title: 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.
authors.affiliation: Max Planck Institute for Evolutionary Anthropology, Department of Human Evolution, Deutscher Platz 6, 04103, Leipzig, Germany; Max Planck Institute for Evolutionary Anthropology, Department of Primatology, Deutscher Platz 6, 04103, Leipzig, Germany.
authors.forename: Geraldine E
authors.initials: GE
authors.lastname: Fahy
authors.forename: Michael P
authors.initials: MP
authors.lastname: Richards
authors.forename: Benjamin T
authors.initials: BT
authors.lastname: Fuller
authors.forename: Tobias
authors.initials: T
authors.lastname: Deschner
authors.forename: Jean-Jacques
authors.initials: JJ
authors.lastname: Hublin
authors.forename: Christophe
authors.initials: C
authors.lastname: Boesch
mesh_terms: D000818:Animals; D000885:Anthropology, Physical; D005075:Biological Evolution; D003804:Dentin / Q000737:chemistry*; D005260:Female; D008297:Male; D009587:Nitrogen Isotopes / Q000032:analysis; D002679:Pan troglodytes / Q000502:physiology*; D012727:Sex Characteristics; D014886:Weaning
chemical_list: D009587:Nitrogen Isotopes
keywords: human evolution; lactation; maternal investment; primatology