Origins and diversity of invasive brushtail possums ( <i>Trichosurus vulpecula</i> ) in New Zealand surveyed with mtDNA haplotype and nuclear microsatellite data

ABSTRACT The brushtail possum Trichosurus vulpecula is native to Australia where six subspecies exist in distinct regions. A composite invasive population is established in Aotearoa New Zealand, which has since been subject to localised bouts of culling. We surveyed population genetic structure across New Zealand to identify the scale of genetic diversity introduced to New Zealand and the resulting pattern of admixture. Australian brushtail possums have high mitochondrial diversity (17%) and prominent spatial structure. Thirty‐eight haplotypes among 25 New Zealand population samples (n = 465) were closely related to 45 haplotypes sampled from Victoria and Tasmania in Australia (n = 120), but just one was shared. High haplotype diversity is consistent with multiple successful introductions and rapid population expansion in New Zealand. Nuclear diversity of microsatellite loci screened in 18 New Zealand population samples (n = 374) comprised five genotypic clusters (K = 5), but these groups did not correlate with geography. An overall signal of genetic partitioning within the invasive population suggests limited mixing but ongoing management towards eradication will influence patterns of population recovery, migration and evolution of traits including toxin resistance. We consider the implications of mixed ancestry of the invasive population in terms of variation in toxin tolerance detected in New Zealand.