Contrasting segregation patterns among endogenous retroviruses across the koala population.

Koalas (Phascolarctos cinereus) have experienced a history of retroviral epidemics leaving their trace as heritable endogenous retroviruses (ERVs) in their genomes. A recently identified ERV lineage, named phaCin-β, shows a pattern of recent, possibly current, activity with high insertional polymorphism in the population. Here, we investigate geographic patterns of three focal ERV lineages of increasing estimated ages, from the koala retrovirus (KoRV) to phaCin-β and to phaCin-β-like, using the whole-genome sequencing of 430 koalas from the Koala Genome Survey. Thousands of ERV loci were found across the population, with contrasting patterns of polymorphism. Northern individuals had thousands of KoRV integrations and hundreds of phaCin-β ERVs. In contrast, southern individuals had higher phaCin-β frequencies, possibly reflecting more recent activity and a founder effect. Overall, our findings suggest high ERV burden in koalas, reflecting historic retrovirus-host interactions. Importantly, the ERV catalogue supplies improved markers for conservation genetics in this endangered species.