Dominance rank, cortisol concentrations, and reproductive maturation in male rhesus macaques

Abstract

Among adolescent male rhesus macaques, Macaca mulatta, the highest ranking individual within a cohort has higher testosterone concentrations at a younger age, earlier in the mating season, and for a longer duration than his lower ranking conspecifics. We sought to determine whether such a rank-related pattern of reproductive maturation could be a function of differences in glucocorticoid levels. A 2-yr longitudinal study of a cohort of adolescent males living in a heterosexual group in a one acre outdoor enclosure revealed no differences in cortisol concentrations between high and low status males. Cortisol was not inversely correlated with testosterone in either adolescent or adult males. Young pubescent males had increases in cortisol levels coincident with maturation, while older adolescent males had cortisol concentrations comparable to those of adult males. Low ranking males tended to have more variable cortisol concentrations across time. We conclude that cortisol concentrations are not a function of dominance status and that the timing of reproductive maturation in male rhesus macaques is independent of cortisol concentrations.