No abstract

Many animal populations that are endangered in mainland areas exist in stable island populations, which have the potential to act as an ''ark'' in case of mainland population declines. Previous studies have found neutral genetic variation in such species to be up to an order of magnitude lower in island compared to mainland populations. If low genetic variation is prevalent across fitnessrelated loci, this would reduce the effectiveness of island populations as a source of individuals to supplement declining mainland populations or re-establish extinct mainland populations. One such species, the black-footed rock-wallaby (Petrogale lateralis lateralis), exists within fragmented mainland populations and small island populations off Western Australia. We examined sequence variation in this species within a fitness-related locus under positive selection, the MHC class II DAB b1 locus. 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, in concordance with results from microsatellites (genotyped in a previous study), but preserved unique alleles which were not found in mainland populations. Where possible, conservation actions should pool individuals from multiple populations, not only island populations, for translocation programs, and focus on preventing further declines in mainland populations.

Although the theoretical effects of a severe reduction in effective population size (i.e. a bottleneck) are well known, relatively few empirical studies of bottlenecks have been based on extensive temporally spaced samples of a population both before and after a bottleneck. Here we describe the results of one such study, utilising the Jenolan Caves (JC) population of the brush-tailed rock-wallaby (Petrogale penicillata). When first sampled in 1985 (n = 20) the JC population comprised ~90 individuals. Subsequently the population crashed, and by 1992 only seven individuals remained. In 1996 the entire population (n = 10) was again sampled. Genetic diversity in the pre- and post-crash JC population was compared using 11 polymorphic microsatellite loci and PCR–SSCP analysis of the mitochondrial DNA control region. Only a single unique control region haplotype was detected in the pre- and post-crash JC population, although variant haplotypes were present in other P. penicillata populations. Of the 35 microsatellite alleles present in the pre-crash population, nine (26%) were lost during the bottleneck. The average number of rare alleles declined by 72%, allelic diversity was reduced by 30% and average heterozygosity declined by 10%. These observations are consistent with theoretical predictions. Additional analyses revealed that a P.�penicillata female at Wombeyan Caves was the only survivor of a 1990/91 reintroduction attempt using animals from JC. Of the microsatellite alleles detected in this female, 21% (4/19) were no longer present in the post-crash JC population. Furthermore, the genetic profiles of animals from the recently discovered Taralga population indicate that they are not derived from JC stock, but represent a threatened remnant of a hitherto undetected natural P. penicillata population.

Modern molecular genetic techniques provide a valuable means to address questions concerning the origins of naturalized populations. Brush-tailed rock-wallabies (Petrogale penicillata), of unknown provenance, were introduced to New Zealand from Australia in the early 1870s. While the introduced wallabies prospered in New Zealand, their antecedents in Australia experienced widespread local population extinctions as part of a drastic, widespread and ongoing decline. In this study, a polymerase chain reaction-single-strand conformation polymorphism analysis was undertaken of mitochondrial DNA (mtDNA) control region sequences from P. penicillata in New Zealand (n = 18) and throughout the species' native range in southeastern Australia (n = 54). A single mtDNA haplotype was identified in New Zealand, while 17 haplotypes were found in sampled Australian populations. Phylogenetic analysis (583 bp sequence) revealed the presence of three divergent mtDNA groups within Australian P. penicillata, with each group showing distinct geographical circumscription. The New Zealand haplotype consistently clustered within the central New South Wales group and was most similar (0.55% sequence divergence) to a haplotype from Winmalee, just west of Sydney. It seems likely then, that the New Zealand population of P. penicillata was founded by animals captured near Sydney in the late 19th century. Since P. penicillata in this region have experienced widespread population declines and extinctions, the naturalized New Zealand population represents a potentially valuable conservation resource for Australia. However, the unusual history of New Zealand's P. penicillata presents unique challenges to Australian wildlife managers.