Contrasting genetic differentiation of urban and rural populations of two grassland lepidopterans across Europe

Urbanisation is transforming environments globally. The altered abiotic conditions and biotic interactions in urban habitats inflict divergent selection pressures on urban versus rural populations. Genetic drift may simultaneously be significant in typically small urban populations. A key question in urban evolution is whether urban genotypes have a single or multiple origins, but such assessments remain rare, precluding generalizations. We expect similar patterns in species that share ecological traits, but such replicates are missing. To address whether urban and rural populations are genetically differentiated and what is the origin of urban genotypes, we conducted an extensive population genomic ddRADseq analysis of two non-model grassland lepidopterans, Coenonympha pamphilus and Chiasmia clathrata , across Europe. Although the species share ecological traits, their genetic population structures were strikingly different: C. pamphilus had strong population differentiation, while this was almost absent in C. clathrata , which instead showed signs of recent strong population expansion. Although this signature of population expansion complicates inferences, it is nonetheless plausible that the urban populations of both species have multiple origins. This study highlights that urban evolution research needs to integrate phylogeography, because population history affects urban evolutionary dynamics.