Evidence for Correlated Evolution of Sexual Selection and Pseudogenization in Primate Fertilization

Abstract

AbstractThe mouse sperm protein ZP3R interacts with proteins in the egg coat and mediates sperm–egg adhesion in a species-specific manner. Understanding the function and evolution of such genes has important implications for studies of reproductive success, infertility, and speciation. A recent analysis showed that (1) the human pseudogene C4BPAP1 is the ortholog of Zp3r, (2) ZP3R pseudogenization evolved independently in eight additional primate lineages, and (3) functional ZP3R genes evolve under positive selection among 20 other primate species for which the gene structure is known. The causes of this pseudogenization of ZP3R are unknown. To explore one plausible cause (relaxation of sexual selection on males), we compared sexual size dimorphism and mating system among primate lineages with and without a functional ZP3R. We found that traits associated with more intense sexual selection on males (greater sexual size dimorphism, polygyny) are associated with functional ZP3R expression, and suggest that a relaxation of sexual selection may be associated with ZP3R pseudogenization. This proposed causal relationship implies an evolutionary cost to maintaining redundancy in the suite of primate fertilization genes.