous (egg-laying) clades. Over two-thirds of these changes in vertebrate reproductive parity mode happened in squamate reptiles, where the transition has happened between 98 and 129 times. The transition from oviparity to viviparity requires numerous physiological, morphological, and immunological changes to the female reproductive tract, including eggshell reduction, delayed oviposition, placental development for supply of water and nutrition to the embryo by the mother, enhanced gas exchange, and suppression of maternal immune rejection of the embryo. We performed genomic and transcriptomic analyses of a closely related oviparous-viviparous pair of lizards (Phrynocephalus przewalskii and Phrynocephalus vlangalii) to examine these transitions. Expression patterns of maternal oviduct through reproductive development of the egg and embryo differ markedly between the two species. We found changes in expression patterns of appropriate genes that account for each of the major aspects of the oviparity to viviparity transition. In addition, we compared the gene sequences in transcriptomes of four oviparous-viviparous pairs of lizards in different genera (Phrynocephalus, Eremias, Scincella, and Sphenomorphus) to look for possible gene convergence at the sequence level. We discovered low levels of convergence in both amino acid replacement and evolutionary rate shift. This suggests that most of the changes that produce the oviparity-viviparity transition are changes in gene expression, so occasional reversals to oviparity from viviparity may not be as difficult to achieve as has been previously suggested.

A mid-Cretaceous embryonic-to-neonate snake in amber from Myanmar.

We present the first known fossilized snake embryo/neonate preserved in early Late Cretaceous (Early Cenomanian) amber from Myanmar, which at the time, was an island arc including terranes from Austral Gondwana. This unique and very tiny snake fossil is an articulated postcranial skeleton, which includes posterior precloacal, cloacal, and caudal vertebrae, and details of squamation and body shape; a second specimen preserves a fragment of shed skin interpreted as a snake. Important details of skeletal ontogeny, including the stage at which snake zygosphene-zygantral joints began to form along with the neural arch lamina, are preserved. The vertebrae show similarities to those of fossil Gondwanan snakes, suggesting a dispersal route of Gondwanan faunas to Laurasia. Finally, the new species is the first Mesozoic snake to be found in a forested environment, indicating greater ecological diversity among early snakes than previously thought.

Evolution of extreme ontogenetic allometric diversity and heterochrony in pythons, a clade of giant and dwarf snakes.

Ontogenetic allometry, how species change with size through their lives, and heterochony, a decoupling between shape, size, and age, are major contributors to biological diversity. However, macroevolutionary allometric and heterochronic trends remain poorly understood because previous studies have focused on small groups of closely related species. Here, we focus on testing hypotheses about the evolution of allometry and how allometry and heterochrony drive morphological diversification at the level of an entire species-rich and diverse clade. Pythons are a useful system due to their remarkably diverse and well-adapted phenotypes and extreme size disparity. We collected detailed phenotype data on 40 of the 44 species of python from 1191 specimens. We used a suite of analyses to test for shifts in allometric trajectories that modify morphological diversity. Heterochrony is the main driver of initial divergence within python clades, and shifts in the slopes of allometric trajectories make exploration of novel phenotypes possible later in divergence history. We found that allometric coefficients are highly evolvable and there is an association between ontogenetic allometry and ecology, suggesting that allometry is both labile and adaptive rather than a constraint on possible phenotypes.

Ontogenetic shifts in the diet of plains hog-nosed snakes (Heterodon nasicus) revealed by stable isotope analysis.

Wild snake diets are difficult to study using traditional methods, but stable isotopes offer several advantages, including integrating dietary information over time, providing data from individuals that have not fed recently, and avoiding bias towards slowly-digesting prey items. We used stable isotope signatures of carbon and nitrogen from scale tissue, red blood cells, and blood plasma to assess the diet of wild plains hog-nosed snakes (Heterodon nasicus) in Illinois. We developed Bayesian mixing models which, taken together, predicted that H. nasicus shifted from a juvenile diet predominantly (31-63%) composed of six-lined racerunners (Aspidoscelis sexlineatus) and their eggs to an adult diet predominantly (44-56%) composed of eggs of the aquatic turtles Chrysemys picta and Chelydra serpentina, with a contribution from toads (Anaxyrus sp.; 6-27%) during their adolescent years. These results agreed with sparse data from gut contents. Combining traditional and isotopic techniques for studying the diets of wild snakes can increase the utility of both types of data.

Recharacterization of Rhinophis dorsimaculatus Deraniyagala, 1941 (Serpentes: Uropeltidae), including description of new material.

The Sri Lankan uropeltid (shieldtail) snake Rhinophis dorsimaculatus Deraniyagala, 1941 was described originally from two specimens that were subsequently lost. The small amount of previously published data and lack of published colour photographs made this one of South Asia's most poorly known snake species, and this resulted in at least one instance of taxonomic misidentification. An additional 10 specimens from a historical collection from the vicinity of the type locality recently came to light. This material is reviewed and documented and the species recharacterized. An additional locality for the species is reported. The newly reported material helps to corroborate the taxonomic validity and distinctiveness of Rhinophis dorsimaculatus. The species is readily distinguished from congeners by having 227 or more ventral scales; a large, dorsally carinate rostral shield; posterior margins of paired anals that are largely separated by the posteriormost ventral scale; and a distinctive colour pattern with bilaterally asymmetrical dark blotches within a broad, pale middorsal stripe and regularly punctate flanks.

Venomous snakebites in children in southern Croatia.

This retrospective study represents observation of 160 children and adolescents aged up to 18 years that experienced venomous snakebites in southern Croatia and were treated in the Clinical Department of Infectious Diseases in the University Hospital Centre Split from 1979 to 2013. The main purpose of this research was to determine the epidemiological characteristics, clinical presentation, local and general complications, and received treatment. Most bites occurred during warm months, from early May to late August (80%), mostly in May and June. Upper limb bites were more frequent (59%) than lower limb bites (40%). Out of the total number of poisoned children, 24% developed local, and 25% general complications. The most common local complications were haemorrhagic blisters that occurred in 20% children, followed by compartment syndrome presented in 7.5% patients. The most dominated general complication was cranial nerve paresis or paralysis, which was identified in 11.2% patients, whereas shock symptoms were registrated in 7% children. According to severity of poisoning, 9.4% children had minor, 35% mild, 30.6% moderate, and 24.4% had severe clinical manifestation of envenomation. Only one (0.6%) child passed away because of snakebite directly on the neck. All patients received antivenom produced by the Institute of Immunology in Zagreb, tetanus prophylaxis as well, and almost all of them received antibiotics, and a great majority of them also received corticosteroids and antihistamines. Neighter anaphylactic reaction nor serum disease were noticed in our patients after administrating antivenom. A total of 26% children underwent surgical interventions, and incision of haemorrhagic blister was the most common applied surgical treatment, which was preformed in 15.6% patients, while fasciotomy was done in 7.5% subjects. All of our surgically treated patients recovered successfully.

Molecular systematics and undescribed diversity of Madagascan scolecophidian snakes (Squamata: Serpentes).

We provide an updated molecular phylogenetic analysis of global diversity of typhlopid and xenotyphlopid blindsnakes, adding a set of Madagascan samples and sequences of an additional mitochondrial gene to an existing supermatrix of nuclear and mitochondrial gene segments. Our data suggest monophyly of Madagascan typhlopids, exclusive of introduced Indotyphlops braminus. The Madagascar-endemic typhlopid clade includes two species previously assigned to the genus Lemuriatyphlops (in the subfamily Asiatyphlopinae), which were not each others closest relatives. This contradicts a previous study that described Lemuriatyphlops based on a sequence of the cytochrome oxidase subunit 1 gene from a single species and found this species not forming a clade with the other Malagasy species included. Based on our novel phylogenetic assessment we include all species in this endemic typhlopid clade in the genus Madatyphlops and in the subfamily Madatyphlopinae and consider Lemuriatyphlops as junior synonym. Within Madatyphlops, we identify several candidate species. For some of these (those in the M. arenarius complex), our preliminary data suggest sympatric occurrence and morphological differentiation, thus the existence of undescribed species. We also comment on the genus-level classification of several non-Madagascan typhlopids. We suggest that African species included in Madatyphlops (Afrotyphlops calabresii, A. cuneirostris, A. platyrhynchus, and Rhinotyphlops leucocephalus) should not be included in this genus. We furthermore argue that recent claims of Sundatyphlops, Antillotyphlops, and Cubatyphlops being "undiagnosable" or "not monophyletic" were based on errors in tree reconstruction and failure to notice diagnostic characters, and thus regard these three genera as valid.

Three new endemic species of Epictia Gray, 1845 (Serpentes: Leptotyphlopidae) from the dry forest of northwestern Peru.

Three new blind snake species of the genus Epictia are described based on material collected in the Peruvian Regions Amazonas, Cajamarca and La Libertad. All three species are well differentiated from all congeners based on characteristics of their morphology and coloration. They share 10 scale rows around the middle of the tail and possess two supralabials with the anterior one in broad contact with the supraocular. Epictia septemlineata sp. nov. has 16 subcaudal scales, 257 mid-dorsal scale rows, a yellowish-white rostral, and a black terminal spine. Epictia vanwallachi sp. nov. exhibits 16 subcaudals, 188 mid-dorsal scale rows, a grayish-brown rostral, and a yellow terminal spine. Epictia antoniogarciai sp. nov. features 14-18 subcaudals, 195-208 mid-dorsal scale rows, a bright yellow or yellowish-white rostral, and the terminal spine and terminal portion of the tail yellow. All three species were collected in the interandean dry forest valleys of the Marañón River and its tributaries. This region is an area of endemism and warrants further attention from systematic and conservation biologists.

A new blind snake (Serpentes: Typhlopidae) from an endangered habitat in south-eastern Queensland, Australia.

A new species of blind snake is described from south-eastern Queensland, eastern Australia. Anilios insperatus sp. nov. differs from all of its congeners in having:16 scales around the body; 442 paravertebral scales; snout slightly trilobed from above and bluntly angular in profile; small, inconspicuous eyes, located within the ocular scale at its junction with the preocular and the supraocular scales; and uniform light colouration. The unique specimen was collected from pasture that was formally Queensland regional ecosystem 12.8.24, a eucalypt dominated ecosystem currently listed as endangered. The site is less than 100 km from Queensland's capital, Brisbane. Given the locality, habitat and absence of additional specimens, the species is probably of conservation concern.

The Interplay between Environmental Filtering and Spatial Processes in Structuring Communities: The Case of Neotropical Snake Communities.

Both habitat filters and spatial processes can influence community structure. Space alone affects species immigration from the regional species pool, whereas habitat filters affect species distribution and inter-specific interactions. This study aimed to understand how the interplay between environmental and geographical processes influenced the structure of Neotropical snake communities in different habitat types. We selected six studies that sampled snakes in forests, four conducted in savannas and two in grasslands (the latter two are grouped in a non-forest category). We used the net relatedness and nearest taxon indices to assess phylogenetic structure within forest and non-forest areas. We also used the phylogenetic fuzzy-weighting algorithm to characterize phylogenetic structure across communities and the relation of phylogenetic composition patterns to habitat type, structure, and latitude. Finally, we tested for morphological trait convergence and phylogenetic niche conservatism using four forest and four non-forest areas for which morphological data were available. Community phylogenetic composition changed across forest and non-forest areas suggesting that environmental filtering influences community structure. Species traits were affected by habitat type, indicating convergence at the metacommunity level. Tail length, robustness, and number of ventral scales maximized community convergence among forest and non-forest areas. The observed patterns suggested environmental filtering, indicating that less vertically structured habitats represent a strong filter. Despite the fact that phylogenetic structure was not detected individually for each community, we observed a trend towards communities composed by more closely related species in higher latitudes and more overdispersed compositions in lower latitudes. Such pattern suggests that the limited distribution of major snake lineages constrained species distributions. Structure indices for each community were also related to habitat type, showing that communities from non-forest areas tend to be more clustered. Our study showed that both environmental filtering and spatial gradients play important roles in shaping the composition of Neotropical snake communities.

Optimal husbandry of hatchling Eastern Indigo Snakes (Drymarchon couperi) during a captive head-start program.

Optimal husbandry techniques are desirable for any headstart program, but frequently are unknown for rare species. Here we describe key reproductive variables and determine optimal incubation temperature and diet diversity for Eastern Indigo Snakes (Drymarchon couperi) grown in laboratory settings. Optimal incubation temperature was estimated from two variables dependent on temperature, shell dimpling, a surrogate for death from fungal infection, and deviation of an egg from an ovoid shape, a surrogate for death from developmental anomalies. Based on these relationships and size at hatching we determined optimal incubation temperature to be 26°C. Additionally, we used incubation data to assess the effect of temperature on duration of incubation and size of hatchlings. We also examined hatchling diets necessary to achieve optimal growth over a 21-month period. These snakes exhibited a positive linear relationship between total mass eaten and growth rate, when individuals were fed less than 1711 g of prey, and displayed constant growth for individuals exceeding 1711 g of prey. Similarly, growth rate increased linearly with increasing diet diversity up to a moderately diverse diet, followed by constant growth for higher levels of diet diversity. Of the two components of diet diversity, diet evenness played a stronger role than diet richness in explaining variance in hatchling growth. These patterns document that our goal of satiating snakes was achieved for some individuals but not others and that diets in which total grams consumed over the first 21 months of life is distributed equivalently among at least three prey genera yielded the fastest growth rates for hatchling snakes.