Serpent Research: Relationships between some Old World Rat Snakes resolved

The Old World Rat Snakes have been a source of confusion for many years, they have a diverse morphology and behaviors that have been a puzzle to herpetologists for some time - the kind of puzzle best solved with molecular techniques. The last decade has seen an incredible rise in the use of molecular phylogenies to examine relationships in snakes, assess biogeographic origins, understand processes of adaptive radiation and ultimately correct taxonomy with regard to paraphyletic and polyphyletic groups at multiple levels. The importance of using phylogenetic trees to uncover genealogical relationships and properly construct a taxonomy of organisms cannot be overstated. The development of DNA sequencing technology has increased the available genetic data for phylogenetic inference and the development of model-based statistical methods, such as maximum likelihood and Bayesian inference, which has enhanced the reliability of reconstructed phylogenies. Using molecular data to examine phylogenetic relationships provides evidence to clarify systematic ambiguities from morphological characters and helps avoid misleading relationships due to convergence of morphology. Therefore, an abundance of molecular data with information from independent loci is able to provide strong evidence to assess taxonomic composition and test monophyly.

Using one mitochondrial gene and five nuclear loci, Xin Chen and colleagues (2014) evaluated the taxonomic status of a rare Borneo endemic, the Rainbow Tree Snake Gonyophis margaritatus. The authors inferred a molecular phylogeny of 101 snake species. Both maximum likelihood and time- calibrated Bayesian inference phylogenies demonstrated that G. margaritatus is sister to the Green Trinket Snake, Rhadinophis prasinus of northern Thailand, previously considered to be part of a radiation of Old World ratsnakes. This group is in turn sister to a group containing Rhadinophis frenatus (India, southern China, Taiwan, and North Vietnam) and the Rhinoceros Ratsnake, Rhynchophis boulengeri with the entire clade originating in the mid-Miocene (~16 Ma) in Southeast Asia. This group is sister to the genus Gonyosoma and together originated in the early Miocene (~20 Ma). The authors discuss three potential solutions towards eliminating polyphyly of the genus Rhadinophis, but recommend using the genus name Gonyosoma for all species within this clade, which currently contains all of the species within the genera Gonyosoma, Gonyophis, Rhadinophis, and Rhynchophis.