Female dispersal and relatedness structure in common wombats (Vombatus ursinus)

Dispersal patterns were investigated in the common wombat Vombatus ursinus using microsatellite genetic data collected from three study sites. Two of these were within large, high-density populations in Victoria, south-eastern Australia, while the third was a small, isolated population in South Australia. Genetic assignment tests revealed that in the continuous populations, females were more likely to be immigrants into the sampling areas than were males, who were more likely to have been born locally. No such difference between the sexes was detected for the isolated population. At all three sites, pairwise relatedness estimates for males were negatively correlated with geographic distance, suggesting related males were clustered. This pattern was not observed among females, other than in the isolated population, where pairs of females showed a weak decline of relatedness with increasing geographic distance over a large spatial scale. Taken together, these data provide strong evidence that dispersal is predominantly by females. Furthermore, the observed spatial structure of relatedness suggests female breeding dispersal a rare finding among mammalian species. Genetic variation within the isolated population was significantly reduced compared to the sites in Victoria. Our data are not sufficient to distinguish between two possible causes for this: (1) long-term small size and isolation of populations at the edge of the species' range where resources may be more patchily distributed; (2) a genetic bottleneck effect of recent isolation resulting from agricultural development.