The potential role of Wolbachia as an incompatibility factor between cherry infesting Rhagoletis fruit fly species

Wolbachia is a widespread endosymbiotic bacteria that infects a broad range of different arthropod species. A key factor in Wolbachia’s success is its ability to manipulate the reproduction of its host, promoting vertical transmission. A common mechanism Wolbachia uses to influence host reproduction is the induction of cytoplasmic incompatibility (CI). CI can lead to postzygotic reproductive isolation when host populations are infected by different strains of Wolbachia. Rhagoletis fruit flies (Diptera: Tephritidae) are important pests species in North America. The best-studied species in the genus is the apple maggot, Rhagoletis pomonella Walsh. Naturally infesting hawthorns, a population shifted to domesticated apples as a new host that resulted in the formation of an ecologically and genetically distinct host race. This is a famous example of host race formation and first stage of ecological speciation with ongoing gene flow. In contrast to R. pomonella, members of the Rhagoletis cingulata species group radiated by a variety of different modes of speciation. While R. cingulata and R. indifferens were formed by classic allopatric speciation, R. osmanthi and R. chionanthi were formed sympatrically by adaptation to different hosts. Here, we characterize the Wolbachia infection of different R. cingulata populations from the eastern and southwestern United States and R. indifferens from the western United State and compare the infection status with the genetic background of the flies. We describe two different hot spots of ongoing Wolbachia invasion and discuss potential impacts of the endosymbiont on the evolution of the flies.