Timing of a mtDNA gene rearrangement and intercontinental dispersal of varanid lizards

The mitochondrial genomes of the Komodo monitor (Varanus komodoensis) and the Nile monitor (V. niloticus) were previously shown to have an extensive gene rearrangement. Here, we show that this gene arrangement widely occurs in varanid taxa originated from Africa, Asia and Australasia. Based on phylogenetic relationships of the varanids constructed using mitochondrial DNA sequences encoding the NADH dehydrogenase subunit 2 gene and seven flanking tRNA genes, we estimated their divergence times by the Bayesian method without assuming the molecular clock. The results suggested that the mitochondrial DNA gene rearrangement took place once in an ancestral varanid lineage in the Paleocene or earlier. Our results are more consistent with Cenozoic over-water dispersal of Southeast Asian varanids across the Indonesian Archipelago rather than the Cretaceous Gondwanan vicariance for the origin of Australasian varanids.