The effect of baculum shape and mating behaviour on mating-induced Prolactin release in female house mice

Male genitalia are subject to rapid divergent evolution, and sexual selection is believed to be responsible for this pattern of evolutionary divergence. Genital stimulation during copulation is an essential feature of sexual reproduction. In mammals, the male intromittent genitalia induces a cascade of physiological and neurological changes in females that promote pregnancy. Previous studies of the house mouse have shown that the shape of the baculum (penis bone) influences male reproductive success and responds to experimentally imposed variation in sexual selection. Here, we test the hypothesis that the baculum is subject to sexual selection due to a stimulatory function during copulation. We selected male and female house mice (Mus musculus domesticus) from families with breeding values at the extremes of baculum shape and performed two series of experimental matings following which we examined the concentration of Prolactin in the blood of females either 15 (“early”) or 75 (“late”) minutes after ejaculation. Our results provide evidence of a mating-induced release of Prolactin in the female house mouse early after ejaculation, the level of which is dependent on an interaction between the shape of the baculum and male sexual behaviour. Our data thereby provide novel insight into the mechanism(s) of sexual selection acting on the mammalian baculum.