Genomic analysis of Plebejus Kluk (Lycaenidae: Polyommatinae) clarifies taxonomy within Europe

Despite the need to describe Earth's biodiversity, some species groups are notoriously challenging to classify. One example is the genus Plebejus Kluk (Lepidoptera: Lycaenidae: Polyommatinae), which has been the subject of taxonomic debate for decades. Numerous studies have been conducted in North America, but European taxa remain underexplored at the genomic level. To fill this gap, we analysed a ddRAD sequencing dataset comprising all European Plebejus taxa and a selection of Asian and North American ones. Plebejus argus (Linnaeus), Plebejus argyrognomon (Bergsträsser) and Plebejus bellieri (Oberthür) are each recovered as monophyletic with limited gene flow, supporting their species status. Plebejus idas (Linnaeus) is paraphyletic, highlighting the need for a revision of the genus at the Holarctic level. Plebejus corsicus (Bellier) presents clear but limited genetic divergence and should be considered a subspecies of Pl. argus, whereas Plebejus villai (Jutzeler, Leigheb, Manil, Villa & Volpe) is not divergent from Pl. bellieri and should be considered a population of the latter. Pl. argus and Pl. idas present geographic structure following the southern peninsulas, with central and northern European populations clustering with the Balkans, consistent with a scenario of southern glacial refugia and posterior range expansion. We also find widespread Wolbachia Hertig infection across all species except for Pl. argus, with low variation levels in the Wolbachia loci. Lastly, we find evidence of increasing inbreeding levels in mainland Plebejus populations, especially in Eastern Europe, which may be due to land abandonment and agricultural intensification.