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

Despite the need to properly describe Earth biodiversity, some species groups are notoriously challenging to classify. One such group is the genus Plebejus (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. The taxa argus, argyrognomon, and bellieri are recovered as monophyletic clades with limited gene flow, supporting their species status. The taxon idas, in its current Holarctic definition, is paraphyletic, suggesting its redefinition as a Palearctic species and highlighting the need for a revision of the genus at the Holarctic level. The taxon corsicus presents clear but limited genetic divergence and should be considered a subspecies of Pl. argus, whereas the taxon villai 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 infection across all species except for Pl. argus, with low variation levels in the Wolbachia loci. Lastly, we also find evidence of increasing inbreeding levels in mainland Plebejus populations, especially in Eastern Europe, which may be due to the expansion of agricultural land abandonment and intensification.