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

Abstract

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. ß 2005 Wiley Periodicals, Inc. Dev Psychobiol 47: 318-327, 2005.

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“…Among non-human primates, females and juveniles are particularly likely to make use of 'alarm calls" (calls that include high peak frequencies) when confronted with a potential threat (e.g., Brown, Kreiter, Maple, & Sinnott, 1992). The biological basis of such responses is indicated by the extent to which the use of such responses is altered in response to the differential presence of gender-related prenatal hormones (Tomaszycki, Gouzoules, & Wallen, 2001).…”

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“…As juveniles, both males and females use screams in agonistic encounters, but the screams of juvenile males are less like those of adult females than are the screams of juvenile females (Tomaszycki et al, 2005). Adult females, but not males, use a variety of scream types to recruit other members of their social group into agonistic interactions.…”