Biogeographic origins of goannas (Varanidae): a molecular perspective.

This project aims to clarify the phylogenetic relationships among the extant species of Varanus in order to elucidate the origins of Varanidae, using DNA sequences. Results obtained for a minimum of 662 nucleotides of 12S rRNA sequence data from each of 21 extant species of Varanus indicate that the Australian varanids form a single monophyletic clade and also suggest that within the Australian varanids, members of the subgenus Odatria (pygmy monitors) may from a clade separate from those in the subgenus Varanus (large monitors). The Asian species appear to be sister taxa to the Australian species, while the two African species investigated were most divergent, suggesting that the Varanidae are not Gondwanic in origin. Hypothesis testing analyses were performed and involved constraining the 12S sequence data according to previously described topologies and testing the difference using parametric and nonparametric statistics. The phylogeny generated using 12S sequence data was statistically different from previously described morphological trees, while there was some support for topologies based on chomosomal and immunological datasets. Overall, our results suggest that the Australian species may be derived from an Asian source and are, therefore, in agreement with the hypothesis based on the fossil record suggesting that Varanidae may be Asian in origin.