Evolutionary genetics of Wolbachia-induced parthenogenesis in the parasitoid Asobara japonica: Sex determination and sexual decay

Endosymbionts are micro-organisms that live in the cell cytoplasm of their hosts. They are found in over 40% of arthropod species. In some species endosymbionts induce parthenogenetic reproduction (thelytoky) by altering the developmental fate of eggs from males to females. Little is known about the genetic regulation and evolutionary consequences of such infectious parthenogenesis. In this thesis, by reviewing literature I found that similar manipulation phenotypes and mechanisms evolved in parallel in diverged arthropods, suggesting convergent evolution occurs at both levels. I then use the parasitoid Asobara japonica to investigate genetic and evolutionary consequence of infectious parthenogenesis. I show that sex determination in four Asobara wasp species is not the common Complementary Sex Determination type, in which sex is determined by the allelic status of the sex determination gene. Wolbachia density was found to likely determine the gender and ploidy of thelytokous wasps. This led me to propose that diploidization and feminization are two separate steps in early embryonic development during parthenogenesis induction. Genotyping females and their progeny indicated that gamete duplication is the likely mechanism of diploidization. Furthermore, introgression experiments showed that sexual traits decayed in parthenogenetic females and they had a rather simple genetic basis. To facilitate the genetic basis study of the decayed sexual traits, a linkage map was constructed with de novo generated genome-wide single nucleotide polymorphism markers. The results of my research have contributed to our understanding of the genetic regulation and the evolutionary consequences of Wolbachia-induced parthenogenesis, and to the evolution of asexuality overall.