Sex differences in infant rhesus macaque separation-rejection vocalizations and effects of prenatal androgens

Infant and juvenile rhesus macaques exhibit many sexually dimorphic behavio rs, including rough and tumble play, mounting, and time spent with nonmothe r females. This study investigated sex differences in infant rhesus monkey separation-rejection vocalizations (SRVs), and the effects of altering the prenatal hormone environment on these differences. Pregnant females receive d exogenous androgen (testosterone enanthate), an androgen antagonist (flut amide), or vehicle injections for 30 or 35 days during the second (early) o r third (late) trimester of pregnancy. Control females used a greater perce ntage of coos and arched screams than did control males. In contrast, males used a greater percentage of geckers and noisy screams than did females. F emales also had longer SRV bouts, used more calls, and used more types of v ocalizations than did males. Mothers were more likely to respond to the SRV s of male infants than to the SRVs of female infants. Prenatal flutamide tr eatment early in gestation reduced the likelihood that mothers would respon d to their male offspring, but prenatal androgen treatment had no effect on response rates of mothers to female offspring. Early, but not late, androg en treatment produced females who vocalized in a male-typical manner. Simil arly, early flutamide treatment produced males who displayed more female-ty pical SRVs. Late flutamide treatments of females produced as much masculini zation of SRVs as did early androgen treatment in females. These results de monstrate sex differences in highly emotional vocalizations in infant rhesu s macaques and provide evidence that the timing and form of prenatal hormon al exposure influence such vocalizations. (C) 2001 Academic Press.