Hollocher/Davis 9728890 One striking and very common pattern that results when different species are crossed together is the production of hybrid offspring that are unable to reproduce (i.e. the offspring are completely sterile). This research focuses on understanding the genetic and developmental basis of hybrid sterility in offspring that result from crosses between Drosophila melanogaster and Drosophila simulans. Earlier analyses of hybrid sterility had been hampered by the fact that all crosses using these two species yielded offspring that were completely sterile, making simple genetic analyses beyond the initial F1 hybrid impossible. Recently, a naturally occurring strain of D. simulans has been discovered which rescues the sterility defect of hybrid females in crosses with D. melanogaster. With the ability to produce both fertile and sterile hybrid females, we are now in a position to use the vast repertoire of molecular and genetic tools available in these Drosophila species to make advances in understanding the underlying genetic and developmental causes of hybrid sterility. The first aim of this research is to use a comparative developmental approach to characterize the specific defects in gametogenesis that are associated with hybrid sterility. Using this comparative approach we can answer the following questions: What is the developmental basis of female hybrid sterility and its rescue? Do sterile, unrescued hybrid females have any functional germline tissue at all? If so, what appears to be the primary defect in germline development? Is hybrid female sterility rescue complete? Is hybrid sterility rescue sex-specific? Our second aim is to map the genetic factors responsible for hybrid female sterility and its rescue. The generation of recombinants between D. simulans lines that produce either sterile or fertile hybrid females when crossed with D. melanogaster will be used to determine which gene regions are associated with the specific hybrid sterility defects characterized in t he first aim of the proposal. In conjunction with the mapping studies, a survey of additional Drosophila lines will be conducted to isolate new sterility rescue factors, paying particular attention to complementary strains of D. melanogaster which show hybrid sterility rescue. Our final aim is then to take advantage of hybrid sterility rescue in crosses between D. melanogaster and D. simulans to introduce genetic material from one species into the other to test specific hypotheses about how genes affecting gametogenesis have diverged between these two species.
