The 85th Annual Meeting of the American Association of Physical Anthropologists (2016)

Infant weight growth and weaning age in free-ranging rhesus macaques (Macaca mulatta)


1Department of Anthropology, New York University, 2New York Consortium in Evolutionary Primatology, 3Department of Zoology, University of Cambridge, 4Department of Psychology, New York University, 5Institute for Mind and Biology, The University of Chicago, 6Department of Comparative Human Development, The University of Chicago, 7Junior Research Group of Primate Kin Selection, Department of Primatology, Max Planck institute for Evolutionary Primatology, 8Behavioral Ecology Research Group, Institute of Biology, University of Leipzig

April 16, 2016 , Atrium Ballroom A/B Add to calendar

The threshold weaning weight hypothesis posits that weaning occurs upon achieving a body weight that maximizes the chances of infant survival. In support of the hypothesis, inter-specific comparisons have shown a constant relationship between birth weights and weaning weights irrespective of species’ body size differences and the time taken to reach a ‘threshold’ weaning weight. If weaning is optimized for individual weight and growth over time rather than set at a fixed age, intra-specific variation in weaning age may be due to differences in previous weight growth. We tested this prediction in a free-ranging population of rhesus macaques (Macaca mulatta) on Cayo Santiago, Puerto Rico, by assessing weight-for-age percentile of 216 pre-weaning (< 6 months old) infants. Contrary to our prediction, weight-for-age percentile during the pre-weaning period did not affect weaning age. Based on a characterization of weaning as a substantial decline in suckling, the estimated ratio of weaning weight to birth weight fell within the published haplorhine range of 3.2~4.9. Decline in suckling was significantly delayed for higher-ranking mothers and older-mothers independently. Differences in birth cohort and social group membership were found to explain approximately 12.4% and 26.5%, respectively, of the total variability in infant weight percentile. We consider recent changes in breeding seasonality pattern in this population as a partial explanation for our results. Regardless, using behavioral, demographic and weight data from a large number of infants, the present study extended the idea of threshold weaning weight generated from cross-species data to within-species variation in weaning age.

NSF 0966166 (NYCEP IGERT).