Sex differences in juvenile rhesus macaque (Macaca mulatta) agonistic screams: life history differences and effects of prenatal androgens.

This study investigated sex differences in juvenile rhesus macaque (Macaca mulatta) vocal behavior during agonistic contexts, and the effects of prenatal androgens on these differences. A total of 59 subjects (5-8 per treatment group) received exogenous androgen (testosterone enanthate), an anti-androgen (flutamide) or vehicle injections (DMSO) for 30 or 35 days during the second (early) or third (late) trimester of pregnancy. An additional 19 unmanipulated controls were included in the analysis. Screams by juvenile males and females between the ages of 1 and 3 years were compared to the screams of adult female exemplars using a discriminant function analysis. Juvenile females produced more adult-female like screams than did juvenile males. Females exposed to androgen treatment late in gestation produced a more masculine pattern of screams. Flutamide treatment in males either early or late in gestation did not significantly affect scream production. Flutamide treatments in females late in gestation, however, masculinized scream production. Androgen treatments administered late in gestation hyper-masculinized male scream production. No sex differences in the contextual usage of screams emerged. These findings suggest that both life history differences and the early hormone environment contribute to sex differences in juvenile rhesus macaque vocal production. Copyright 2005 Wiley Periodicals, Inc.