The Impact of Host-Microbe Interactions on Nasonia Evolution
Van Opstal, Edward Jake
The interactions between a host and its associated microbes can convey either beneficial or harmful traits on the host, such as dietary supplementation or reproductive parasitism, respectively. Through host interactions between vertically-transmitted endosymbionts or horizontally-transmitted microbiota, the microbially-conferred traits may be selected for and drive host evolution. In this dissertation, members of the parasitoid wasp genus Nasonia comprised of closely related wasp species were studied for their interaction with a Wolbachia endosymbiont and their gut microbiota. Nasonia must regulate their Wolbachia endosymbiont densities during maternal transmission to prevent long-term, negative fitness effects. Because little is known about evolutionary forces that underpin the regulation of maternally transmitted symbionts, a forward genetic screen was conducted to find a gene responsible for regulating a 80-fold difference in Wolbachia titers between N. vitripennis and N. giraulti. A quantitative trait loci analysis, the introgression of N. vitripennis genomic regions into a N. giraulti background, and RNAi gene knockdown validation identified the maternal effect Wds gene that suppresses Wolbachia titers in N. vitripennis. To study the ecological and evolutionary processes by which Nasonia wasps interact with their gut microbiota, phylosymbiosis was tested and validated as an eco-evolutionary pattern by which the host evolutionary history is paralleled by the similarity in the composition of their gut microbiota. To reveal the importance of phylosymbiosis in Nasonia evolutionary relationships, microbiota transplantation assays were performed with an optimized Nasonia germ-free rearing system. Transplantations of gut microbiota from different Nasonia spp. into a germ-free recipient resulted in reductions in traits related to host fitness, supporting that Nasonia-gut microbiota interactions can drive adaptation and speciation. We conclude that the described interactions between Nasonia and their associated microbes influence Nasonia function and play a role in Nasonia evolutionary processes.