High effective inbreeding coefficients correlate with morphological abnormalities in populations of South Australian koalas (Phascolarctos cinereus)

Koalas have undergone a series of sequential founding events on islands in south-eastern Australia in recent times, Populations in South Australia at the Eyre Peninsula and Mt Lofty Ranges were founded in the 1960s from a col ony on Kangaroo Island. The Kangaroo Is. colony was derived from animals in troduced to French Island from mainland Victoria over a century ago. In thi s study, we first use microsatellite markers to quantify levels of genetic variation within the South Australian koala populations and the relatively unperturbed Strzelecki Ranges population from mainland Victoria. This analy sis revealed low levels of allelic diversity (1.7 +/- 0.2 to 2.7 +/- 0.5) a nd heterozygosity (0.208 +/- 0.088 to 0.340 +/- 0.110) in the three South A ustralian koala populations relative to the Strzelecki Ranges population, w hich has the highest levels of allelic diversity (4.7 +/- 1.1) and heterozy gosity (0.476 +/- 0.122) in Victoria. Second, we measured the incidence of testicular aplasia, a unilateral or bilateral failure in testicular develop ment, in the Eyre Peninsula and Kangaroo Is. populations, and in the ultima te founding population at French Is. Testicular aplasia was present at a fr equency of 4.3% in French Is., 12.8% in Kangaroo is. and 23.9% in the Eyre Peninsula, but was undetectable in the non-bottle necked Pilliga State Fore st population of New South Wales. The incidence of testicular aplasia corre lated positively with effective inbreeding coefficients derived from hetero zygosity values (0.13 +/- 0.06 in the Pilliga State Forest, 0.57 +/- 0.17 i n French Is., 0.63 +/- 0.12 on Kangaroo Is. and 0.77 +/- 0.12 in the Eyre P eninsula), which may indicate inbreeding depression. These findings are of concern when evaluating the long-term conservation and viability of the Sou th Australian koala populations, which may benefit from genetic augmentatio n in the future. Finally, unconfirmed reports suggested that animals from o ther states in Australia were introduced into the Mt Lofty Ranges populatio n. Therefore, we quantified differentiation between the three South Austral ian populations and the Strzelecki Ranges and French Is. populations, based on microsatellites and mtDNA d-loop region variation. R-statistics and Gol dstein's delta mu square distance revealed that differentiation at nuclear loci between populations paralleled known recent population history, except for the close relationship between Mt Lofty Ranges and French Is. This sug gested a recent contribution to the Mt Lofty Ranges populations of animals derived from the French Is. translocation program. Furthermore, mtDNA d-loo p analysis found no evidence of contributions to the gene pool from animals of New South Wales or Queensland stock, implying that the population was d erived exclusively from Victorian stock.