Population genetics and genomics of a marsupial species : analysis of native and invasive brushtail possum populations (Trichosurus vulpecula) : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Conservation Biology, Massey University, Manawatū Campus, New Zealand
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2024-04-15
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Masey University
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Abstract
One of the leading causes of global biodiversity decline is the introduction of invasive pest species that destroy native flora and compete with native fauna for food and other resources. Aotearoa New Zealand is one of the foremost countries in the world that has focussed on eradicating pest species and in particular exotic mammals from the archipelago, which lacks native, terrestrial mammals. The New Zealand Government recently set in train the ambitious task of removing all mustelids, rats, and possums from the terrestrial landscape by the year 2050. Brushtail possums (Trichosurus vulpecula) were introduced to Aotearoa New Zealand from Australia in the mid-1800s, after which they were translocated across the country and have become widespread, destroying indigenous habitat, eating native birds and invertebrates, and spreading bovine TB.
Control efforts have seen possum numbers decline in the last two decades from close to 75 million in 2002 to 40 million in 2020. There is, however, a gap in the scientific understanding of possum populations with respect to their genetic composition and population structure across the country, and this knowledge could help us develop effective and dynamic management strategies to eradicate possums on a nationwide scale.
In this thesis, I focus on three aspects of population structure and diversity of brushtail possums. First, I investigated a small geographical study area - The Kenepuru Peninsula - where I sought evidence of genetic correlations with geography, time and fur colour. I used two types of genetic markers that target the nuclear and mitochondrial regions of possum DNA with large population samples. In every case, it was determined that the possums comprised one freely interbreeding population at this scale. In particular I demonstrated that colour morphs associated with distinct subspecies in Australia, freely interbreed in New Zealand. I then increased the scale of sampling to include representation of populations across New Zealand and Australia, with the same genetic markers. This threw light on the heterogenous nature of possum diversity in New Zealand, and showed that even after ~110 generations, possums retained genetic separation among spatial groups. Additionally, the data showed evidence of multiple possum lineages across New Zealand that are derived from several Australian populations. High haplotype diversity in New Zealand suggests that the rapidly expanding population has retained novel haplotypes and the data thus far indicated a non-homogenous (metapopulation) distribution of possums without geographical concordance. As the project progressed, I was able to apply high-throughput genotyping-by-sequencing to generate a large genomic dataset. This dataset provided much more detail of the genotypic distribution of possums in Australia and among invasive metapopulations in New Zealand, as well as informing us of the relationship between them. This large, robust database of possum population structure and genetic diversity throughout Aotearoa New Zealand will support future studies in providing informed management decisions to eradicate brushtail possums.
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Trichosurus vulpecula, New Zealand, Molecular genetics, Dispersal, Mitochondrial DNA, Analysis, Population genetics, population genomics, invasive species, microsatellite, mtDNA, genotyping-by-sequencing (GBS), brushtail possums