Sperm proteomics reveals intensified selection on mouse sperm membrane and acrosome genes.

Spermatozoa are a focal point for the impact of sexual selection due to sperm competition and sperm-female interactions in a wide range of sexually reproducing organisms. In-depth molecular investigation of the ramifications of these selective regimes has been limited due to a lack of information concerning the molecular composition of sperm. In this study, we utilize three previously published proteomic data sets in conjunction with our whole mouse sperm proteomic analysis to delineate cellular regions of sperm most impacted by positive selection. Interspecific analysis reveals robust evolutionary acceleration of sperm cell membrane genes (which include genes encoding acrosomal and sperm cell surface proteins) relative to other sperm genes, and evidence for positive selection in approximately 22% of sperm cell membrane components was obtained using maximum likelihood models. The selective forces driving the accelerated evolution of these membrane proteins may occur at a number of locations during sperm development, maturation, and transit through the female reproductive tract where the sperm cell membrane and eventually the acrosome are exposed to the extracellular milieu and available for direct cell-cell interactions.