1Department of Anthropology, University of New Mexico, 2Department of Human Evolutionary Biology, Harvard University, 3School of Medicine, University of North Carolina
March 26, 2015 10:30, Grand Ballroom D
Offspring growth is influenced by parental investment, but parents are expected to experience tradeoffs in the allocation of resources between successive offspring. The rate of offspring production is predicted to compromise traits of offspring quality, including growth. Over a reproductive lifetime, mothers may also suffer energetic depletion, resulting in a lower ability to invest in later offspring. We examined these predictions as they related to juvenile body size in wild chimpanzees (Pan troglodytes schweinfurthii) in the Kanyawara community, Kibale National Park, Uganda. We assessed body size in juveniles aged 4-15 using residual urinary creatinine excretion, an estimate of lean body mass. Confirming a previous analysis, this index was strongly predicted by juvenile age (females: R2 = 0.86, males: R2 = 0.90, p < 0.001). We used linear models to generate age- and sex-adjusted relative body size estimates for 24 juveniles sampled between 1998 and 2012. Consistent with our prediction, chimpanzees born after a shorter interbirth interval were significantly smaller (r = 0.62, p = 0.02). However, this effect was driven by maternal age, which had an effect opposite to that predicted. Older mothers, who had longer birth intervals, produced larger offspring (r = 0.46, p = 0.02). This was surprising because older mothers had weaker energetic profiles during gestation and lactation. While older females experience constraints on their reproductive rates, their offspring appear to benefit by having less competition with siblings.
Funding: National Science Foundation (award BCS 1355014), American Association of Physical Anthropologists