Uncovering cryptic evolutionary diversity in extant and extinct populations of the southern Australian arid zone Western and Thick-billed Grasswrens (Passeriformes: Maluridae: Amytornis)

Abstract

The Western and Thick-billed Grasswrens (Aves: Passeriformes: Maluridae:Amytornis textilis and A. modestus, respectively) exemplify issues surrounding the evolution, biogeography and conservation of Australia's arid and semi-arid zone fauna. The two species together have historically occurred across much of southern Australia. They showed high intraspecific taxonomic diversity and short range endemism but suffered high rates of recent anthropogenic extinction. Of 11 named and one un-named subspecies, five are extinct and three are vulnerable or critically endangered. To clarify taxonomic issues, and to understand their pre-extinction phylogeography and identify extant populations and taxa of conservation value, we sequenced ~1000 bp of the mtDNA ND2 gene from all extant populations and all but one extinct population. We confirmed reciprocal monophyly of A. modestus and A. textilis and identified strong phylogeographic structure associated with morphological divergence within each species. Populations of A. t. myall at the western edge of their range in South Australia may preserve “ghost” lineages of extinct subspecies from Western Australia as a result of ancient gene flow. Our results support recent taxonomic revisions, and highlight the critical importance of including samples of extirpated populations and extinct species to fully understand and interpret extant diversity. Conservation and management plans should recognise and seek to preserve the unique evolutionary diversity present in surviving populations.