Phytophagous insects represent not only one of the major radiations on earth but also comprise some of the strongest cases for sympatric speciation to date. Two crucial steps in the formation of new species, niche differentiation and reproductive isolation between emerging species, can especially easily be delimited and tested here. This proposal aims to trace both steps using cereal leaf beetles (Oulema spp.) as a model system. The genus Oulema comprises several grass (Graminaceae) feeding species in Europ e. Based on variation in external and genitalic morphology, it has been claimed that the cereal pest species, O. melanopus, includes a second cryptic species, O. rufocyanea. Through a combination of breeding, rearing and food choice experiments, we plan to establish whether these two sympatric forms actually constitute separate species or rather incipient species that are currently diverging in their feeding habits and reproductive characters. Morphological scoring of presumed diagnostic characters and gene tic analysis of gene flow between the two forms by AFLP (amplified fragment length polymorphisms) will complement the data. To trace the order of speciation events that were or were not associated with host shifts in the European Oulema species, a phylogenetic analysis based on mtDNA sequences will be undertaken.
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