Evolution of Cryptocephalus leaf beetles related to C. sericeus (Coleoptera: Chrysomelidae) and the role of hybridization in generating species mtDNA paraphyly

摘要

Autochthonous European insect diversity is the result of the very complex geological, geographic and climatic history of the Mediterranean area. The leaf beetle genus Cryptocephalus has over 250 species in this area. Among them stands out a group nearly endemic from this region consisting of conspicuous metallic green or blue beetles which can be found visiting yellow Asteraceae flowers in most mid- to high-altitude European grasslands: the Linnaean species C. hypochaeridis, C. sericeus, and all their relatives. In all, these are 32 species forming several taxonomically complex groups across Europe. We sampled all morphological diversity in this lineage and characterized it for two mitochondrial DNA genes. The mtDNA phylogeny of this assemblage was inferred, as well as the timing of its diversification using standard mtDNA substitution rates and a hypothetical Messinian vicariant split. The origin of the group can be traced back to western continental Eurasia in the Lower Miocene. Its subsequent taxonomic splits can be linked to specific periods in the formation of Europe, with a marked trend to east-west phylogenetic divides throughout time and space, and a nearly constant rate of diversification. Only during the Pleistocene, a significant increase in diversification rate can be associated with species formation in the C. hypochaeridis and C. sericeus species complexes. Within these latter groups, most taxa show some degree of mtDNA paraphyly as a result of their recent separation and remarkably by episodes of gene flow in areas of secondary contact among recently diverged species, possibly driven by climatic change.