Population genetics of accessory gland proteins and male-female post-mating interactions in Drosophila melanogaster

It has been argued that male-female post-mating interactions drive rapid divergence of reproductive proteins between populations, leading to reproductive isolation and speciation. Here I report on three studies of Drosophila melanogaster populations that aim to shed light on the role of post-mating interactions in reproductive protein evolution, population divergence, the evolutionary processes that influence postmating interactions, and the potential genetic mechanism involved in the evolutionary processes. First I tested the hypothesis of rapid inter-population divergence of reproductive proteins by comparing a pair of populations reported to be undergoing sympatric speciation in Evolution Canyon, Israel. Contrary to expectations, I found no evidence of genetic differentiation between the two populations. I also conducted mate choice tests to determine if populations mate assortatively, as had been suggested by previous work. There was no significant departure from random mating in mixtures of flies from the two populations. I concluded that these two populations are not experiencing incipient sympatric speciation. Secondly, I tested for the influence of four evolutionary effects (sexual conflict, sexual selection by cryptic female choice, temperature-dependent selection, and inbreeding avoidance) on post-mating interactions using a pair of allopatric populations and a pair of temperature-selected lines. I demonstrate that relatedness of mates is a key determinant of male-female post-mating interactions by suppressing offspring productivity of singly mated females. This supports the post-mating inbreeding avoidance hypothesis. Lastly, I investigated two candidate reproductive protein loci (Acps) for their role in post-mating inbreeding avoidance and recognition of relatedness. Females from a U.S. population were crossed to males from an Israel population and matched for the same or different Acp genotype. After controlling for the effect of intrinsic male differences on offspring productivity, I found a significant association between lowered female fecundity and the similarity of the female and male at one of the Acp loci, Acp29AB. This is a novel finding that locus Acp29AB is involved in mediating the recognition of relatedness necessary for post-mating inbreeding avoidance in D. melanogaster.