Molecular and morphological assessment of Australia’s most endangered snake, Hoplocephalus bungaroides, reveals two evolutionarily significant units for conservation

Abstract

The Broad-headed snake Hoplocephalus bungaroides is one of Australia's most endangered verte- brates. Extant populations of H. bungaroides are restricted to several geographically isolated reserves to the north, west, and south of Sydney. We analysed mitochondrial DNA from 184 specimens drawn from across the geo- graphic range of the Broad-headed snake. Phylogenetic analysis demonstrated that H. bungaroides comprises two divergent mitochondrial lineages with a ''northern'' clade comprising populations west and north of Sydney and a ''southern'' clade comprising animals in Morton National Park. The two clades differ by an uncorrected genetic distance of 1.7%, which implies a divergence dating to approximately 755,000-850,000 years ago. We comple- mented our molecular data set with a detailed analysis of morphological variation both between and within the genetic clades. The two H. bungaroides genetic clades are morphologically indistinguishable and show little sexual dimorphism. Our results demonstrate that the populations north and south of this biogeographic split function as two distinct populations with no recent gene flow. There is no reason for separate taxonomic recognition of these two clades, but they do represent distinct evolutionarily sig- nificant units (ESUs) that require separate conservation management. In addition, within the northern ESU, popu- lations from Royal National Park, Blue Mountains National Park, Wollemi National Park, and the Sydney Water Catchment supply areas should be considered as separate management units to conserve both evolutionary and eco- logical processes.