Molecular phylogeny of the Australian venomous snake genus Hoplocephalus (Serpentes, Elapidae) and conservation genetics of the threatened H. stephensii

Abstract

The Australian elapid snake Hoplocephalus stephensii (Stephens' Banded Snake) is patchily distributed in disjunct forest remnants in eastern Australia and is listed as threatened in both states in which it occurs (Qld and NSW). Here we focus on the phylogeography of H. stephensii to address (1) the genetic distinctiveness of this taxon within its genus and (2) the level of genetic diversity present within and between disjunct populations from throughout the species' range. We sequenced an approximately 900 base pair DNA fragment of the mitochondrial genome that includes half of the ND4 gene and three tRNA genes. We obtained sequence data from 15 H. stephensii individuals drawn from four populations, plus representatives of the other Hoplocephalus species. Phylogenetic analyses of the data produced a single fully resolved tree. The two coastal taxa (H. bungaroides and H. stephensii) are very closely related (2.6-3.1% sequence divergence) whereas the inland taxon H. bitorquatus is more distantly related to the other two (7.6% vs H. bungaroides; 7.8-8.3% vs H. stephensii). Genetic diversity is low within H. stephensii (nine mitochondrial haplotypes with 1-3 haplotypes with only single base pair differences within populations). The largest split (1.7% sequence divergence) occurs between the northern population and the three southern populations and corresponds to the species distribution north and south of the McPherson Range on the Queensland-New South Wales border. The three southern populations display much less molecular divergence (maximum of 0.6% sequence divergence), consistent with the presence of generally continuous forest throughout the species' range until European invasion of Australia 200 years ago, and with radiotelemetric studies that have found high vagility in these arboreal snakes. Thus, on the basis of genetic distinctiveness we argue that (1) Hoplocephalus bitorquatus should receive high conservation priority; and (2) managers should treat the Queensland and NSW populations of H. stephensi as separate conservation units.