April 14 2010

12:00 LSB 2320

Matt Dean
Molecular and Computational Biology, USC

Proteins of male seminal fluid: the evolutionary dynamics of sexual conflict


Beyond viability, the most important task a sexually reproducing organism can accomplish is to pass its gametes to the next generation. Seminal fluid plays an important role in successful fertilization, yet the proteins that are transferred from males to females, and the functions they perform, are not fully characterized. Here, we use isotopic labeling coupled with a mass spectrometry pipeline to identify ejaculated proteins in mice. This is the first comprehensive, direct identification of ejaculated proteins in this model organism. We identified 88 proteins, 75 of which were detected directly from the copulatory plug, a hard coagulum that forms shortly after mating. As a possible form of mate guarding, whereby fertilization by future matings is inhibited, the copulatory plug may be beneficial for males but deleterious for females - that is, it may be a source of evolutionary sexual conflict. Consistent with this hypothesis, copulatory plug proteins evolve at an elevated rate, and are produced at significantly higher abundance, than other ejaculated proteins. Because our approach can separate male- and female-derived proteins, we find that while male-derived proteins are enriched for serine endopeptidase inhibitors, females appear to produce serine endopeptidases in response to mating. One interpretation is that male fitness depends both on the formation and preservation of the copulatory plug, while female fitness depends on her ability to degrade the plug and clear her reproductive tract for future mating. These investigations lay the foundation for understanding the genetic and functional basis of sexual conflict.















































































































































































































































































































































































































































































































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