Growth velocity and weaning δ 15 N “Dips” during ontogeny in Macaca mulatta

Objectives: A “dip” in the stable nitrogen isotope ratios (δ 15 N) of subadults in the late weaning/early post‐weaning phase of growth and development has been observed. Speculatively, this is the mechanism of positive nitrogen balance operating among rapidly growing subadults. An alternate hypothesis for δ 15 N dips is that during weaning, subadults eat lower‐ 15 N foods than adults. Methods: This study explores the role of positive nitrogen balance in affecting δ 15 N variation of growing subadults by comparing growth velocity with stable carbon isotope (δ 13 C) and δ 15 N ratios of blood serum from captive rhesus macaques ( Macaca mulatta ) ( n  = 14) with controlled diets during the first 10 months of life. Results: During the first six months, δ 15 N values are inversely correlated with growth in some of the anthropometrics (weight and sagittal circumference). Dips in some infants' δ 15 N values below their mothers' values are observed at the end of the weaning period. However, during this time frame, δ 15 N values of the infants are not correlated with anthropometric indices. Serum stable isotope ratios of lactating and non‐lactating adult females differ significantly. Conclusions: Growth in body mass and size explains some of the variation in infant δ 15 N values, but are not responsible for dips in the late weaning/early post‐weaning phase. It is advised that future research evaluate the extent to which growth in other body systems affects nitrogen balance and δ 15 N dips during ontogeny, and expand on isotopic differences between lactating and non‐lactating females. Am J Phys Anthropol 157:347–357, 2015. © 2015 Wiley Periodicals, Inc.