Sexual selection halts the relaxation of protamine 2 among rodents.
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.
Reproductive Ecology and Biology Group, Museo Nacional de Ciencias Naturales (CSIC), Madrid, Spain.
Lena
L
Lüke
Alberto
A
Vicens
Francois
F
Serra
Juan Jose
JJ
Luque-Larena
Hernán
H
Dopazo
Eduardo R S
ER
Roldan
Montserrat
M
Gomendio
D000595:Amino Acid Sequence; D000818:Animals; D005075:Biological Evolution; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011479:Protamines / Q000737:chemistry / Q000378:metabolism*; D012377:Rodentia; D017386:Sequence Homology, Amino Acid; D012726:Sexual Behavior, Animal
D011479:Protamines; C068621:protamine 2