Phylogeography of Australia's king brown snake (Pseudechis australis) reveals Pliocene divergence and Pleistocene dispersal of a top predator

摘要

King brown snakes or mulga snakes (Pseudechis australis) are the largest and among the most dangerous and wide-ranging venomous snakes in Australia and New Guinea. They occur in diverse habitats, are important predators, and exhibit considerable morphological variation. We infer the relationships and historical biogeography of P. australis based on phylogenetic analysis of 1,249 base pairs from the mitochondrial cy-tochrome b, NADH dehydrogenase subunit 4 and three adjacent tRNA genes using Bayesian, maximum-likelihood, and maximum-parsimony methods. All methods reveal deep phylogenetic structure with four strongly supported clades comprising snakes from New Guinea (Ⅰ), localities all over Australia (Ⅱ), the Kimberleys of Western Australia (Ⅲ), and north-central Australia (Ⅳ), suggesting a much more ancient radiation than previously believed. This conclusion is robust to different molecular clock estimations indicating divergence in Pliocene or Late Miocene, after landbridge dispersal to New Guinea had occurred. While members of clades Ⅰ, Ⅲ and Ⅳ are medium-sized, slender snakes, those of clade Ⅱ attain large sizes and a robust build, rendering them top predators in their ecosystems. Genetic differentiation within clade Ⅱ is low and haplotype distribution largely incongruent with geography or colour morphs, suggesting Pleistocene dispersal and recent ecomorph evolution. Significant haplotype diversity exists in clades Ⅲ and Ⅳ, implying that clade Ⅳ comprises two species. Members of clade Ⅱ are broadly sympatric with members of both northern Australian clades. Thus, our data support the recognition of at least five species from within P. australis (auct.) under various criteria. We discuss biogeo-graphical, ecological and medical implications of our findings.