Speciation, niche differentiation and reproductive isolation in European cereal leaf beetles (Genus Oulema, Coleoptera, Chrysomelidae)
Zusammenfassung der Projektergebnisse
This project analyzed cereal leaf beetle species in the Oulema melanopus complex, since previous data left open whether different forms are actually diverging host races. In addition, observed subtle differences in the beetles' genitalic morphology could hint to reproductive divergence driven by sexual selection for character displacement. While identification of beetles by morphometric analyses of outer characters mostly agreed with genitalic morphology but diagnosed some intermediate forms, molecular data based on AFLP and mtDNA sequences clearly separated the two species and revealed them as sister species that may have diverged about one million years ago. Experiments on larval performance and beetle behavior were designed to test for ecological differentiation between the two species. Neither larval survival and development, nor adult feeding behavior or female oviposition choice revealed adaptation of the two species to different food plants, on the contrary, preferred plants mostly coincided. The two species may thus be interspecific competitors for the same resources, especially in the little mobile larval stages. They do not follow the common pattern of speciation by host switches observed in many phytophagous insect clades. Although our results are very interesting in taxonomic and agricultural context, the Oulema melanopus complex did not prove to be a good model system to address the processes leading to ecological specialization and, in the long run, speciation.
