Genetic diversity in remnant mainland and "pristine" island populations of three endemic Australian macropodids (Marsupialia):Macropus eugenii, Lagorchestes hirsutus and Petrogale lateralis

Since European settlement, mainland Australia has experienced a wave of mammal extinctions and population declines. However, some species have persisted on off-shore islands, which are now viewed as important wildlife refuges. In this study, we assessed the level of genetic diversity, at 7-11 microsatellite loci, in island and remnant mainland populations of three endemic species of macropodid marsupial; the tammar wallaby Macropus eugenii (n = 92); rufous hare-wallaby Lagorchestes hirsutus (n = 40) and black-footed rock-wallaby Petrogale lateralis (n = 164). There was a consistent pattern of significantly higher levels of microsatellite diversity in the remnant mainland population (A = 4.9-13.9; He = 0.61-0.86) of each species compared to conspecific "pristine" island populations (A = 1.2-3.7; He = 0.05-0.44). These marked differences are even apparent where island populations currently have a substantially larger census size. In addition, island populations were substantially inbred (Fe = 0.49-0.91). Although island populations have been insulated from the relatively recent threatening processes operating on the mainland, they have nevertheless been significantly impacted by increased inbreeding and the substantial erosion of genetic diversity. Despite the difficulties of ensuring the survival of remnant mainland populations, they appear to retain substantially more genetic diversity than their island counterparts and therefore are more likely to contribute to the long-term persistence of their species. These data also demonstrate that small remnant mainland populations (n < 10-20) are often capable of rapid recovery and are not necessarily genetically depauperate.