Abstract # 13365 Event # 29:

Scheduled for Thursday, August 22, 2019 11:15 AM-11:30 AM: (Room 325) Oral Presentation


SOURCES OF VARIATION IN WEANED AGE AMONG WILD CHIMPANZEES IN GOMBE NATIONAL PARK, TANZANIA

E. Lonsdorf1, M. Stanton1, A. Pusey2 and C. Murray3
1Franklin and Marshall College, PO Box 3003, Lancaster, PA 17601, USA, 2Duke University, 3The George Washington University
line
     In primates, lactation and weaning are sensitive to maternal and offspring characteristics and environmental conditions. Little is known about sources of variation in weaning in wild great apes, which are an important comparative reference for human evolution. We used 41 years of observational behavioral data from 65 offspring of 29 mothers to examine the relationships between weaned age in wild chimpanzees and maternal age, rank and parity, and offspring sex. Using a mixed-effects Cox proportional hazards analysis, we found that male offspring were less likely to wean early (HR=0.35, z=-2.08, p=0.037). For individuals with known weaning age (n=37), weaned age of males varied more than weaned age of females (CVmales=24.8, CVfemales=18.0), and mean age of weaning for females was 88.5 days earlier. In addition, maternal dominance rank interacted with offspring age, such that low-ranking mothers were less likely to wean offspring early, but this effect decreased with offspring age (HR=0.9994, z=-2.80, p=0.005). We had limited statistical power to examine parity, but mean weaned age of firstborn offspring (n=7) was 5.1 years, compared to 4.6 years for later born offspring (n=30). Future work to incorporate physiological measures of weaning are planned to develop a more fine-grained understanding of these sources of variation.