Stable nitrogen isotope analysis of dentine serial sections elucidate sex differences in weaning patterns of wild chimpanzees (Pan troglodytes).

Offspring provisioning is one of the most energetically demanding aspects of reproduction for female mammals. Variation in lactation length and wean- ing strategies between chimpanzees (Pan troglodytes), our closest living relative, and modern human societies have been reported. When and why these changes occurred is frequently debated. Our study used stable nitrogen isotope data of tooth root dentine from wild Western chimpanzees (Pan troglodytes verus )i n Ta€i National Park, C^ d'Ivoire, to quantify weaning in these chimpanzees and explore if infant sex plays a role in maternal investment. We ana- lyzed serial sections of deciduous lateral incisor root den- tine from four Ta€ chimpanzees to establish the d 15 N signal of nursing infants; we then analyzed serial sections of first permanent mandibular molar root dentine from 12 Ta€i chimpanzees to provide quantitative d 15 Nd ata on weaning in this population. Up to 2 years of age both sexes exhibited dentine d 15 Nv alues2-3& higher than adult female Ta€i chimpanzees, consistent with a nursing signal. Thereafter a steady decrease in d 15 N values con- sistent with the onset, and progression, of weaning, was visible. Sex differences were also evident, where male d 15 N values decreased at a significantly slower rate com- pared to females. Confirmation of sex differences in mater- nal investment among Ta€i chimpanzees, demonstrates the viability of using isotope analysis to investigate weaning in non-human primates. Additionally, assuming that behaviors observed in the Ta€i chimpanzees are illustrative of the ancestral pattern, our results provide a platform to enable the trajectory of weaning in human evolution to be further explored. Am J Phys Anthropol 153:635-642,