PROMISCUITY is a driving force in primate evolution. It seems a certain protein in semen is evolving faster in species where females have more partners, the first evidence of sexual selection acting at a molecular level.
The more partners a female has, the more intense sperm competition between males becomes. In a bid to win this struggle, male primates in polyandrous societies have evolved better equipment: bigger testes and higher sperm counts, plus more viscous sperm, which may help prevent the sperm of a later partner from reaching the egg.
To document how these changes take place at the molecular level, Bruce Lahn at the University of Chicago, Gerald Wyckoff at the University of Missouri-Kansas City and their colleagues examined the SEMG2 gene, which codes for a protein that makes semen thicken after ejaculation. The researchers compared sequences from 12 different types of primates, ranging from polyandrous chimps to monogamous gibbons.
Advertisement
When they examined the rate of evolution of the gene鈥檚 bases, which are in theory acted on by selection, compared to rates of neutral mutation, upon which selection has no influence, they noticed that species with a high degree of female promiscuity seem to have higher rates of protein evolution (Nature Genetics, DOI: 10.1038/ng1471). That means sexual selection is driving changes in the protein, the researchers suggest.