Sex differences in the behavior of wild Alouatta caraya infants

Abstract

Several primates show sex-based differences in activity patterns and socialinteractions during infancy. These have been associated with social and reproductive functions of males and females during adulthood and are related to male-male competition. Our goal was to describe behavioral patterns of wild Alouatta caraya male and female infants, a species with sexual dimorphism in body size and behavioral strategies during adulthood. We also examined the relationship between life-history variables, infant sex and age, activity pattern, and social interactions in order to determine if males and females follow different trajectories during early growth. During a 27-month study, we observed 21 male infants and 14 female infants across two similar sites in northern Argentina. Data were analyzed using GLMM tests. We found no differences in suckling time and weaning age between males and females (9.7 mo vs. 9.4 mo) but male infants spent more time feeding and resting than female infants.Also, males invest more time in contact with their mothers than female infants do, and mothers rejected and broke contact with males more frequently than with females. Other behavioral categories did not differ between the sexes. Our results suggest higher nutritional demands of males compared with females that may affect some behaviors. However, mothers of sons did not experience immediate trade-offs between current and future reproduction. Other behaviors expressed similarly between the sexes suggest similar trajectory in development of male and female A. caraya infants, indicating that most differences emerge following the infant period.