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

Abstract

Offspring provisioning is one of the most energetically demanding aspects of reproduction for female mammals. Variation in lactation length and weaning 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) in Taï National Park, Côte d'Ivoire, to quantify weaning in these chimpanzees and explore if infant sex plays a role in maternal investment. We analyzed serial sections of deciduous lateral incisor root dentine from four Taï chimpanzees to establish the δ(15) N signal of nursing infants; we then analyzed serial sections of first permanent mandibular molar root dentine from 12 Taï chimpanzees to provide quantitative δ(15) N data on weaning in this population. Up to 2 years of age both sexes exhibited dentine δ(15) N values ≈2-3‰ higher than adult female Taï chimpanzees, consistent with a nursing signal. Thereafter a steady decrease in δ(15) N values consistent with the onset, and progression, of weaning, was visible. Sex differences were also evident, where male δ(15) N values decreased at a significantly slower rate compared to females. Confirmation of sex differences in maternal investment among Taï chimpanzees, demonstrates the viability of using isotope analysis to investigate weaning in non-human primates. Additionally, assuming that behaviors observed in the Taï 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.

Niche Partitioning in Sympatric Gorilla and Pan from Cameroon: Implications for Life History Strategies and for Reconstructing the Evolution of Hominin Life History

“…Differences in δ 15 N for infant, juvenile and adult gorillas are consistent with a scenario for prolonged nursing and dependency (and/or physiological immaturity), indicated by the elevation of δ 15 N in infants during nursing [102]–[104]. Figure 5 shows a gradual transition from higher to lower δ 15 N from infancy to adulthood, which in gorillas appears to be more abrupt, but also later during somatic development compared to chimpanzees.…”

Growth velocity and weaning δ15N “Dips” during ontogeny in Macaca mulatta

“…15 N values to adult mean values with weaning is expected as breastfeeding frequency and/or intensity declines, in keeping with the "trophic effect" seen with d 15 N (Fahy et al, 2014;Reitsema, 2012). However, isotopic studies of weaning also identify an unexplained "dip" in infant d…”

Reconstruction of breastfeeding and weaning practices using stable isotope and trace element analyses: A review

“…There have been isotopic studies of BWPs in domesticated cattle (Balasse et al, 2001;Balasse and Tresset, 2002;Gillis et al, 2013), dolphins (Niño-Torres et al, 2006;Knoff et al, 2008), wooly mammoths (Metcalfe et al, 2010), otariids (Newsome et al, 2006), killer whales (Newsome et al, 2009), and sea lions (York et al, 2008). Fahy et al (2014) investigated sex differences in the weaning ages of chimpanzees by sequentially analyzing tooth dentin obtained from the Ta€ ı forest, Cote D'ivoire. They showed 1.7 years of age at the start of weaning for both female and male subadults but six months later age at the end of weaning for male than female subadults although the exact age at the end of weaning could not be calculated because of uncertainty over the root growth rate in chimpanzees.…”

“…Furthermore, breastfeeding at night is difficult to observe in wild settings. Geochemical methods have the advantage of the quantitative estimation of nutritional contributions from milk and other foods and provide complementary results to behavioral data for primates (Reitsema, 2011;Fahy et al, 2014). Finally, the reconstruction of BWPs in hominin species preceding Homo sapiens greatly contributes to understand the evolution of human life history, reproductive ecology, and cooperative breeding.…”