Historical and current patterns of gene flow in the butterfly Pararge aegeria

Aim: We have investigated the phylogeography and genetic structure of the Speckled Wood butterfly (Pararge aegeria) across its entire distribution range and studied its dispersal both on mainland and across sea straits. The apparent lack of gene flow between Sardinia and Corsica was further investigated by means of mating experiments. Location: Europe and North Africa. Methods: We sampled 345 individuals and sequenced one mitochondrial gene (Cytochrome c Oxidase subunit I, COI) for all samples and two nuclear genes (wingless and zerknullt) for a subset of the specimens. A total of 22 females from Corsica and Sardinia were used to establish a series of crosses to investigate reproductive compatibility and were screened for the presence of Wolbachia. Bayesian inference (BI) and haplotype networks were employed to infer phylogenetic relationships and a Principal Coordinate Analysis (PCoA) was used to represent geographical patterns of genetic diversity. Mating and courtship data were analysed using linear mixed effect models. Results: We detected two main COI lineages separated by the Mediterranean Sea and maintained over relatively short sea straits. While nuclear gene variation was generally in agreement with that of COI, this was not the case in all areas (e.g. Iberian Peninsula and Corsica/Sardinia). Mating experiments revealed no evidence of reproductive isolation between the lineages, nor clear relation to Wolbachia infection status. Main conclusions: We propose that following the post‐glacial recolonization of Europe, the ancestral COI lineage of P. aegeria was maintained in North Africa and Mediterranean islands, while a new lineage colonized from Eastern Europe, replacing and apparently out‐competing the ancestral variant. Several hypotheses are discussed that may explain the local discordance between the nuclear genes and COI, including sex‐specific dispersal, selection and differential rates of gene evolution.