The population genetics of the western grey kangaroo, Macropus fuliginosus

The western grey kangaroo, Macropus fuliginosus is one of the largest species of extant macropod and is distributed across most of southern Australia. However, existing research is limited to ecological and captive studies and major gaps in our knowledge remain. In this study, variation at autosomal and Y-chromosome microsatellite loci, as well as the mitochondrial DNA (mtDNA) control region was assessed in M. fuliginosus populations throughout the transcontinental distribution to elucidate aspects of contemporary structure, phylogeography and hybridisation. Overall diversity in M. fuliginosus was among the highest recorded in marsupials at both autosomal microsatellites and mtDNA, although Kangaroo Island was a notable exception. In contrast, Y-chromosome microsatellites showed less diversity, potentially associated with the skewed sex ratio and polygynous mating system. Five genetically distinct units, some associated with landscape discontinuities, were apparent within M. fuliginosus. Of these, the Lake Torrens/Flinders Ranges area represents the most substantial filter, with populations on either side displaying little admixture and reduced male gene flow. Overall high levels of dispersal were evident, with a strong male bias in effective migration rates. The absence of isolation by distance in the east of the range appears associated with the recent eastward expansion or the influence of environmental/ landscape variables on dispersal. Climatic fluctuations during the Pleistocene have influenced the genetic structure of M. fuliginosus, with the temporary historic isolation of north and south-western populations and subsequent eastward expansion into the current distribution, from south-western Australian populations, prior to the last glacial maxima. Colonised during the easterly expansion, the Kangaroo Island population appears to display differing maternal and paternal lineages. M. fuliginosus represents a single evolutionary significant unit comprised of several management units some of which relate to morphological and reproductive variants. Kangaroo Island represents a reproductive and morphological variant resulting from 9,500 years of isolation and drift, rather than a major component of the genetic diversity. Where M. fuliginosus occurs sympatrically with Macropus giganteus two-way introgression was apparent but no Fl hybrids were detected. This level of hybridisation is indicative of occasional breakdowns in reproductive isolation rather than an active contact zone.