Growth velocity and weaning δ15N Dips during ontogeny in Macaca mulatta

Objectives:A dip in the stable nitrogen isotope ratios (N-15) 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 N-15 dips is that during weaning, subadults eat lower-N-15 foods than adults. Methods:This study explores the role of positive nitrogen balance in affecting N-15 variation of growing subadults by comparing growth velocity with stable carbon isotope (C-13) and N-15 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, N-15 values are inversely correlated with growth in some of the anthropometrics (weight and sagittal circumference). Dips in some infants' N-15 values below their mothers' values are observed at the end of the weaning period. However, during this time frame, N-15 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 N-15 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 N-15 dips during ontogeny, and expand on isotopic differences between lactating and non-lactating females. Am J Phys Anthropol 157:347-357, 2015. (c) 2015 Wiley Periodicals, Inc.