Cytological and molecular mechanisms of Wolbachia-mediated parthenogenesis in Trichogramma pretiosum

The transition from sexual to asexual reproduction has occurred repeatedly across multicellular life, despite significant biological constraints. Intracellular microbes, such as the bacterium Wolbachia, can facilitate this transition in haplodiploid arthropods through parthenogenesis induction (PI), which converts unfertilized, haploid eggs into diploid females. In many parasitoid wasps, Wolbachia causes PI through diploidization of the initially haploid embryo, and by promoting female development in the originally male-destined eggs. While the PI phenotype has been linked to diploidization and the sex determination cascade, the Wolbachia factors responsible and the exact mechanisms of interaction have not been determined. In this thesis, I use Wolbachia-infected and uninfected lines of the wasp Trichogramma pretiosum to investigate the mechanistic basis of PI, where I focus on the Wolbachia proteins responsible for the phenotype, and the impacts on host biology. In Chapter 1, I used comparative genomics to identify PI-Wolbachia specific proteins (PifA and PifB), which contained eukaryotic-like domains and indicated the potential for interaction with insect biology. In Chapter 2, I examined the mitotic spindles of early Trichogramma pretiosum embryos, which revealed that Wolbachia-infected embryos often had multipolar spindles and supernumerary microtubule organizing centers when undergoing chromosome segregation failure. In Chapter 3, I investigated how Wolbachia interacts with the sex determination cascade. I found that the Trichogramma pretiosum gene transformer underwent canonical sex-specific splicing, and when infected with Wolbachia, the proportion of traF was significantly higher as compared to uninfected counterparts. Additionally, I found that both host TraF and PifA interacted with Tra2, suggesting PifA may have a role in sex-specific splicing. These findings offer a comprehensive view into both how Wolbachia drives PI and how this manifests in the host, which provides a better understanding of the biological impacts of microbe-mediated asexuality.