GENETIC POPULATION-STRUCTURE OF THE GREATER BILBY MACROTIS-LAGOTIS, AMARSUPIAL IN DECLINE

The Greater Bilby has shown a rapid decline in range during this centu ry and now occupies only a small isolated area in south-western Queens land (QLD) and a larger but mostly low-density area in the north-weste rn deserts of the Northern Territory (NT) and Western Australia (WA). We have examined variation in the control region of mitochondrial DNA (mtDNA) and. at nine microsatellite loci in order to investigate the e xtent of current and historical subdivision across the species range, and to provide a preliminary assessment of genetic structuring and mat ing system on a finer scale within the QLD population. Both mtDNA and microsatellite loci had substantial variation within and among populat ions, with mtDNA divergence being greater between QLD and NT than betw een NT and WA. The QLD population had two unique and divergent mtDNA l ineages, but there was no evidence for strong phylogeographical struct ure across the range. The available evidence suggests that the bilby s hould be considered as a single Evolutionarily Significant Unit consis ting of multiple Management Units. Augmentation of the remnant QLD pop ulation from the NT does not appear necessary at this stage, at least not on genetic grounds. Finer-scale analysis of microsatellite variati on for two QLD colonies revealed a deficiency of heterozygotes and sig nificantly greater relatedness within than between colonies. However, structuring was observed only for males; relatedness values for female s did not depart from those expected under panmixia. Parentage exclusi on analysis for one colony allowed the construction of a partial pedig ree which indicated strong polygyny, with one male fathering all but o ne of the eight offspring assigned. The extent to which fine-scale gen etic structuring and differences between sexes is due to sex-biased di spersal vs. effects of mating system remain to be determined.