Genetic analysis of the mating system of the common brushtail possum (Trichosurus vulpecula) in New Zealand farmland

We examined male reproductive success in a common brushtail possum populati on in New Zealand farmland. Paternity was assigned to 66 of 91 pouch young (maternity known), using a likelihood approach applied to genotypes at six microsatellite loci having an overall average exclusion probability of arou nd 99%. The distribution of number of offspring per male was L-shaped with a standardized variance of 1.52. At least 46% of the 76 sampled reproductiv ely mature males, bred, siring between one and four offspring each. Althoug h breeding males were on average older and larger than nonbreeding males, t he small differences did not result in a significant overall difference bet ween the two groups in a multivariate permutation test analagous to a t-tes t. Paternity analysis of 22 sibling pairs (resulting from experimental remo val of pouch young early in the breeding season, inducing a second oestrous ) suggested that sequential mating of females with the same male was uncomm on (approximate to 16-27%). Whilst there was a tendency for female possums to mate with nearby males, consistent with previous observations of territo rial mating behaviour in Australian populations, some interhabitat matings were also inferred. The study population displayed only a low degree of pol ygyny, which may in part reflect population and habitat characteristics of the study site. A comprehensive understanding of the mating system of Trich osurus vulpecula awaits genetic paternity analysis in additional population s from both Australia and New Zealand, using quantitative approaches undert aken in this study.