Dominance rank and reproductive maturation in male rhesus macaques (Macaca mulatta)

Abstract

The timing of reproductive maturation in females has been linked to differences in dominance status and exposure to males, but less information is available regarding the effect of dominance rank and exposure to females on the pace of reproductive maturation in males. A two-year study of a cohort of nine male rhesus macaques was undertaken to document potential social factors influencing variation in rates of reproductive maturation. The males lived in a large heterosexual group housed in a 0.3 ha outdoor enclosure. Every four weeks the focal subjects were isolated from the group to collect morphometric measurements and blood samples. The results revealed that dominance rank was not significantly correlated with average testosterone concentrations during the mating season. However, the highest ranking adolescent male had higher testosterone concentrations at a younger age, earlier in the mating season, and for a longer duration than did the lowest ranking male. Relative testicular weight was significantly correlated with dominance rank during the premating season, but not the postmating season, among adolescent males. The highest ranking adolescent male also engaged in more affiliative and sexual activity with nonkin, sexually receptive females than did lower ranking conspecifics. These patterns of development provide evidence that high dominance status accelerated reproductive maturation in male rhesus macaques.