Unidirectional CI and the consequences of Wolbachia for gene flow and reinforcement

The intracellular bacterial parasites of the genus Wolbachia are widespread among arthropod species. In many hosts, they induce a reproductive incompatibility between uninfected females and infected males. The potential role of this cytoplasmic incompatibility in speciation processes of the bacteria’s hosts has long been debated. In this thesis, we analyze common criticisms of such a role by means of mathematical models, combining Wolbachia infection dynamics and host population genetics. In particular, we are concerned with the following: (i) In order to measure the stability of infection patterns within host metapopulations, we derive critical migration rates. (ii) We evaluate the impact of cytoplasmic incompatibility on gene flow between populations by calculating effective migration rates. (iii) We determine the conditions that favor the evolution of female mating preferences through reinforcement. Finally, (iv) we apply our models to a particular realworld speciation process of two sibling Drosophila species in North America, discuss emerging problems, and suggest future directions of research. In summary, our results implicate that Wolbachia might be a frequent factor in host speciation, but usually only by contributing to overall reproductive isolation among other factors. Reinforcement of premating isolation is selected for only under stringent conditions.