THE EFFECT OF WOLBACHIA VERSUS GENETIC INCOMPATIBILITIES ON REINFORCEMENT AND SPECIATION

抄録

Wolbachia is a widespread group of intracellular bacteria commonly found in arthropods. In many insect species Wolbachia induce a cytoplasmic mating incompatibility (CI). If different Wolbachia infections occur in the same host species, often bidirectional CI is induced. Bidirectional CI acts as a postzygotic isolation mechanism if parapatric host populations are infected with different Wolbachia strains. Therefore it has been suggested that Wolbachia could promote speciation in their hosts. We investigated theoretically whether Wolbachia-induced bidirectional CI selects for premating isolation and therefore reinforces genetic divergence between parapatric host populations. To achieve this we combined models for Wolbachia dynamics with a well-studied reinforcement model. This new model allows us to compare the effect of bidirectional CI on the evolution of female mating preferences with the situation where postzygotic isolation is caused by recessive nuclear genetic incompatibilities (NI). Our main findings are: (1) bidirectional CI selects for premating isolation with a higher speed and for a wider parameter range than recessive NI; (2) bidirectional CI can stably persist up to migration rates that are two times higher than seen for recessive NI. The latter finding is important because the speed with which mutants at the preference locus spread increases exponentially with the migration rate. In summary, our results show that bidirectional CI selects for rapid premating isolation and so generally support the view that Wolbachia can promote speciation in their hosts.