Analysis of mitochondrial control region DNA variation in New Zealand's brushtail possums (Trichosurus vulpecula) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Ecology at Massey University

Abstract

Brushtail possums (Trichosurus vulpecula) were first introduced from Australia to New Zealand in 1858 to establish a fur industry. Currently numbering more than 65 million, they are recognised as the most important mammalian pest in New Zealand, because of the environmental and agricultural damage they cause. Possums act as a wildlife reservoir of bovine tuberculosis (Tb) and, as such, threaten New Zealand's multi-million dollar beef and dairy industry. Eliminating bovine Tb in livestock requires removal of contact with infected possums. This is mainly achieved through the intensive poisoning of areas of known wildlife Tb infection and the establishment around them of zones of low possum density (known as buffer zones) adjacent to at-risk farmland. Not only does this result in lower possum density, and thus fewer dispersing possums, but may also affect the movement patterns of possums. Measurement of gene frequency differences between populations associated with a buffer zone would allow a qualitative estimate of the effect of buffer zones on limiting possum movement. The mitochondrial DNA (mtDNA) control region is an effective marker for detecting intraspccific genetic structure because it has a high mutation rate, lack of recombination and uniparental mode of inheritance. An extensive survey of brushtail possum mtDNA control region variation in New Zealand was conducted to quantify levels of variation and thus assess the utility of the mtDNA control region as a marker for detecting genetic differentiation between possum populations. Nine haplotypes were found among 70 possums from throughout New Zealand. Most of the variation (six haplotypes) was concentrated in the North Island, and the most widespread haplotype (occurring in all four islands surveyed) was also the most common - found in 67% of possums surveyed. The technique of single stranded conformation polymorphism (SSCP) was developed for the brushtail possum so that a quick, cost-effective and sensitive method for surveying mtDNA control region variation in large numbers of individuals was available. This assay was applied to screen the variation in possums separated by small spatial scales associated with two buffer zones in the South Island. A total of 234 possums were screened, with 98.7% found to possess the same haplotype. The other 1.3%, all from one location, possessed a second haplotype. The extremely low levels of variation makes it highly unlikely that surveys of variation in mtDNA will be able to detect an effect of buffer zones on possum movement, at least in the South Island. Areas of higher variation, such as certain parts on the North Island, would be better candidates for testing the effect of barriers such as buffer zones on genetic differentiation between possum populations.