Phylogeny, evolutionary history, and biogeography of Oriental-Australian rear-fanged water snakes (Colubroidea: Homalopsidae) inferred from mitochondrial and nuclear DNA sequences.

ABSTRACT

Homalopsid snakes are widely distributed throughout Southeast Asia and form the ecologically dominant component of the herpetofauna over much of their range. Although they are considered well differentiated from other colubrid lineages, several aspects of their radiation including within-family relationships, temporal patterns of species diversification, and biogeographic history remain under studied. We analyzed sequence data from four genes (three mitochondrial and one nuclear) for 22 species of the Homalopsidae to generate the most comprehensive phylogeny of the family to date. We also estimated divergence times within the family using a model of independent but log-normally distributed rates of evolution in conjunction with two external fossil calibrations. Using this chronogram, we inferred historical patterns of species diversification within the family. Finally, we used previously published sequence data for 172 snake species to test for the monophyly of the Homalopsidae. Phylogenetic analysis reveals strong support for homalopsid monophyly with an estimate age of the crown group of approximately 22 MYA. The family comprises three major clades which all originated 18-20 MY. Lineage through time plots reveal that homalopsids experienced a significantly higher rate of effective cladogenesis in their early history, consistent with a hypothesis of adaptive radiation. We discuss several Miocene and Pliocene paleogeographic factors that might underlie observed patterns of temporal diversification and biogeography.