Investigating Pre-mating and Post-mating Reproductive Isolation in Drosophila

Reproductively isolating barriers which inhibit gene flow between species can be broadly classified into pre-mating and post-mating barriers. Pre-mating barriers evolve rapidly and are thought to be important for the initiation of speciation, while post-mating barriers evolve more slowly and are thought to be important for the maintenance of separate species after speciation has occurred. Here I present two studies, each examining one type of reproductive barrier in Drosophila species. Chapter 2 examines hybrids of Drosophila melanogaster with two other species, Drosophila simulans (5 million years diverged) and Drosophila santomea (15 million years diverged), and examines the effects of temperature in post-mating reproductive isolation in these crosses. Post-mating isolation in hybrids with D. melanogaster is temperature sensitive in crosses with D. simulans, but not D. santomea. These data suggest that divergence time and extrinsic factors both play a significant role in post-mating isolation. Chapter 3 examines the cosmopolitan/Zimbabwe mate choice split in D. melanogaster, in which Zimbabwe females only choose to mate with Zimbabwe males. The trait maps strongly to the rim locus on chromosome 3R, and Zimbabwe and cosmopolitan lines differ by two SNPs in rim. Precise gene replacement with CRISPR/Cas9 reveals that the Zimbabwe allele of rim induces a strong Zimbabwe male preference in cosmopolitan flies, suggesting that strong pre-mating isolation can occur as a result of one or two SNP changes.Doctor of Philosoph