The effects of female-male friendships on male postcopulatory levels of oxytocin and vasopressin, and sperm parameters in Macacaarctoides.

Male and female stump-tailed macaques (Macaca arctoides) form close relationships akin to human friendships. Oxytocin and vasopressin modulate these and other social relationships and reproductive behavior and physiology in various mammal species. Besides the behavioral effects of oxytocin, this hormone plays an essential role in the ejaculatory process, favoring sperm transport upward the female reproductive tract.