Substantial genetic substructuring in southeastern and alpine Australia revealed by molecular phylogeography of the Egernia whitii (Lacertilia: Scincidae) species group

Abstract

Palaeoclimatic events and biogeographical processes since the mid-Tertiary are believed to have strongly influenced the evolution and distribution of the terrestrial vertebrate fauna of southeastern Australia. We examined the phylogeography of the temperate-adapted members of the Egernia whitii species group, a group of skinks that comprise both widespread low- to mid-elevation (E. whitii) and montane-restricted species (Egernia guthega, Egernia montana), in order to obtain important insights into the influence of past biogeographical processes on the herpetofauna of southeastern Australia. Sequence data were obtained from all six temperate-adapted species within the E. whitii species group, and specifically from across the distributional ranges of E. whitii, E. guthega and E. montana. We targeted a fragment of the ND4 mitochondrial gene (696 bp) and analysed the data using maximum likelihood and Bayesian methods. Our data reveal a deep phylogeographical break in the east Gippsland region of Victoria between 'northern' (Queensland, New South Wales, Australian Capital Territory) and 'southern' (Victoria, Tasmania, South Australia) populations of E. whitii. This divergence appears to have occurred during the late Miocene-Pliocene, with the Gippsland basin possibly forming a geographical barrier to dispersal. Substantial structuring within both the 'northern' and the 'southern' clades is consistent with the effects of Plio-Pleistocene glacial-interglacial cycles. Pleistocene glacial cycles also appear to have shaped the phylogeographical patterns observed in the alpine species, E. guthega and E. montana. We used our results to examine the biogeographical process that led to the origin and subsequent diversification of the lowland and alpine herpetofauna of southeastern Australia.