The black-footed rock-wallaby (Petrogale lateralis lateralis) population on Barrow Island contains one of the lowest levels of genetic diversity of any mammal. In contrast, mainland black-footed rock-wallaby populations in the wheat-belt and Exmouth regions of Western Australia contain relatively healthy levels of genetic diversity, despite having suffered recent population bottlenecks due to fox predation. These measures of diversity were performed with microsatellites, a non-functional and selectively neutral class of genetic markers.
To find out whether these results may also apply to functional genes that have a bearing on the fitness of individuals and populations, we examined levels of diversity at an immune system antigen recognition gene (DAB β1) in island and mainland populations of the black-footed rock-wallaby. The mainland populations displayed greater levels of allelic diversity (4–7 alleles) than the island population, despite being small and isolated, and contained at least two DAB gene copies. The island population displayed low allelic diversity (2 alleles) and fewer alleles per individual in comparison to mainland populations, and probably possesses only one DAB gene copy.
The patterns of DAB diversity suggested that the island population has a markedly lower level of genetic variation than the mainland populations, but preserves unique alleles not found in mainland populations. If this result reflects the patterns of other immune genes, the island population would be highly susceptible to infections. Where possible, conservation programs should pool individuals from multiple populations, not only island populations, for translocation events, and focus on preventing further declines in mainland populations.