Isolated remnant or recent introduction? Estimating the provenance of Yellingbo leadbeater's possums by genetic analysis and bottleneck simulation.

Effective conservation management requires that genetically divergent populations potentially harbouring important local adaptations be identified and maintained as separate management units. In the case of the endangered Australian Leadbeater's possum (Gymnobelideus leadbeateri), an arboreal marsupial endemic to Victoria, uncertainty over the evolutionary origin of a potentially important extant wild population recently discovered in atypical habitat (lowland swamp) at Yellingbo is hampering such efforts. The population is rumoured to be a recent introduction. Microsatellite allele frequencies at Yellingbo differed substantially from those in sampled populations in montane ash forest (F(ST) between 0.23 and 0.36), and Bayesian clustering analyses of genotypes strongly separated them (K = 2). We conducted a suite of bottlenecking tests which all indicated that Yellingbo had undergone a recent reduction in size. The extent to which the distinctiveness of Yellingbo animals might be expected solely through bottlenecking associated with a recent introduction, was tested by simulating population-history scenarios seeded with genotypes from candidate wild and captive sources. No bottleneck scenario reproduced anything approaching the genetic distinction of the Yellingbo population, with all STRUCTURE analyses placing Yellingbo in a separate cluster to simulated populations (K = 2, minimum F(ST) = 0.13). These results suggest that Yellingbo does not share recent ancestry with other extant populations and instead may be a remnant of an otherwise extinct gene pool. Importantly, this may include genes involved in adaptation to a lowland swamp environment, substantially adding to the conservation importance of this population, and suggesting that separate management may be prudent until evidence suggests otherwise.