Genetic erosion detected in a specialist mammal living in a fast-developing environment

Fragmentation of habitat is a major threat across a wide range of taxa. Subsequent effects include reduced population sizes and isolation of populations. Both can have detrimental consequences for populations as they increase the risk of genetic erosion. While it is critical to prevent and, if required, reverse genetic erosion, we often lack adequate data to assess whether and how much genetic erosion has occurred. Here, we present a genetic monitoring study where we investigated changes in genetic diversity and genetic patterns in a threatened, specialist mammal, the koala (Phascolarctos cinereus). Our study population inhabits an increasingly fragmented landscape and has experienced a sharp decline in population size within the past three decades. We used 1038 single nucleotide polymorphic loci (SNPs) to compare measures of genetic diversity between samples collected in 2018 and in 2006 (two generations prior) and investigated simultaneous changes in the environment. We found a decline in both heterozygosity and effective population size (N-e), and an increase in sub-structuring, average relatedness, and inbreeding (F-IS) alongside an increasingly threatening and more fragmented environment. Given the extent of genetic erosion in only two generations, we urge consideration for the implementation of mitigation measures for this population and for threatened populations in similar conditions. Our study further emphasizes the importance of effective management of at-risk populations including monitoring of genetic erosion.