Differentiation in the marbled white butterfly species complex driven by multiple evolutionary forces

Abstract

[Aim] Genetic and phenotypic data may show convergent or contrasting spatial patterns. Discrepancies between markers may develop in response to different evolutionary forces. In this study we analyse inter- and intraspecific differentiation of closely related taxa in the marbled white butterfly species group. Based on genetic and phenotypic characters we test for potential evolutionary drivers and propose a taxonomic revision.

[Location] Western Palaearctic (including north-western Africa).

[Methods] We compared distributions of mitochondrial cytochrome c oxidase subunit I gene (COI) sequences, of several allozyme loci, and of the shape of wings and genitalia obtained by applying landmark-based techniques for the three butterfly species Melanargia galathea (central and eastern Europe), M. lachesis (Iberia) and M. lucasi (North Africa).

[Results] All studied markers showed a strong spatial structure, although discordance among their patterns was detected. COI sequences, wing shape and genitalia indicated a main split between M. galathea and M. lucasi. A lower differentiation between M. galathea and M. lachesis was found in wing shape and reflected in two mutations of the COI gene, while allozymes indicated a strong divergence. Within M. galathea, allozyme data and COI, but not morphology, revealed the existence of a slightly differentiated lineage in the Italian Peninsula, France and Switzerland. Based on COI, Melanargia lucasi was split into two subgroups, a western and an eastern Maghreb lineage.

[Main conclusions] Long-term isolation of Melanargia populations between North Africa and Europe led to divergence between M. galathea and M. lucasi. This was followed by a recent differentiation among populations isolated during the cold periods of the Pleistocene, such as M. lachesis in Iberia. These lineages are characterized by a tendency not to overlap in secondary sympatry. The different patterns of the four markers may arise from divergent evolutionary processes and pressures: wings may be mainly affected by natural selection, genital structures by sexual selection, whereas long-term isolation and drift may have driven divergence of mitochondrial DNA and allozymes.