Lila Drasner
Pronouns: She/her
Research Mentor(s): Alexandra Rosati
Research Mentor School/College/Department: Psychology / LSA
Program: UROP
Session: Session 5 (2:40pm – 3:30pm)
Authors: Lila Drasner, Margaret Bryer, Alexandra Rosati
Abstract
Many animals show sex differences in social behavior. In wild chimpanzees (Pan troglodytes), females are less social and less aggressive than adult males, differences which have been hypothesized to stem from energetic constraints such as feeding competition and reproductive costs of clinging infants. Semi-free-ranging chimpanzees at Ngamba Island Chimpanzee Sanctuary in Uganda provide a natural experiment to test this proposal as individuals are provisioned and female chimpanzees are on birth control. However, some females have had babies due to failures of birth control, allowing for a test of the impact of infant care in the absence of energetic constraints. We analyzed two years of focal observational data to compare the social behavior of n=4 mothers with n=24 nulliparous females (non-mothers) in the population. We hypothesized that differences in reproductive constraints would lead to behavioral differences between mothers and non-mothers, such that mothers would be less frequently in close proximity with other adult individuals, participate less in grooming, and be less aggressive than females with no offspring. Against our predictions, we found that proximity [chi-sq = 0.72, df = 1, p = 0.39] and grooming rates [chi-sq = 1.65, df = 1, p = 0.20] were not significantly different for mothers versus non-mothers. Indeed, there was a trend for mothers to be more social, indicating that having an infant may actually attract social partners in this context. We will also explore aggression rates. We conclude that when costs related to foraging for food are reduced, reproductive energetic constraints do not prevent mothers from being social. Our findings show that reproductive constraints may be a weaker driver than feeding competition of sex differences in chimpanzee social behavior.
