Genetic variation and structuring in the threatened koala populations of Southeast Queensland

Habitat fragmentation can act to cause reproductive isolation between conspecifics and undermine species’ persistence, though most studies have reported the genetic condition of populations that have already declined to a very small size. We examined genetic diversity within the vulnerable, declining koala (Phascolarctos cinereus) population in Southeast Queensland, Australia to determine the genetic impact of ongoing threatening processes. Five hundred and twelve koalas from ten Southeast Queensland Local Government Areas on the mainland and one island were genotyped at six polymorphic microsatellite loci. Based on Bayesian cluster analysis incorporating spatial data, the regional koala population was subdivided into six clusters, with location of major roads and rivers appearing to be consistent with being barriers to gene flow. The distribution of mtDNA control region haplotypes identified distinct coastal and inland clades suggesting that historically there was gene flow between koalas along the coast (though little interchange between coastal and inland animals). In contrast, koalas from the Koala Coast (Brisbane City, Logan City and Redland Shire) were shown by microsatellite analysis to be genetically distinct from adjacent areas. It is likely, therefore, that more recent reductions in population size and restricted gene flow through urbanisation have contributed to the genetic differentiation of koalas in the Koala Coast region.