After 60 years, an answer to the question: what is the Karner blue butterfly?

The Karner blue butterfly (KBB), Lycaeides melissa samuelis, is a federally protected taxon whose relationship to the Melissa blue, Lycaeides melissa, has been a point of contention during the 66 years since the KBB was first described. Using a large population-genomic dataset and a model of population divergence with migration, we investigated the relationship between the KBB and L. melissa, as well as the relationship between L. melissa and a third taxon, Lycaeides idas. We report that gene flow between the KBB and L. melissa is low, and comparable to gene flow between L. melissa and L. idas. Considering this population-genetic evidence, we conclude that the KBB is a unique evolutionary lineage that should be recognized as Lycaeides samuelis.