The Role of Wolbachia in Rhagoletis Fruit Fly Speciation

Speciation is a fundamental evolutionary process responsible for the great diversity of life on Earth. Main factors contributing to the evolution of reproductive isolation are geographic and ecological isolation. However, oft- forgotten and controversially discussed players in the speciation process of insects are reproduction-manipulating endosymbiotic bacteria of the genus Wolbachia that can form pre- and postzygotic barriers in infected insect populations. The multiply infected Rhagoletis fruit flies are an excellent system to study such effects as the evolutionary history of this genus involves a number radiations with different geographic modes, ranging from classic allopatric divergence to sympatric speciation via host plant shifting. Aim of this proposal is to evaluate the contribution of Wolbachia to speciation in different Rhagoletis species utilizing on-site research at the highly complex structured North American fruit fly populations. The research objective will be accomplished by analyzing Wolbachia strains from different Rhagoletis species groups that have undergone allopatric (e.g., R. suavis group) vs. sympatric (e.g., R. pomonella group) speciation. Following the broadly accepted theory that bacterial reproductive isolation almost always evolves in allopatry, I hypothesize that sympatrically derived species with extant gene flow will share the same strains of Wolbachia while allopatric species will possess different strains. I will test this hypothesis by the characterization of different Rhagoletis populations. Further, Wolbachia strains in parasitoid wasps attacking Rhagoletis flies will be characterized as possible vector of horizontal Wolbachia transmission between Rhagoletis species. This will give new insights into routes of horizontal transmission between different species and the evolution of Wolbachia in geographically separated populations with possible influences into speciation. Going beyond the capabilities of the established MLST system for strain discrimination, a combination of Sanger and next generation high throughput sequencing will be adapted to perform a high resolution characterization of this bacteria. Additionally the Rhagoletis species and their parasitoids will be screened for other bacterial endosymbionts influencing the host`s reproduction. Verifying an active role of Wolbachia in reproductive isolation and Rhagoletis speciation will ultimately require breeding of flies that are depleted of the bacteria to determine the extent that fertility is restored between flies. Thus, a secondary objective of the current proposal is to develop and establish protocols for curing Rhagoletis of Wolbachia, allowing follow-up manipulative studies in the future to confirm a direct connection of Wolbachia with fly reproductive isolation.

No additional funding sources recorded.