Male Reproductive Endocrinology

Androgens, including testosterone, form an integral part of the reproductive endocrinology of male primates. They regulate the development and functioning of male sex organs and they stimulate the growth and maintenance of male secondary sexual characteristics. Androgens also play an important role in modulating sexual, aggressive, and parental behavior. The challenge hypothesis posits that an increase in androgen concentrations is closely associated with levels of male intrasexual competition in a reproductive context. This has received widespread support among primates. In many primate species, androgen concentrations are highest during the mating season, in high-ranking males, during mate-guarding efforts, or during encounters with extragroup male opponents. However, not all variation in androgen modulation observed in primates can be explained by the challenge hypothesis, and additional variables such as nonaggressive forms of male competition and male-female relationships may influence the hormone-behavior interaction underlying male reproductive strategies in some primate species.