Genetic differentiation between populations of the European rose hip fly Rhagoletis alternata

We tested for genetic differentiation between populations of Rhagoletis alternata Fall. (Diptera: Tephritidae) on three different host species. We collected larvae from three rose species of the section Caninae (Rosa canina L., Rosa corymbifera Borkh., and Rosa rubiginosa L.) from 15 sites across Germany, where the three roses occurred together. Additionally, we sampled three sites in Switzerland. Roses differ in morphology (e.g. leaf glands) as well as phenology. We were able to score nine allozyme loci (five polymorphic). Populations from the three hosts did not differ in genetic variability. We found significant genetic differentiation between populations from different host species. However, the differentiation was very low (0.9%). Hence, we found no indication for host races. Furthermore, surprisingly little geographical structure of genetic differentiation was found between populations of this fruit fly across central Europe. We offer three mutually non-exclusive explanations for these findings. First, gene flow between populations of Rh. alternata is high. Second, the pattern of genetic differentiation is based on a recent expansion of the distributional range. Third, the ongoing gene flow between roses of the section Caninae acts as a hybrid bridge. (c) 2007 The Linnean Society of London.