Range-wide population genomic structure of the Karner blue butterfly, Plebejus (Lycaeides) samuelis

The Karner blue butterfly, Plebejus (Lycaeides) samuelis, is an endangered North American climate change-vulnerable species that has undergone substantial historical habitat loss and population decline. To better understand the species' genetic status and support Karner blue conservation, we sampled 116 individuals from 22 localities across the species' geographical range in Wisconsin (WI), Michigan (MI), Indiana (IN), and New York (NY). Using genomic analysis, we found that these samples were divided into three major geographic groups, NY, WI, and MI-IN, with populations in WI and MI-IN each further divided into three subgroups. A high level of inbreeding was revealed by inbreeding coefficients above 10% in almost all populations in our study. However, strong correlation between F_ST and geographical distance suggested that genetic divergence between populations increases with distance, such that introducing individuals from more distant populations may be a useful strategy for increasing population-level diversity and preserving the species. We also found that Karner blue populations had lower genetic diversity than closely related species and had more alleles that were present only at low frequencies (