Evolutionary genetics of male quality and competitive reproductive success

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Name a species in nature, and chances are, its females use sperm from more than one male, resulting in multiple paternity of offspring. This sperm competition generates strong selection that drives rapid evolution of both male and female reproductive traits and may contribute to the maintenance of species boundaries. Despite its evolutionary importance, sperm competition has been difficult to study within its natural environment, the female reproductive tract, because sperm from different males are generally indistinguishable, and the female reproductive tract is often poorly suited for microscopy. The proposed research exploits the experimental and genetic tractability of the fruit fly, Drosophila melanogaster, to generate 200 genetically differentiated populations whose sperm heads express a green or red fluorescent marker. Thus, the research will investigate how sperm variation contributes to sperm competitive success, how sperm traits genetically vary and covary, and ask how the female's genome contributes to her sons' sperm traits. The research will also quantify male×male×female genetic interactions and examine how rearing environment impacts sperm traits.The proposed research will greatly advance understanding of the complex genetics of sperm traits and of sperm-female interactions underlying variation in reproductive success. Human infertility diagnoses of unknown cause may be a consequence of interactions between partners, but distinguishing potential sources of incompatibility necessitates a detailed understanding of reproductive processes and the genetics of reproductive success. Also, fluorescent-sperm populations generated for this research are proving valuable in laboratories worldwide studying genetics, development and fertilization and in educating the public about reproductive biology.