Plio-Pleistocene diversification and genetic population structure of an endangered lizard (the Blue Mountains water skink, Eulamprus leuraensis) in south-eastern Australia

Aim: Although climatic fluctuations occurred world-wide during the Pleistocene, the severity of glacial and drought events - and hence their influence on animal and plant biogeography - differed among regions. Many Holarctic species were forced to warmer-climate refugia during glacial periods, leaving the genetic signature of recent expansion and gene flow among modern-day populations. Montane south-eastern Australia experienced less extreme glaciation, but the effects of drier and colder climatic conditions over this period on biotic distributions, and hence on the present-day genetic structure of animal and plant populations, are poorly known. Location: South-eastern Australia. Methods: The endangered Blue Mountains water skink (Eulamprus leuraensis) is a viviparous lizard known from fewer than 40 isolated small swamps at 560-1060 m elevation in south-eastern Australia. We conducted molecular phylogenetic, dating and population genetics analyses using the mitochondrial NADH dehydrogenase 4 (ND4) of 224 individuals of E. leuraensis sampled across the species' distribution. Results: Ancient divergences in haplotype groups between lizards from the Blue Mountains and the Newnes Plateau, and strong genetic differences, even between swamps separated by only a few kilometres, suggest that the species has persisted as a series of relatively isolated populations within its current distribution for about a million years. Presumably, habitat patches similar to current-day swamps persisted throughout glacial-interglacial cycles in this region, allowing the development of high levels of genetic structuring within and among present-day populations. Main conclusions: Our results suggest that less extreme glacial conditions occurred in the Southern Hemisphere compared with the Northern Hemisphere, allowing cold-adapted species (such as E. leuraensis) to persist in montane areas. However, additional studies are needed before we can assemble a comprehensive view of the impact of Pleistocene climatic variation on the phylogeography of Southern Hemisphere taxa.