In many organisms occurring in nature, males and females often demonstrate fitness-related differences in mating. A female may benefit by allowing only certain of the sperm she receives to fertilize her eggs, while a male benefits by encouraging the female to use as many of his sperm as possible, at the expense of other males. When these interests conflict, an evolutionary struggle between males and females results. This struggle can create perpetual change in internal reproductive anatomy and physiology, such that males and females that encounter one another often evolve reproductive systems that are finely tuned to one another, but are different from the reproductive systems of other closely related animals. Such differences in internal reproductive systems may then prevent subsequent interbreeding between groups, contributing to the differences that lead to the origin of new species.
The investigators have discovered evidence of this process within the widely studied genus of fruit flies, Drosophila. When sperm from two closely related species of Drosophila compete for the eggs of a single female, those sperm from a male of the same species as the female invariably out-compete the sperm from the more distantly related male. The proposed research will investigate 1) how widespread evidence of the described process is in the Drosophila genus, 2) how rapidly the described differences in internal reproductive systems can evolve, 3) the mechanism by which sperm gain a competitive advantage over sperm of other species, and 4) the mechanisms of competition among sperm from males of the same species. This project will further our understanding of the importance of internal reproductive phenomena in the origin of differences among species.
