Phylogeography of brushtail possums (Phalangeridae: Trichosurus) reveals higher diversity in Western Australia than previously detected

Australia holds the world record for mammal extinctions, driven primarily by habitat loss and invasive species. Many of these extinct species occupied broad ranges across the continent. One such species that has suffered declines since European colonisation of Australia, despite remaining common in some areas, is the nocturnal, arboreal marsupial, the common brushtail possum (Trichosurus vulpecula). Understanding genetic relationships between populations of common and widespread species is crucial for identifying unique genetic lineages and informing effective conservation strategies to mitigate future declines. Previous genetic studies on brushtail possums have had limited sampling, which has precluded a comprehensive assessment of the relationships within the species and genus. Using both Single Nucleotide Polymorphism markers and mitochondrial DNA (cytochrome b), this study employed phylogenetics, ancestry coefficients using spatially explicit sNMF, and tested genetic differentiation between populations, to examine the phylogeography and population structure of brushtail possums across Australia. Our results indicate that the current subspecies classifications of T. vulpecula do not accurately reflect the genetic structure across Australia. Trichosurus vulpecula hypoleucus, as it is currently defined, includes populations in the Pilbara and Midwest of Western Australia, which our analyses show are genetically similar to southeastern and central T. v. vulpecula. These findings have significant implications for the classification, management, and conservation of brushtail possum taxa, and highlights the importance of comprehensive genetic sampling, particularly in widespread species.