Lineage-specific targets of positive selection in three leaf beetles with different defence capacity against a parasitic wasp

Parasitoid wasps are the major causes of mortality of many target host species therefore traits related to host immune defence are usually favored by natural selection. One powerful approach to detect functionally important genes under natural selection is through the analysis of directional selection acting upon protein-coding gene sequences across different species. Here, we investigated patterns of positive selection across three close related leaf beetle species with different immune defence capacity against a parasitoid wasp using a Bayesian approach for the McDonald–Kreitman test. Focus upon single-copy orthologs for Coleoptera, as well as candidate immune related genes, we detected positive selection on coding regions in each of the species specific lineages of three species closely related species of Galerucella beetles. Among these, more immune genes were under positive selection in the species with the greatest immunocompetence (G. pusilla) against parasitoid wasps, while almost no immune genes were under positive selection in the species with the least immunocompetence (G. calmariensis).