Heterogeneous patterns of heterozygosity loss in isolated populations of the threatened eastern barred bandicoot (Perameles gunnii)

Perameles gunnii is an endangered terrestrial marsupial on mainland Australia, but comparitively widespread in Tasmania. No research has yet aimed to assess population structure or genetic diversity in this state until now, where we assess genomic similarity and diversity using a ddRAD dataset of 117 Tasmanian animals.

First, we assigned all samples to populations (or demes), according to their coordinate metadata and known geographic boundaries. We then test this hypothesis with population-ignorant genetic clustering analyses: PCA, Structure, and fineRADstructure. Validating seven (7) populations, four in a distinct "northern" group and three in a "southern" groupd, and also identify two populations displaying significant and unexpected isolation. We then looked to directly assess migration between these populations find little evidence, although genetic similarity within nothern and southern groups suggests that gradual mixing is ongoing within these areas.

We assessed autosomal heterozygosity of individuals using a custom bioinformatic pipeline, and use a Kriging approach to plot regions of Tasmania where higher and lower heterozygosity individuals occur, finding unequal distribution of heterozygosity across geographic barriers that did not appear to affect genetic similarit-based analyses, potentially indicating emerging substructure within populations. We found individual heterozygosities varied within demes by up to a factor of two, and demes with low heterozygosity individuals also still contained those with high heterozygosity. 

Our results provide novel insights into the relationship between isolation-driven genetic structure and local heterozygosity patterns. These may help improve translocation efforts, by identifying populations in need of assistance, and by providing an individualized metric for identifying source animals for translocation.