Dietary Correlates of the Origin and Radiation of Snakes

Stomach analyses of living families and of a fossil containingprey were used to address possible dietary correlates of thehistory of snakes. Aniliids, morphologically primitive amongliving snakes, feed on relatively heavy, elongate vertebrates.Large aniliids eat larger prey than do small individuals but,as in advanced snakes, they also take small items. Living boids,structurally intermediate between aniliids and advanced snakes,feed on relatively heavy prey of a much greater variety of shapesthan do aniliids. An Eocene fossil that might be a boid containsa relatively large crocodilian in its gut. These findings, previousstudies, and morphological considerations suggest that veryearly snakes used constriction and powerful jaws to feed onelongate, heavy prey. This would have permitted a shift fromfeeding often on small items to feeding rarely on heavy items,without initially requiring major changes in jaw structure relativeto a lizard-like ancestor. Subsequent morphological changescould then have allowed boids to utilize a broad range of preytypes, including many of those currently eaten by advanced snakes.More recent dietary themes include the consumption of even heavierprey by highly venomous elapids and viperids, and frequent feedingon relatively small items by some other advanced snakes.     

Feeding behavior and venom toxicity of coral snake Micrurus nigrocinctus (Serpentes: Elapidae) on its natural prey in captivity

The feeding behavior and venom toxicity of the coral snake Micrurus nigrocinctus (Serpentes: Elapidae) on its natural prey in captivity were investigated. Coral snakes searched for their prey (the colubrid snake Geophis godmani) in the cages. Once their preys were located, coral snakes stroke them with a rapid forward movement, biting predominantly in the anterior region of the body. In order to assess the role of venom in prey restraint and ingestion, a group of coral snakes was 'milked' in order to drastically reduce the venom content in their glands. Significant differences were observed between snakes with venom, i.e., 'nonmilked' snakes, and 'milked' snakes regarding their behavior after the bite. The former remained hold to the prey until paralysis was achieved, whereas the latter, in the absence of paralysis, moved their head towards the head of the prey and bit the skull to achieve prey immobilization by mechanical means. There were no significant differences in the time of ingestion between these two groups of coral snakes. Susceptibility to the lethal effect of coral snake venom greatly differed in four colubrid species; G. godmani showed the highest susceptibility, followed by Geophis brachycephalus, whereas Ninia psephota and Ninia maculata were highly resistant to this venom. In addition, the blood serum of N. maculata, but not that of G. brachycephalus, prolonged the time of death of mice injected with 2 LD(50)s of M. nigrocinctus venom, when venom and blood serum were incubated before testing. Subcutaneous injection of coral snake venom in G. godmani induced neurotoxicity and myotoxicity, without causing hemorrhage and without affecting heart and lungs. It is concluded that (a) M. nigrocinctus venom plays a role in prey immobilization, (b) venom induces neurotoxic and myotoxic effects in colubrid snakes which comprise part of their natural prey, and (c) some colubrid snakes of the genus Ninia present a conspicuous resistance to the toxic action of M. nigrocinctus venom.     

DID EGG‐LAYING BOAS BREAK DOLLO'S LAW? PHYLOGENETIC EVIDENCE FOR REVERSAL TO OVIPARITY IN SAND BOAS (ERYX: BOIDAE)

Re-evolution of lost complex morphological characters has been proposed for several characters, including insect wings, limbs, eyes in snakes, and digits in lizards, among others. There has also been much interest in whether the transition from oviparity to viviparity is reversible, particularly in squamate reptiles where the transition to viviparity has occurred more times than in any other lineage. Here, we present a phylogenetic analysis of boid snakes based on a concatenated multigene study of all genera of erycines, New and Old World boines, plus other groups thought to be closely related with boines such as monotypic species Calabaria and Casarea . We reconstruct ancestral parity mode on this phylogeny and present statistical evidence that oviparity reevolved in a species of Old World sand boa in the genus Eryx nearly 60 million years after the initial boid transition to viviparity. Remarkably, like other viviparous boas hatchlings of oviparous Eryx lack an egg-tooth providing independent evidence that oviparity is a derived state in these species.     

Snake phylogeny based on osteology,soft anatomy and ecology

Relationships between the major lineages of snakes are assessed based on a phylogenetic analysis of the most extensive phenotypic data set to date (212 osteological, 48 soft anatomical, and three ecological characters). The marine, limbed Cretaceous snakes Pachyrhachis and Haasiophis emerge as the most primitive snakes: characters proposed to unite them with advanced snakes (macrostomatans) are based on unlikely interpretations of contentious elements or are highly variable within snakes. Other basal snakes include madtsoiids and Dinilysia--both large, presumably non-burrowing forms. The inferred relationships within extant snakes are broadly similar to currently accepted views, with scolecophidians (blindsnakes) being the most basal living forms, followed by anilioids (pipesnakes), booids and booid-like groups, acrochordids (filesnakes), and finally colubroids. Important new conclusions include strong support for the monophyly of large constricting snakes (erycines, boines. pythonines), and moderate support for the non-monophyly of the trophidophiids' (dwarf boas). These phylogenetic results are obtained whether varanoid lizards, or amphisbaenians and dibamids, are assumed to be the nearest relatives (outgroups) of snakes, and whether multistate characters are treated as ordered or unordered. Identification of large marine forms, and large surface-active terrestrial forms, as the most primitive snakes contradicts with the widespread view that snakes arose via minute, burrowing ancestors. Furthermore, these basal fossil snakes all have long flexible jaw elements adapted for ingesting large prey ('macrostomy'), suggesting that large gape was primitive for snakes and secondarily reduced in the most basal living foms (scolecophidians and anilioids) in connection with burrowing. This challenges the widespread view that snake evolution has involved progressive, directional elaboration of the jaw apparatus to feed on larger prey.     

Eye size variation reflects habitat and daily activity patterns in colubrid snakes

The functioning of the vertebrate eye depends on its absolute size, which is presumably adapted to specific needs. Eye size variation in lidless and spectacled colubrid snakes was investigated, including 839 specimens belonging to 49 genera, 66 species and subspecies. Variations of adult eye diameters (EDs) in both absolute and relative terms between species were correlated with parameters reflecting behavioral ecology. In absolute terms, eye of arboreal species was larger than in terrestrial and semiaquatic species. For diurnal species, EDs of terrestrial species do not differ from semiaquatic species; for nocturnal species the ED of terrestrial species is larger than fossorial species but not different from semiaquatic species. In relative terms, ED did not differ significantly by habitat for diurnal species. Although the ED of terrestrial species is larger than fossorial species there were no differences for nocturnal species between semiaquatic and fossorial snakes. In contrast to other vertebrates studied to date, colubrid EDs in absolute and relative terms are larger in diurnal than in nocturnal species. These observations suggest that among colubrid snakes, eye size variation reflects adaptation to specific habitats, foraging strategies and daily activities, independently of phylogeny. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

Gripping during climbing of arboreal snakes may be safe but not economical

On the steep surfaces that are common in arboreal environments, many types of animals without claws or adhesive structures must use muscular force to generate sufficient normal force to prevent slipping and climb successfully. Unlike many limbed arboreal animals that have discrete gripping regions on the feet, the elongate bodies of snakes allow for considerable modulation of both the size and orientation of the gripping region. We quantified the gripping forces of snakes climbing a vertical cylinder to determine the extent to which their force production favoured economy or safety. Our sample included four boid species and one colubrid. Nearly all of the gripping forces that we observed for each snake exceeded our estimate of the minimum required, and snakes commonly produced more than three times the normal force required to support their body weight. This suggests that a large safety factor to avoid slipping and falling is more important than locomotor economy.     

An immunocytochemical study of endocrine pancreas of snakes

Summary The pancreas from eleven species of snakes representing both advanced and primitive families has been investigated for the presence of eleven regulatory peptides reported to occur in the mammalian endocrine pancreas. Of the eleven peptides studied, insulin, pancreatic glucagon and somatostatin were present in endocrine cells within the islets of all the species investigated. The neuropeptide, vasoactive intestinal polypeptide, was located within nerve terminals innervating the islets in the Boidinae, Colubrinae, Elaphidae and Crotalidae but absent from the Natricinae investigated.No immunoreactivity was demonstrable with the antisera to substance P, met-enkephalin, C-terminal gastrin, bombesin, glicentin and gastric inhibitory polypeptide. Pancreatic polypeptide-like immunoreactivity was demonstrable only in the boid snakes and exclusively stained by a C-terminal specific antiserum.     

Chromosomal evolution in serpentes; a comparison of G and C chromosome banding patterns of some colubrid and boid genera

G and C-chromosome banding techniques have been used to compare the structure of the karyotype in a variety of colubrid and boid snakes. The comparison of G-band patterns indicates that while some band sequences have been conserved, either as whole chromosomes or entire arms, there is also evidence of considerable rearrangement especially in the smaller chromosomes. In the colubrid Elaphe subocularis there is also evidence that there has been a relocation of the centromere on chromosome 2 without any accompanying inversion in the sequence of G-bands. Finally, G-banding has facilitated the demonstration of a simple pericentric inversion distinguishing the Z and W chromosomes in Acrantophis dumereli. This represents the first report of differentiated sex chromosomes in a boid snake. The combined banding data thus indicates that snake chromosomes are certainly not lacking in variability. The use of C-banding to detect constitutive heterochromatin has confirmed that in some boids and colubrids macrochromosomes have been derived from microchromosomes by the additions of heterochromatin.     

Molecular systematics of New World lampropeltinine snakes (Colubridae): implications for biogeography and evolution of food habits

We used mitochondrial gene sequences to infer phylogenetic relationships among North American snakes of the colubrid tribe Lampropeltini (Arizona, Bogertophis, Cemophora , New World Elaphe, Lampropellis, Pituophis, Rhinocheilus, Senticolis, Stilosoma) , and assessed the implications of our findings for the biogeography and evolution of food habits among these serpents. The maximum likelihood phylogeny identified Rhinocheilus as the sister taxon to all other lampropeltinines, and supported the monophyly of Lampropeltis (including Stilosoma) , New World Elaphe , and Pituophis , but not that of Bogertophis. This phylogeny also suggested a sister group relationship between Cemophora and Lampropeltis , and between New World Elaphe and Pituophis , and strongly supported that Sentkolis belongs within Lampropeltini, thus contradicting previous suggestions that Senticolis is not a lampropeltinine. Using a method for approximating ancestral areas of clades, we determined that western North America was most likely the ancestral area of lampropeltinines. Our survey of published studies, combined with unpublished data, indicated that lampropeltinines as a group feed mainly on mammals, less frequently on lizards, birds, and bird eggs, and only rarely on squamate eggs, snakes, anurans, and insects. Some individual species indeed emphasize mammals in their diets, but others most frequently eat lizards, squamate eggs, bird eggs, or snakes, whereas others take two prey types with similar frequency. Our reconstruction of the evolution of food habits among lampropeltinines suggests that a diet emphasizing lizards is ancestral, and therefore diets that mosdy consist of mammals, squamate and bird eggs, and snakes are derived within the clade. In at least some species, smaller individuals prey mostly on lizards and larger ones add mammals to their diets.     

Helminth infracommunity structure of the sympatric garter snakes Thamnophis eques and Thamnophis melanogaster from the Mesa Central of Mexico

Seventy-two Mexican garter snakes (Thamnophis eques) and 126 black-bellied garter snakes (T. melanogaster) were collected from 4 localities of the Mesa Central of Mexico between July 1996 and February 1998 and examined for helminths. Both species of garter snakes occurred sympatrically in every locality except in Lake Cuitzeo. Both species of snakes shared 9 helminth species, and in general, T. melanogaster hosted a larger number of species than T. eques. In each locality, a different helminth species showed the highest levels of prevalence and abundance (Spiroxys susanae in Ciénaga de Lerma, Telorchis corti in Lago de Pátzcuaro, Proteocephalus variabilis in Lago de Cuitzeo, and Contracaecum sp. in Lago de Chapala). Helminth communities in garter snakes of the Mesa Central are depauperate and dominated by a single parasite species. In those localities where the snakes occurred in sympatry, helminth communities were, in general, more diverse and species-rich in T. melanogaster. Differences in the ecology and physiology of these species of garter snakes may explain this pattern because black-bellied garter snakes (T. melanogaster) are more aquatic than Mexican garter snakes (T. eques) and primarily eat aquatic prey, potentially exposing themselves to a larger number of helminths transmitted by predator-prey infection. The helminth infracommunities of garter snakes in the Mesa Central of Mexico show a strong Nearctic influence because most of the species infecting these hosts have been recorded in other Nearctic colubrid snakes. However, the helminth infracommunities of these garter snakes are less species-rich and less diverse than those in colubrid snakes in more temperate latitudes. The widespread ecological perturbation of sampling sites in the Mesa Central because of human activity, and geographic differences in foraging ecology of the hosts and, thus, exposure to parasites transmitted by intermediate hosts may help to explain these patterns.     

The Cochlear Duct of Lizards and Snakes

The gross morphology of the cochlear ducts of approximatelyhalf (150) of the living genera of lizards and a third (130)of the living genera of snakes have been studied. The differencesin the structure of the cochlear duct are related to both theacoustical capacities and the taxonomic relationships of certainlizards and snakes. The cochlear duct of lizards consists offairly well joined lagenar and limbic portions. By contrast,the cochlear duct of snakes consists of a lagenar sac somewhatconstricted from the limbus. Each family of lizards has a morphologicallycharacteristic cochlear duct, but taxonomic relationships areindicated by certain anatomical similarities. The cochlear ductof snakes is more primitive than that of lizards, and, unlikelizards, does not exhibit marked specializations of its variousparts. Differences in morphology of the cochlear duct in snakesare much more related to habitat than family. The limbus andpapilla basilaris of snakes regardless of family, are most elongatedin bin rowing species, are only moderately elongated or ovoidin terrestrial species, and are small or reduced in certainarboreal and aquatic species.     

The phylogeny and classification of caenophidian snakes inferred from seven nuclear protein-coding genes

More than 80% of the approximately 3000 living species of snakes are placed in the taxon Caenophidia (advanced snakes), a group that includes the families Acrochordidae, Viperidae, Elapidae, Atractaspididae, and the paraphyletic 'Colubridae'. Previous studies using DNA sequences have involved few nuclear genes (one or two). Several nodes have therefore proven difficult to resolve with statistical significance. Here, we investigated the higher-level relationships of caenophidian snakes with seven nuclear protein-coding genes and obtained a well-supported topology. Accordingly, some adjustments to the current classification of Caenophidia are made to better reflect the relationships of the groups. The phylogeny also indicates that, ancestrally, caenophidian snakes are Asian and nocturnal in origin, although living species occur on nearly all continents and are ecologically diverse.     

蜡嘴,锡嘴雀和法国鹌鹑耳蜗—中脑听觉中枢的比较观察

用辣根过氧化物酶HRP顺行标记方法表明蜡嘴(Eophona migratoria)、锡嘴(Coccothra-ustes coccothraustes)和鹌鹑(France Coturnix coturnix)脑干内听觉中枢的初级神经元位于耳蜗核(nCO,Cochlear unclei)内。较高级神经元位于中脑背外侧核(MLD,Nucleus mesen-cephalicus lateralis,pars dorsalis)。脑干内听觉传入通路始于nCO,经外侧丘系(LL,Lemni-scus lateralis)可直接投射于MLD。鸣禽鸟蜡嘴、锡嘴是对侧投射,同侧仅有个别纤维被标记,非鸣禽鹌鹑仅是对侧性投射。     

Influence of the venom delivery system on intraoral prey transport in snakes

We compared intraoral prey transport in venomous snake species from four families (two atractaspidids, nine elapids, three colubrids, 44 viperids) with that in eight non-venomous colubrid species, most feeding on similar mammalian prey. The morphology of the venom delivery system suggests that intraoral prey transport performance should be slightly decreased in atractaspidids, unmodified in most elapids and venomous colubrids, and increased or unmodified in vipers, as compared to that in non-venomous colubrid snakes. Our measurements of relative intraoral prey transport performance show that differences among families do not match expectations based on morphology or past studies. Decreased performance in Atractaspis results from reduction and loss of teeth on the medial palatal elements and dentaries, but affects only early phases of ingestion. Although joint and bone features of elapids and colubrids are similar, intraoral prey transport performance is significantly lower in elapids than in colubrids. Predicted enhancement of intraoral prey transport performance in vipers as compared to colubrids was not borne out by measurements, presumably because palatopterygoid movement during intraoral prey transport is reduced in many viper species to limit fang erection. Absence of significant performance differences between colubrids and viperids might suggest that evolution of the viperid venom delivery system was subject to little selection pressure from intraoral prey transport. Another possibility is that there are trade-offs between intraoral prey transport and strike performance in vipers related to relative skull mass and jaw fragility. Immobilizing prey prior to intraoral transport places less demand on transport performance in vipers. In this model, the conservative kinesis and greater robustness of the colubrid palate has greater potential for transporting live prey with less risk of injury.     

Testing the 'free radical theory of aging' hypothesis: physiological differences in long-lived and short-lived colubrid snakes

We test the 'free radical theory of aging' using six species of colubrid snakes (numerous, widely distributed, non-venomous snakes of the family Colubridae) that exhibit long (> 15 years) or short (< 10 years) lifespans. Because the 'rate of living theory' predicts metabolic rates to be correlated with rates of aging and oxidative damage results from normal metabolic processes we sought to answer whether physiological parameters and locomotor performance (which is a good predictor of survival in juvenile snakes) mirrored the evolution of lifespans in these colubrid snakes. We measured whole animal metabolic rate (oxygen consumption Vo2), locomotor performance, cellular metabolic rate (mitochondrial oxygen consumption), and oxidative stress potential (hydrogen peroxide production by mitochondria). Longer-lived colubrid snakes have greater locomotor performance and reduced hydrogen peroxide production than short-lived species, while whole animal metabolic rates and mitochondrial efficiency did not differ with lifespan. We present the first measures testing the 'free radical theory of aging' using reptilian species as model organisms. Using reptiles with different lifespans as model organisms should provide greater insight into mechanisms of aging.     

The diets of Hispaniolan colubrid snakes

Summary Approximately 1590 Hispaniolan colubrid snakes representing six genera and eight species were examined for prey remains (Alsophis cantherigerus, Antillophis parvifrons, Darlingtonia haetiana, Hypsirhynchus ferox, Ialtris dorsalis, Uromacer catesbyi, U. frenatus, and U. oxyrhynchus). The snakes were collected at many localities over a span of 80 years.Of 426 prey items, 77.9% were lizards (of which 69.6% were anoles), 19% frogs, 2.6% birds and mammals, and 0.5% other snakes. Darlingtonia was the only snake that did not exploit lizards; it fed exclusively on Eleutherodactylus frogs, including egg clutches. Disregarding Darlingtonia, there is no size class of Hispaniolan colubrids between 20–90 cm SVL that does not prey primarily on Anolis. Certain prey genera are added to, or deleted from, diets depending on snake size, but the data suggest that snake SVL alone does little to dictate what prey genera (or groups) are eaten. Shannon-Wiener values (H') indicate that Darlingtonia has the narrowest trophic niche, while Alsophis and Ialtris have the widest. Values of H' are not correlated with snake SVL, but highly significant (P<0.001) correlations exist between H' and mid-body circumference, head width, and snout width, and these characters may be indicators of trophic generalists and specialists. Anolis lizards are the most ubiquitous and conspicuous vertebrates on Hispaniola, and it is not surprising that they are widely exploited as a food source. Although as some snake species grow larger, anoles play a decreasingly important role in their diets, there is no evidence to suggest that they are ever abandoned as a food source by any Hispaniolan colubrid of any size.Secretive lizards of low vagility are eaten almost exclusively by wide ranging foragers (Alsophis, Antillophis); very active prey (Ameiva) is taken by sit-and-wait strategists (Hysirhynchus, U. frenatus). Those snakes which exploit the most prey groups are active foragers. Uromacer catesbyi exhibits both foraging modes, and predictably, eats diurnally active (anoles) and diurnally quiescent (hylid frogs) prey with almost equal frequency.Within Maglio's cantherigerus species assemblage, in which an Alsophis cantherigerus-like snake was ancestral to the other species, and in which longsnouted Uromacer are the most morphologically derived, there is an obvious trend toward trophic specialization on Hispaniola. The West Indies have provided an ideal natural laboratory for the investigation of many aspects of vertebrate ecology, and an arena in which to test theories of island biogeography. The most extensively studied West Indian vertebrates have been the lizards of the iguanid genus Anolis. Conversely, the ecology of West Indian snakes has been largely ignored. This is surprising in light of the fact that much has been written about Anolis predation, but little has been written about predators of Anolis; snakes may be important, frequent consumers of anoles.Hispaniola is physiographically and ecologically the most diverse of the Greater Antilles and, concomitantly, it has the most diverse snake fauna, including six colubrid genera containing 11 described species. It has rich frog and lizard faunas, but only two endemic mammals. Study of the diets of Hispaniola's colubrid snakes was undertaken to gain initial insights into the ecology of the snakes and to determine 1) what the snakes eat; 2) what relationships exist between snake diet and snake size as well as head and body proportions; 3) what relationships exist between snake foraging mode and prey type and size; 4) if anoles, as the most ubiquitous and conspicuous vertebrates on Hispaniola, comprise an important source of food; 5) if significant geographical differences in diet exist, expecially on satellite islands; 6) if north island and south island (sensu Williams 1961) Anolis ecomorphs are preyed upon by the same snake species in similar proportions; 7) if snakes are selective or opportunistic predators.This paper, the first in a series that will address all of the above topics, will briefly describe methods, snake species and prey genera. Prey genera are analyzed in terms of what snake taxa prey upon them, what size classes of snakes prey upon them, and prey genera diversity versus snake size and proportions.     

Specializations of the Body Form and Food Habits of Snakes

Viperid snakes have stouter bodies, larger heads, and longerjaws than snakes in other families; there are no major differencesbetween the two subfamilies of vipers in these features. A suiteof morphological characters that facilitates swallowing largeprey finds its greatest expression among vipers, but certainelapid and colubrid snakes have converged upon the same bodyform. The number of jaw movements required to swallow prey islinearly related to the size of a prey item when shape is heldconstant. Very small and very large prey are not disproportionatelydifficult for a snake to ingest. Vipers swallow their prey withfewer jaw movements than do colubrids or boids and can swallowprey that is nearly three times larger in relation to theirown size. Proteolytic venom assists in digestion of prey, andmelanin deposits shield the venom glands from light that woulddegrade the venom stores. Ancillary effects of the morphologicalfeatures of vipers, plus the ability to ingest a very largequantity of food in one meal, should produce quantitative andqualitative differences in the ecology and behavior of vipersand other snakes.     

ZW,XY, and yet ZW: Sex chromosome evolution in snakes even more complicated

Snakes are historically important in the formulation of several central concepts on the evolution of sex chromosomes. For over 50 years, it was believed that all snakes shared the same ZZ/ZW sex chromosomes, which are homomorphic and poorly differentiated in “basal” snakes such as pythons and boas, while heteromorphic and well differentiated in “advanced” (caenophidian) snakes. Recent molecular studies revealed that differentiated sex chromosomes are indeed shared among all families of caenophidian snakes, but that boas and pythons evolved likely independently male heterogamety (XX/XY sex chromosomes). The historical report of heteromorphic ZZ/ZW sex chromosomes in a boid snake was previously regarded as ambiguous. In the current study, we document heteromorphic ZZ/ZW sex chromosomes in a boid snake. A comparative approach suggests that these heteromorphic sex chromosomes evolved very recently and that they are poorly differentiated at the sequence level. Interestingly, two snake lineages with confirmed male heterogamety possess homomorphic sex chromosomes, but heteromorphic sex chromosomes are present in both snake lineages with female heterogamety. We point out that this phenomenon is more common across squamates. The presence of female heterogamety in non‐caenophidian snakes indicates that the evolution of sex chromosomes in this lineage is much more complex than previously thought, making snakes an even better model system for the evolution of sex chromosomes.     

Evolution of sex-chromosomes and formation of W-chromatin in snakes

The analysis of sex-chromosome complexes and formation of W-chromatin in 16 species of snakes of the families Boidae, Colubridae, Elapidae, and Hydrophiidae, reveal three very pertinent facts. First, the snakes exhibit various states of the differentiation of the Z and W chromosomes, apparently according to the evolutionary status of the families, being homomorphic in primitive families and well differentiated in highly evolved ones. Second, the demonstration of a heteropycnotic body in the interphase nuclei of the families of a large number of species of snakes has definitely shown that the nuclear sexing is possible not only in those species of snakes where the W chromosome is morphologically distinguishable from the Z, but also in those species where it is not so, but shows an asynchrony in the replicating pattern of W. It is suggested that development of allocycly rather than establishment of structural changes is the first step in the differentiation of the W from the Z in snakes. Third, the absence of coexistence of nucleolus and W-chromatin in a condensed state in the interphase nuclei of different tissues in a few species of snakes reported in this paper suggests that the W-chromatin is responsible for the synthesis of the nucleolus in these snakes.Paper presented at the Third Oxford Chromosome Conference, September, 1970.     

Are Diet Preferences Associated to Skulls Shape Diversification in Xenodontine Snakes?

Snakes are a highly successful group of vertebrates, within great diversity in habitat, diet, and morphology. The unique adaptations for the snake skull for ingesting large prey in more primitive macrostomatan snakes have been well documented. However, subsequent diversification in snake cranial shape in relation to dietary specializations has rarely been studied (e.g. piscivory in natricine snakes). Here we examine a large clade of snakes with a broad spectrum of diet preferences to test if diet preferences are correlated to shape variation in snake skulls. Specifically, we studied the Xenodontinae snakes, a speciose clade of South American snakes, which show a broad range of diets including invertebrates, amphibians, snakes, lizards, and small mammals. We characterized the skull morphology of 19 species of xenodontine snakes using geometric morphometric techniques, and used phylogenetic comparative methods to test the association between diet and skull morphology. Using phylogenetic partial least squares analysis (PPLS) we show that skull morphology is highly associated with diet preferences in xenodontine snakes.