TY - JOUR T1 - Sexual selection halts the relaxation of protamine 2 among rodents. JF - PloS one Y1 - 2011 A1 - Lüke, Lena A1 - Vicens, Alberto A1 - Serra, François A1 - Luque-Larena, Juan Jose A1 - Dopazo, Hernán A1 - Roldan, Eduardo R S A1 - Gomendio, Montserrat AB - Sexual selection has been proposed as the driving force promoting the rapid evolutionary changes observed in some reproductive genes including protamines. We test this hypothesis in a group of rodents which show marked differences in the intensity of sexual selection. Levels of sperm competition were not associated with the evolutionary rates of protamine 1 but, contrary to expectations, were negatively related to the evolutionary rate of cleaved- and mature-protamine 2. Since both domains were found to be under relaxation, our findings reveal an unforeseen role of sexual selection: to halt the degree of degeneration that proteins within families may experience due to functional redundancy. The degree of relaxation of protamine 2 in this group of rodents is such that in some species it has become dysfunctional and it is not expressed in mature spermatozoa. In contrast, protamine 1 is functionally conserved but shows directed positive selection on specific sites which are functionally relevant such as DNA-anchoring domains and phosphorylation sites. We conclude that in rodents protamine 2 is under relaxation and that sexual selection removes deleterious mutations among species with high levels of sperm competition to maintain the protein functional and the spermatozoa competitive. VL - 6 UR - http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0029247 ER -