Molecular phylogeny of reed beetles (Col., Chrysomelidae, Donaciinae): the signature of ecological specialization and geographical isolation.

The Donaciinae consist of approximately 165 species predominantly occurring in the northern hemisphere. We analysed mitochondrial and nuclear DNA (COI, EF-1alpha) of 46 species to investigate their phylogeny and to discuss general topics in the context of insect herbivory (generalists versus specialists, ecological speciation). Phylogenetic reconstructions from various methodical approaches yielded very similar results. Clades corresponding to the traditional tribes/genera were recovered. Within the genus Donacia, species groups with characteristic host plant preference were identified. Estimated divergence times are discussed on the background of geological events. The origin of the Donaciinae is dated to 75-100 million years before present, after which they quickly diversified into the main groups. An initial split of those groups occurred in the Palaeocene. In the Eocene and Oligocene, major lineages specialized on certain host plants, where they radiated in the Miocene. This radiation was enforced by geographic isolation brought about by the final separation of America and Europe, after which there arose continental lineages within three larger species groups. In their evolution based on ecological specialization with a recently superimposed geographic isolation, the Donaciinae follow a pattern of specialists arising from generalists. Host plant shifts show that such a specialization is not necessarily an 'evolutionary dead-end'.