The colouration of the venomous coral snakes (family Elapidae) and their mimics (families Aniliidae and Golubridae)

The bright coloured, highly venomous coral snakes, Leptomicrurus, Micrurus and Micruroides (family Elapidae) and a series of harmless or mildly toxic mimics form an important component of the snake fauna of the Americas. Coral snake patterns are defined as any dorsal pattern found in any species of venomous coral snake and/or any dorsal pattern containing a substantial amount of red, pink or orange distributed so as to resemble that of some species of venomous coral snake. The components of coral snake colouration are described and four principal dorsal patterns are recognized: unicolour, bicolour, tricolour and quadricolour. The tricolour patterns may be further clustered based on the number of black bands or rings separating the red ones as: monads, dyads, triads, tetrads or pentads. A detailed classification of all coral snake colour patterns is presented and each pattern is illustrated. The taxonomic distribution of these patterns is surveyed for mimics and the 56 species of highly venomous coral snakes. Among the latter, the most frequent encountered patterns are tricolour monads, tricolour triads and bicolour rings, in that order. No venomous coral snakes have a tricolour dyad, tricolour tetrad or quadricolour pattern. As many as 115 species of harmless or mildly toxic species, c. 18% of all American snakes, are regarded as coral snake mimics. The colouration and behavioural traits of venomous coral snakes combine to form a significant antipredator defence of an aposematic type. The mimics in turn receive protection from predators that innately or through learning avoid coral snake colour patterns. The precise resemblances in colouration between sympatric non-coral snakes and venomous coral snakes and the concordant geographic variation between the two strongly support this view. Batesian mimicry with the highly venomous coral snakes as the models and the other forms as the mimics is the favoured explanation for this situation. It is further concluded that a number of species in the genera Elaphe, Farancia, Nerodia and Thamnophis, although having red in their colouration, should not be included in the coral snake mimic guild.     

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.     

Phylogenetic relationships of North American garter snakes (Thamnophis) based on four mitochondrial genes: how much DNA sequence is enough?

The clade of garter snakes (Thamnophis) includes some of the most abundant and well-studied snakes in North America. However, phylogenetic relationships within this group have been little studied. We used DNA sequences of four mitochondrial genes (cytochrome b and NADH dehydrogenase subunits 1, 2, and 4) to estimate relationships among 29 of the 31 recognized species of Thamnophis plus the related species Adelophis foxi. Both maximum parsimony (MP) and maximum-likelihood (ML) analyses of all these genes combined produced well-resolved trees with moderate (70-89%) to strong (90-100%) bootstrap support for most clades. MP and ML trees were very similar, with no strongly supported conflict between the two analyses. These analyses identify a clade of 12 species largely restricted to México (the "Mexican clade"), and a clade containing 15 species that collectively range from Central America to southern Canada (the "widespread clade"). These two groups are identified as sister taxa in both MP and ML analyses. A clade consisting of the ribbon snakes (T. sauritus and T. proximus) and the common garter snake (T. sirtalis) is placed as the sister group to all other Thamnophis (i.e., the Mexican + widespread clades) in our analyses. High bootstrap proportions at several levels in the tree support the inclusion of both Thamnophis validus, which has traditionally been placed in the genus Nerodia, and the poorly known species Adelophis foxi within Thamnophis. We used randomly sampled characters (i.e., standard bootstrapping) and randomly sampled contiguous blocks of characters to examine the effect of number of characters on resolution of and support for relationships within Thamnophis using MP. In general, these analyses indicate that we have reached a point of strongly diminishing returns with respect to the effect of adding mtDNA sequence characters for the current set of taxa; our sample of 3809 mtDNA characters is apparently "enough." The next steps to improve the phylogenetic estimate may be to add nuclear DNA sequences, morphology, or behavior, or to sequence additional mtDNA lineages within species.     

Phylogenetic relationships of the dwarf boas and a comparison of Bayesian and bootstrap measures of phylogenetic support

Four New World genera of dwarf boas (Exiliboa, Trachyboa, Tropidophis, and Ungaliophis) have been placed by many systematists in a single group (traditionally called Tropidophiidae). However, the monophyly of this group has been questioned in several studies. Moreover, the overall relationships among basal snake lineages, including the placement of the dwarf boas, are poorly understood. We obtained mtDNA sequence data for 12S, 16S, and intervening tRNA-val genes from 23 species of snakes representing most major snake lineages, including all four genera of New World dwarf boas. We then examined the phylogenetic position of these species by estimating the phylogeny of the basal snakes. Our phylogenetic analysis suggests that New World dwarf boas are not monophyletic. Instead, we find Exiliboa and Ungaliophis to be most closely related to sand boas (Erycinae), boas (Boinae), and advanced snakes (Caenophidea), whereas Tropidophis and Trachyboa form an independent clade that separated relatively early in snake radiation. Our estimate of snake phylogeny differs significantly in other ways from some previous estimates of snake phylogeny. For instance, pythons do not cluster with boas and sand boas, but instead show a strong relationship with Loxocemus and Xenopeltis. Additionally, uropeltids cluster strongly with Cylindrophis, and together are embedded in what has previously been considered the macrostomatan radiation. These relationships are supported by both bootstrapping (parametric and nonparametric approaches) and Bayesian analysis, although Bayesian support values are consistently higher than those obtained from nonparametric bootstrapping. Simulations show that Bayesian support values represent much better estimates of phylogenetic accuracy than do nonparametric bootstrap support values, at least under the conditions of our study.     

Soft anatomy, diffuse homoplasy, and the relationships of lizards and snakes

Most previous phylogenetic analyses of squamates (‘lizards’ and snakes) employing large character sets have focused on osteology. Soft anatomical traits bearing on this problem have usually been considered in small subsets. Here, a comprehensive phylogenetic analysis of squamate soft anatomy is attempted. 126 informative characters are assessed for 23 squamate lineages, representing snakes, amphisbaenians, dibamids, and all the traditionally recognized ‘families’ of lizards. The traditionally recognized groupings Iguania, Scleroglossa, Gekkota, Scincomorpha, Anguimorpha and Varanoidea are corroborated in this analysis. More controversial taxa are resolved as follows. Xantusiids, amphisbaenians and dibamids cluster with gekkotans, and snakes are strongly allied with anguimorphs in general, and varanids in particular. Nearly all these clades are congruent with those found in a recent comprehensive osteological analysis; the strong support for snake‐varanid relationships found in both studies is particularly notable. This congruence is surprising given that previous studies of soft anatomy tended to give differing and often heterodox results. These previous results can be attributed to overrepresentation of misleading characters in small isolated data sets. Such misleading signals are minimized when data sets are combined. For instance, the snake‐varanid clade is contradicted by many characters, and analyses of particular organ systems therefore give differing results. However, characters that are incongruent with the snake‐varanid clade also disagree with each other (diffuse homoplasy), rather than forming coherent support for some particular alternative clade (concerted homoplasy). In a combined analysis these incongruent but diffuse characters cancel each other out to leave a very strong (and orthodox) phylogenetic signal. These results underscore the view that the raw amount of homoplasy — as revealed by consistency and retention indices — is not the only determinant of phylogenetic signal; the distribution of that homoplasy is also important. Thus, questioning a phylogenetic hypothesis (e.g. the snake‐varanid clade) by identifying numerous conflicting characters is insufficient — the structure of the conflicting characters should be assessed in a rigorous phylogenetic analysis.     

Trophic divergence despite morphological convergence in a continental radiation of snakes

Ecological and phenotypic convergence is a potential outcome of adaptive radiation in response to ecological opportunity. However, a number of factors may limit convergence during evolutionary radiations, including interregional differences in biogeographic history and clade-specific constraints on form and function. Here, we demonstrate that a single clade of terrestrial snakes from Australia—the oxyuranine elapids—exhibits widespread morphological convergence with a phylogenetically diverse and distantly related assemblage of snakes from North America. Australian elapids have evolved nearly the full spectrum of phenotypic modalities that occurs among North American snakes. Much of the convergence appears to involve the recurrent evolution of stereotyped morphologies associated with foraging mode, locomotion and habitat use. By contrast, analysis of snake diets indicates striking divergence in feeding ecology between these faunas, partially reflecting regional differences in ecological allometry between Australia and North America. Widespread phenotypic convergence with the North American snake fauna coupled with divergence in feeding ecology are clear examples of how independent continental radiations may converge along some ecological axes yet differ profoundly along others.     

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.     

Molecular systematics and evolution of Regina and the thamnophiine snakes.

Snakes of the tribe Thamnophiini represent an ecologically important component of the herpetofauna in a range of habitats across North America. Thamnophiines are the best-studied colubrids, yet little is known of their systematic relationships. A molecular phylogenetic study of 32 thamnophiine species using three complete mitochondrial genes (cytochrome b, NADH dehydrogenase subunit 2, and 12S ribosomal DNA) recovered a well-supported phylogeny with three major clades: a garter snake group, a water snake group, and a novel semifossorial group. The historically contentious genus Regina, which contains the crayfish-eating snakes, is polyphyletic. The phylogeographic pattern of Thamnophis is consistent with an hypothesis of at least one invasion of northern North America from Mexico.     

Phylogenetic relationships of elapid snakes based on cytochrome b mtDNA sequences

Published molecular phylogenetic studies of elapid snakes agree that the marine and Australo-Melanesian forms are collectively monophyletic. Recent studies, however, disagree on the relationships of the African, American, and Asian forms. To resolve the relationships of the African, American, and Asian species to each other and to the marine/Australo-Melanesian clade, we sequenced the entire cytochrome b gene for 28 elapids; 2 additional elapid sequences from GenBank were also included. This sample includes all African, American, and Asian genera (except for the rare African Pseudohaje), as well as a representative sample of marine/Australo-Melanesian genera. The data were analyzed by the methods of maximum-parsimony and maximum-likelihood. Both types of analyses yielded similar trees, from which the following conclusions can be drawn: (1) Homoroselaps falls outside a clade formed by the remaining elapids; (2) the remaining elapids are divisible into two broad sister clades, the marine/Australo-Melanesian species vs the African, American, and Asian species; (3) American coral snakes cluster with Asian coral snakes; and (4) the "true" cobra genus Naja is probably not monophyletic as the result of excluding such genera as Boulengerina and Paranaja.     

Molecular Systematics and Evolution of Regina and the Thamnophiine Snakes

Snakes of the tribe Thamnophiini represent an ecologically important component of the herpetofauna in a range of habitats across North America. Thamnophiines are the best-studied colubrids, yet little is known of their systematic relationships. A molecular phylogenetic study of 32 thamnophiine species using three complete mitochondrial genes (cytochrome b, NADH dehydrogenase subunit 2, and 12S ribosomal DNA) recovered a well-supported phylogeny with three major clades: a garter snake group, a water snake group, and a novel semifossorial group. The historically contentious genus Regina, which contains the crayfish-eating snakes, is polyphyletic. The phylogeographic pattern of Thamnophis is consistent with an hypothesis of at least one invasion of northern North America from Mexico.     

Phylogeny of snake trypanosomes inferred by SSU rDNA sequences, their possible transmission by phlebotomines, and taxonomic appraisal by molecular, cross-infection and morphological analysis

Blood examination by microhaematocrit and haemoculture of 459 snakes belonging to 37 species revealed 2.4% trypanosome prevalence in species of Viperidae (Crotalus durissus and Bothrops jararaca) and Colubridae (Pseudoboa nigra). Trypanosome cultures from C. durissus and P. nigra were behaviourally and morphologically indistinguishable. In addition, the growth and morphological features of a trypanosome from the sand fly Viannamyia tuberculata were similar to those of snake isolates. Cross-infection experiments revealed a lack of host restriction, as snakes of 3 species were infected with the trypanosome from C. durissus. Phylogeny based on ribosomal sequences revealed that snake trypanosomes clustered together with the sand fly trypanosome, forming a new phylogenetic lineage within Trypanosoma closest to a clade of lizard trypanosomes transmitted by sand flies. The clade of trypanosomes from snakes and lizards suggests an association between the evolutionary histories of these trypanosomes and their squamate hosts. Moreover, data strongly indicated that these trypanosomes are transmitted by sand flies. The flaws of the current taxonomy of snake trypanosomes are discussed, and the need for molecular parameters to be adopted is emphasized. To our knowledge, this is the first molecular phylogenetic study of snake trypanosomes.     

A new Late Cretaceous snake from Patagonia: Phylogeny and trends in body size evolution of madtsoiid snakes

Madtsoiids constitute a successful group of extinct snakes widely distributed across Gondwana and the European archipelago during Late Cretaceous times, surviving in reduced numbers to the Pleistocene. They are renowned for including some of the largest snakes that have ever crawled on earth, yet diverse small madtsoiids are also known. Uncovering the evolutionary trends that led these snakes into disparate body sizes has been hampered mainly by the lack of phylogenetic consensus and the paucity of taxa with novel combinations of features. Here we describe a new large madtsoiid snake based on isolated vertebrae from the La Colonia Formation (Maastrichtian–Danian) of Patagonia, Argentina. A comprehensive phylogenetic analysis recovers Madtsoiidae as a basal ophidian lineage and the new snake as sister to a clade of mostly big-to-gigantic taxa, providing insights into early stages and evolutionary trends towards madtsoiid gigantism.     

An Examination of Scale-Dependent Resource Use by Eastern Hognose Snakes in Southcentral New Hampshire

ABSTRACT The decline of many snake populations is attributable to habitat loss, and knowledge of habitat use is critical to their conservation. Resource characteristics (e.g., relative availability of different habitat types, soils, and slopes) within a landscape are scale-dependent and may not be equal across multiple spatial scales. Thus, it is important to identify the relevant spatial scales at which resource selection occurs. We conducted a radiotelemetry study of eastern hognose snake (Heterodon platirhinos) home range size and resource use at different hierarchical spatial scales. We present the results for 8 snakes radiotracked during a 2-year study at New Boston Air Force Station (NBAFS) in southern New Hampshire, USA, where the species is listed by the state as endangered. Mean home range size (minimum convex polygon) at NBAFS (51.7 ± 14.7 ha) was similar to that reported in other parts of the species’ range. Radiotracked snakes exhibited different patterns of resource use at different spatial scales. At the landscape scale (selection of locations within the landscape), snakes overutilized old-field and forest edge habitats and underutilized forested habitats and wetlands relative to availability. At this scale, snakes also overutilized areas containing sandy loam soils and areas with lower slope (mean slope = 5.2% at snake locations vs. 6.7% at random locations). We failed to detect some of these patterns of resource use at the home range scale (i.e., within the home range). Our ability to detect resource selection by the snakes only at the landscape scale is likely the result of greater heterogeneity in macrohabitat features at the broader landscape scale. From a management perspective, future studies of habitat selection for rare species should include measurement of available habitat at spatial scales larger than the home range. We suggest that the maintenance of open early successional habitats as a component of forested landscapes will be critical for the persistence of eastern hognose snake populations in the northeastern United States.     

A mitogenomic study on the phylogenetic position of snakes

Phylogenetic relationships of squamates (lizards, amphisbaenians and snakes) have received considerable attention, although no consensus has been reached concerning some basal divergences. This paper focuses on the Serpentes (snakes), whose phylogenetic position within the Squamata remains uncertain despite a number of morphological and molecular studies. Some mitogenomic studies have suggested a sister-group relationship between snakes and varanid lizards, while other studies have identified snakes and lizards as sister groups. However, recent studies using nuclear data have presented a different scenario, with snakes being more closely related to anguimorph and iguanian lizards. In this mitogenomic study we have examined the above hypotheses with the inclusion of amphisbaenians, one gekkotan and one acrodont lizard, taxa not represented in previous mitogenomic studies. To this end we have also extended the representation of snakes by sequencing five additional snake genomes: two scolecophidians ( Ramphotyphlops australis and Typhlops mirus ) two henophidians ( Eunectes notaeus and Boa constrictor ) and one caenophidian ( Elaphe guttata ). The phylogenetic analysis recovered snakes and amphisbaenians as sister groups, thereby differing from previous hypotheses. In addition to a discussion on previous morphological and molecular studies in light of the results presented here, the current study also provides some details regarding features of the new snake mitochondrial genomes described.     

Rapid increase in snake dietary diversity and complexity following the end-Cretaceous mass extinction

The Cenozoic marked a period of dramatic ecological opportunity in Earth history due to the extinction of non-avian dinosaurs as well as to long-term physiographic changes that created new biogeographic theaters and new habitats. Snakes underwent massive ecological diversification during this period, repeatedly evolving novel dietary adaptations and prey preferences. The evolutionary tempo and mode of these trophic ecological changes remain virtually unknown, especially compared with co-radiating lineages of birds and mammals that are simultaneously predators and prey of snakes. Here, we assemble a dataset on snake diets (34,060 observations on the diets of 882 species) to investigate the history and dynamics of the multidimensional trophic niche during the global radiation of snakes. Our results show that per-lineage dietary niche breadths remained remarkably constant even as snakes diversified to occupy disparate outposts of dietary ecospace. Rapid increases in dietary diversity and complexity occurred in the early Cenozoic, and the overall rate of ecospace expansion has slowed through time, suggesting a potential response to ecological opportunity in the wake of the end-Cretaceous mass extinction. Explosive bursts of trophic innovation followed colonization of the Nearctic and Neotropical realms by a group of snakes that today comprises a majority of living snake diversity. Our results indicate that repeated transformational shifts in dietary ecology are important drivers of adaptive radiation in snakes and provide a framework for analyzing and visualizing the evolution of complex ecological phenotypes on phylogenetic trees.

The Cenozoic marked a period of dramatic ecological opportunity in Earth history due to the extinction of non-avian dinosaurs and long-term physiographic changes. This phylogenetic natural history study offers new insights into the evolution of snake ecological diversity after the end-Cretaceous mass extinction, as they took advantage of these new opportunities.     

Phylogeography of the Ibero-Maghrebian red-eyed grass snake (<Emphasis Type="Italic">Natrix astreptophora</Emphasis>)

We examined phylogeographic differentiation of the red-eyed grass snake (Natrix astreptophora) using 1984 bp of mtDNA and 13 microsatellite loci from specimens collected across its distribution range in southwestern Europe and northwestern Africa. Based on phylogenetic analyses of mtDNA, European N. astreptophora constituted the sister clade to a weakly supported North African clade comprised of two deeply divergent and well-supported clades, one corresponding to Moroccan snakes and the other to snakes from Algeria and Tunisia. This tripartite differentiation was confirmed by analyses of microsatellite loci. According to a fossil-calibrated molecular clock, European and North African N. astreptophora diverged 5.44 million years ago (mya), and the two Maghrebian clades split 4.64 mya. These dates suggest that the radiation of the three clades was initiated by the environmental changes related to the Messinian Salinity Crisis and the reflooding of the Mediterranean Basin. The differentiation of N. astreptophora, with distinct clades in the Iberian Peninsula and in the western and eastern Maghreb, corresponds to a general phylogeographic paradigm and resembles the differentiation found in another co-distributed Natrix species, the viperine snake (N. maura). Despite both species being good swimmers, the Strait of Gibraltar constitutes a significant biogeographic barrier for them. The discovery that North Africa harbours two endemic lineages of N. astreptophora necessitates more conservation efforts for these imperilled snakes.     

Feeding Strategies in Marine Snakes: An Analysis of Evolutionary, Morphological, Behavioral and Ecological Relationships

Analysis of 1,063 stomach contents from 39 species of sea snakesindicates that about one-third of the shallow, warm, marine,Indo-Australian fish families are preyed upon by sea snakes.Families of eels and gobies are taken by the greatest numbersof snake species. Most species of sea snakes feed on fish familieswhose members are relatively sedentary, dwelling along the bottom,within burrows or reef crevices. With one exception, a fishegg-eating specialization found uniquely in the Aipysurus-Emydocephaluslineage, the dietary habits of sea snakes cannot be categorizedaccording to the snakes' three phylogenetic lineages. Eels,mullet-like, rabbitfish-like and goby-like fish forms are takenby all three lineages. Two or three snake species are generalists,and numerous ones specialize on eels, goby-like fish or catfish.There are differences among sea snake species in the relationshipbetween snake neck girth and the maximum diameter of the prey;in the relationships of both snake gape measurements and fanglength, to the type of prey taken; and in the relationship ofsnake shape and body proportions to the prey selected. Severalmodes of feeding have been observed among sea snakes: feedingin nooks and crannies in the bottom or in reefs, cruising nearthe bottom, and feeding in drift lines. Analysis of percentdigestion of stomach contents and projections backward to thetimes of prey capture provides evidence for feeding periodicity.The greatest amount of diet overlap is for two species of seasnakes which do not both occur at the same locality. Where speciesdo co-occur, diet overlap index values are lower. The numbersof species present as well as their relative abundances varyamong localities as does the relative importance of generalists,eel-eaters, egg-eaters and other specialized feeders.     

Body size as a primary determinant of ecomorphological diversification and the evolution of mimicry in the lampropeltinine snakes (Serpentes: Colubridae)

Evolutionary correlations between functionally related character suites are expected as a consequence of coadaptation due to physiological relationships between traits. However, significant correlations may also exist between putatively unrelated characters due to shared relationships between those traits and underlying variables, such as body size. Although such patterns are often dismissed as simple body size scaling, this presumption may overlook important evolutionary patterns of diversification. If body size is the primary determinant of potential diversity in multiple unrelated characters, the observed differentiation of species may be governed by variability in body size, and any biotic or abiotic constraints on the diversification thereof. Here, we demonstrate that traits related to both predatory specialization (gape and diet preference) and predatory avoidance (the development of Batesian mimicry) are phylogenetically correlated in the North American snake tribe Lampropeltini. This is apparently due to shared relationships between those traits and adult body size, suggesting that size is the primary determinant of ecomorphological differentiation in the lampropeltinines. Diversification in body size is apparently not linked to climatic or environmental factors, and may have been driven by interspecific interactions such as competition. Additionally, we find the presence of a ‘key zone’ for the development of both rattle‐ and coral snake mimicry; only small snakes feeding primarily on ectothermic prey develop mimetic colour patterns, in or near the range of venomous model species.     

Diverse Evidence for the Decline of an Adaptation in a Coral Snake Mimic

Losses of adaptations in response to changed selective pressures are evolutionarily important phenomena but relatively few empirical examples have been investigated in detail. To help fill this gap, we took advantage of a natural experiment in which coral snake mimics occur on two nearby tropical islands, one that has coral snake models (Trinidad) and one that lacks them (Tobago). On Tobago, an endemic coral snake mimic (Erythrolamprus ocellatus) exists but has a relatively poor resemblance to coral snakes. Quantitative image analysis of museum specimens confirmed that E. ocellatus is a poor mimic of coral snakes. To address questions related to the functional importance of this phenotype, we conducted a field experiment on both islands with snake replicas made of clay. These results clearly indicated a strong inter-island difference in predator attack rates where snake replicas that resembled coral snakes received protection in Trinidad but not in Tobago. Further, a molecular phylogenetic analysis of the ancestry of E. ocellatus revealed that this poor coral snake mimic is deeply nested in a clade of good coral snake mimics. These data suggest that the lack of coral snakes on Tobago altered the selective environment such that the coral snake mimicry adaptation was no longer advantageous. The failure to maintain this ancestral feature in allopatry provides a compelling example of how losses of complex adaptations can occur.     

Estimated number of snake species that can be managed by Species Survival Plans in North America

A survey designed to estimate the number of snake enclosures available for Species Survival Plan (SSP) programs was distributed to all North American zoos containing 100 or more reptile and amphibian specimens. Of the 52 zoos surveyed, 44 (84.6%) responded, indicating that 790 (26.3%) of the 3,012 snake enclosures were available for SSP programs. Available enclosures were classified by size and existing themes to help define limitations of the potential SSP space. This spatial information was then used in conjunction with existing population genetics models to estimate that up to 16 snake species can be accommodated by SSP programs in these zoos collectively. Values used in the models were estimates of those for an average snake species with a generation time of 15 years, lambda of 1.15, with 26 effective founders, and an n_e/n ratio of 0.3. It was further assumed that 90% of the genetic variation would be maintained in each species for a period of 100 years. Tactics to increase the number of species that SSP programs can accommodate include: increase reserve space, devote more space for SSP snakes, lengthen generation time, promote gene exchange with wild populations, goal SSP programs for less than 200 years, invest in short-term programs, involve the private sector, build new enclosures, increase the number of snakes per enclosure, and encourage participation of non-North American institutions. To maximize biological diversity in relation to captive carrying capacity, it is recommended that SSP programs represent both infraorders of living snakes and as many families within those infraorders as possible. Although not all 16 families of snakes are likely to be represented due to exhibit value, obtainability, and husbandry success, it may be possible to represent as many as nine families in 16 SSP programs. © 1993 Wiley-Liss, Inc.