01980nas a2200217   4500008004100000022001400041245007200055210006900127260000900196300001100205490000600216520130500222100001601527700002001543700002101563700002901584700002001613700002501633700002501658856007901683       2011                        eng d  a1932-620300aSexual selection halts the relaxation of protamine 2 among rodents.0 aSexual selection halts the relaxation of protamine 2 among roden  c2011  ae292470 v63 aSexual 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.1 aLüke, Lena1 aVicens, Alberto1 aSerra, François1 aLuque-Larena, Juan, Jose1 aDopazo, Hernán1 aRoldan, Eduardo, R S1 aGomendio, Montserrat  uhttp://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0029247