Phylogeny and biogeography of the Enhydris clade (Serpentes: Homalopsidae)

Previous molecular phylogenetic hypotheses for the Homalopsidae, the Oriental-Australian Rear-fanged Water Snakes indicate that Enhydris, the most speciose genus in the Homalopsidae (22 of 37 species), is polyphyletic and may consist of five separate lineages. We expand on earlier phylogenetic hypotheses using three mitochondrial fragments and one nuclear gene, previously shown to be rapidly evolving in snakes, to determine relationships among six closely related species: Enhydris enhydris, E. subtaeniata, E. chinensis, E. innominata, E. jagorii, and E. longicauda. Four of these species (E. subtaeniata, E. innominata, E. jagorii, and E. longicauda) are restricted to river basins in Indochina, while E. chinensis is found in southern China and E. enhydris is widely distributed from India across Southeast Asia. Our phylogenetic analyses indicate that these species are monophyletic and we recognize this clade as the Enhydris clade sensu stricto for nomenclatural reasons. Our analysis shows that E. chinensis is sister-species to a well-supported clade comprising the remaining species of the Enhydris clade (mean p distance between E. chinensis and other in-group taxa was 13.1%, range: 12.7-13.4%). Enhydris innominata, E. longicauda and E. jagorii also formed a strongly supported clade with very low interspecific p distances (mean 0.28%, range: 0–0.46%). We were unable to resolve relationships between E. enhydris and E. subtaeniata (mean divergence of 9.4%, range: 9.2-9.7%), and between these two species and E. innominata, E. longicauda and E. jagorii. We summarize classical morphological (scalation and coloration) characteristics of these species in the context of the molecular phylogeny. The Enhydris clade comprises a substantial portion of the vertebrate biomass of Southeast Asia and we discuss aspects of its biogeography, morphology and systematics.