Solitary bees – Potential vectors for gene flow from cultivated to wild strawberries

The genus Fragaria (Rosaceae) contains 24 plant species, including hybrid species such as the octoploid garden strawberry (F. × ananassa). Natural hybridization between Fragaria species has repeatedly been reported, and the potential future cultivation of genetically modified strawberries has made the study of hybridization potential between F. × ananassa and its wild relatives increasingly important. In Europe, F. × ananassa is the only octoploid species present, and the most likely candidate for hybridization is the common diploid woodland strawberry (F. vesca). To date, it is unknown whether pollinator spectra of the two Fragaria species overlap and thus might promote interspecific gene flow. We carried out a survey of flower visitors in northwestern Switzerland to identify major flower visitors of F. vesca and F. × ananassa. This survey indicated that wild bees are the most important shared flower visitors of F. × ananassa and F. vesca. Therefore, we studied flower choice behavior of the common wild bee Osmia bicornis in a greenhouse experiment. Osmia bicornis did not discriminate between F. × ananassa and F. vesca flowers. We conclude that wild bees are important shared flower visitors of both F. × ananassa and F. vesca and are potential vectors for gene flow between cultivated and wild strawberries.