Dipsas

Abstract: A molecular phylogeny of the Neotropical snail-eating snakes (tribe Dipsadini) is presented including 43 (24 for the first time) of the 77 species, sampled for both nuclear and mitochondrial genes. Morphological and phylogenetic support was found for four new species of Dipsas and one of Sibon, which are described here based on their unique combination of molecular, meristic, and color pattern characteristics. Sibynomorphus is designated as a junior subjective synonym of Dipsas. Dipsas latifrontalis and D. palmeri are resurrected from the synonymy of D. peruana. Dipsas latifasciata is transferred from the synonymy of D. peruana to the synonymy of D. palmeri. A new name, D. jamespetersi, is erected for the taxon currently known as Sibynomorphus petersi. Re-descriptions of D. latifrontalis and D. peruana are presented, as well as the first photographic voucher of an adult specimen of D. latifrontalis, along with photographs of all known Ecuadorian Dipsadini species. The first country record of D. variegata in Ecuador is provided and D. oligozonata removed from the list of Peruvian herpetofauna. With these changes, the number of Dipsadini reported in Ecuador increases to 22, 18 species of Dipsas and four of Sibon.

Abstract: Efficient venom delivery systems are known to occur only in varanoid lizards and advanced colubroidean snakes among squamate reptiles. Although components of these venomous systems might have been present in a common ancestor, the two lineages independently evolved strikingly different venom gland systems. In snakes, venom is produced exclusively by serous glands in the upper jaw. Within the colubroidean radiation, lower jaw seromucous infralabial glands are known only in two distinct lineages–the basal pareatids and the more advanced Neotropical dipsadines known as “goo-eating snakes”. Goo-eaters are a highly diversified, ecologically specialized clade that feeds exclusively on invertebrates (e.g., gastropod molluscs and annelids). Their evolutionary success has been attributed to their peculiar feeding strategies, which remain surprisingly poorly understood. More specifically, it has long been thought that the more derived Dipsadini genera Dipsas and Sibynomorphus use glandular toxins secreted by their infralabial glands to extract snails from their shells. Here, we report the presence in the tribe Dipsadini of a novel lower jaw protein-secreting delivery system effected by a gland that is not functionally related to adjacent teeth, but rather opens loosely on the oral epithelium near the tip of the mandible, suggesting that its secretion is not injected into the prey as a form of envenomation but rather helps control the mucus and assists in the ingestion of their highly viscous preys. A similar protein-secreting system is also present in the goo-eating genus Geophis and may share the same adaptive purpose as that hypothesized for Dipsadini. Our phylogenetic hypothesis suggests that the acquisition of a seromucous infralabial gland represents a uniquely derived trait of the goo-eating clade that evolved independently twice within the group as a functionally complex protein-secreting delivery system. The acquisition by snail-eating snakes of such a complex protein-secreting system suggests that the secretion from the hypertrophied infralabial glands of goo-eating snakes may have a fundamental role in mucus control and prey transport rather than envenomation of prey. Evolution of a functional secretory system that combines a solution for mucus control and transport of viscous preys is here thought to underlie the successful radiation of goo-eating snakes.

Abstract: The name Dipsas variegata (Dumeril, Bibron, and Dumeril) has been applied to snakes disjunctively distributed in northeastern South America and in Panama and western South America. The specific name variegata is here restricted to populations occurring from Venezuela to Trinidad and French Guiana, and seemingly to the mouth of the Amazon in Brazil. Records from Colombia are unsubstantiated. The name Dipsas nicholsi (Dunn) is revalidated for a Central American endemic with an exceptionally small range in central Panama. Specimens from western Ecuador previously assigned to “Dipsas variegata nicholsi” represent a different species—Dipsas andiana (Boulenger), which is resurrected from the synonymy of Dipsas oreas (Cope). Other records of Dipsas variegata from western Ecuador and southeastern Peru are based on misidentifications of species well known from those areas. Dipsas nicholsi and D. andiana differ in some scutellation, hemipenial, and color pattern characters. The two species share an unusual...

Abstract: The Leptodeirini has been presumed to be a monophyletic assemblage based on albumin immunological data and morphology and consisted of neotropical cat-eyed snakes (Leptodeira), blunt-headed vine snakes (Imantodes), nightsnakes (Eridiphas, Hypsiglena, and Pseudoleptodeira), and the cloud forest snake (Cryophis). In the present study, approximately 1.4 kb of mitochondrial DNA sequence data (from cob and nad4) were collected to test the monophyly of the Leptodeirini. These data were analysed using maximum parsimony, maximum likelihood, and Bayesian methods. None of the results supported the monophyly of the Leptodeirini. There was strong support for a clade containing Imantodes and Leptodeira, and another clade containing the nightsnakes, with the latter placed closer to Cryophis and other dipsadine genera (Sibon, Dipsas, and Atractus). This partial reassessment of the Dipsadinae infers the group to have an ancestral condition of being rear-fanged, mildly venomous, and feeding on ectothermal vertebrates, with a more derived radiation that has lost the rear-fanged, venomous condition and has a diet specialized on invertebrates. A brief discussion on the biogeography of the dipsadines shows the group to be much older (Palaeocene), consistent with earlier views, as opposed to a more recent (Miocene) hypothesis, as has been recently suggested. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92, 483–500.