Dispersal patterns and population structure in a small marsupial, Antechinus agilis, from two forests analysed using microsatellite markers

Juvenile male agile antechinus (Antechinus agilis) are thought to disperse immediately after they leave the nest, whereas females are philopatric. However, no genetic data are available to support a hypothesis of male-biased dispersal, and the possible effects of habitat characteristics on dispersal are not known. We used five microsatellite loci to describe the dispersal patterns and population structure of A. agilis at two different forested sites (Mt Donna Buang and Mt Disappointment in central Victoria, south-eastern Australia). Within each site, DNA samples were collected from individuals from different trapping grids (four grids in Mt Donna Buang, collected over two years, and seven grids at Mt Disappointment, collected over one year). To assess levels of genetic structuring among the populations, F_st values (the proportion of genetic variance among populations) were calculated for each site and sex separately, and a test for isolation by distance was performed. Overall, F_st values were low, and did not increase with distance, and this may be the result of high levels of gene flow for both sexes at both sites, at least on the scale of less than 10 km. To investigate microsatellite patterns at a finer scale, we calculated pair-wise relatedness values separately for sites, years and sexes. By comparing these values for animals within and between grids, evidence was found for male-biased dispersal. A genetic assignment test provided further evidence for this: males were more likely to be assigned to grids other than their capture site. Most females had high assignment values for their capture site, although some of the females may have been immigrants. This result could be due to inaccuracies in the assignment test, or due to a higher frequency of dispersal of females than previously thought. The sex-biased dispersal was less pronounced at Mt Disappointment than at Mt Donna Buang. This may be related to the level of disturbance: logging patches, roads and fire-breaks (grass strips) disrupt the forest at Mt Disappointment more than at Mt Donna Buang.