The findings of a Massey University study that investigated the unrestricted gene ﬂow between two subspecies of translocated brushtail possums are significant to Aotearoa's goal of being predator-free by 2050.
PhD student Nimeshika Pattabiraman and her supervisors Professor Steve Trewick and Professor Mary Morgan-Richards co-wrote the research paper alongside former Department of Conservation scientist Ralph Powlesland.
Despite more than 100 years of potential interbreeding, distinctive characteristics of two brushtail possum subspecies, Trichosurus vulpecula, remain evident. These morphological differences suggest the two main forms are reproductively separate, but the new population genetic data show otherwise.
Trewick says as New Zealand pursues the goal of predator pest eradication, this research is a significant step in understanding the reproductive behaviour of possums and the population's genetic diversity.
"It is common to see black or grey possums that are descendants of the subspecies originally introduced from different parts of Australia. Anecdotal information suggests these different types of brushtail possum have different behaviours, including their responses to traps and poison and that they do not interbreed. If so, this would significantly amplify the difficulty of managing and finally eradicating this pest problem.
"Our analysis of morphological and genetic data indicates that the different colour variants of brushtail possums in Aotearoa are, however, freely interbreeding. This means that fur colour is not an indicator of separate biological lineages, so the pest can be treated as a single species for management."
Each pest species targeted for control or eradication requires a specific strategy, Trewick says.
"Being confident that we are dealing with a single possum type will help in the development and application of eradication for the benefit of biological diversity and ecosystem resilience in Aotearoa."
Along with mustelids (carnivorous mammals such as ferrets) and rats, possums are being targeted by the Predator Free 2050 initiative.
"Possums ravage the native fauna and flora and directly impact biodiversity resilience. They are also transmitters of bovine tuberculosis among agricultural animals," Trewick says.
Brushtail possums were introduced to Aotearoa from Australia in the mid-1800s, with a view to developing a fur trade, but once released the feral population exploded and spread through the country in all types of habitats.
You can read the research paper here.