Collaborative Research: Hard Tissue evidence of weaning variation in primates

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Weaning (cessation of breastfeeding) is a critical developmental milestone with important consequences for maternal reproductive strategies and infant outcomes. Modern humans wean their young much earlier on average than the great apes, but the evolutionary origins of this uniquely human pattern are not well understood. This interdisciplinary research project will study behavioral, ecological, physiological, and developmental data for three different wild great ape species, to understand sources of weaning variation in a comparative primate framework. The project will generate a more comprehensive understanding of the biological, ecological and social correlates of weaning variation in our closest living relatives using approaches that are translatable to paleontological contexts, thus contributing to a framework for understanding the evolution of weaning in humans. This project will broaden participation of underrepresented groups in science through structured internships, mentoring and other enhanced training opportunities for students and early career scientists. Research infrastructure will be enhanced by establishing new collaborations and interdisciplinary datasets relevant to many questions at the intersection of primate conservation and human evolutionary biology. Results of this work will advance our understanding of the population dynamics and health of these critically endangered apes, and will be communicated to wildlife veterinarians and park managers to inform conservation strategies, as well as through online and other public venues.The timing of weaning represents a balance of maternal and offspring evolutionary interests, and is sensitive to physiological constraints as well as physical and social environments. However, behavioral observations of living primates cannot distinguish nutritive versus social functions of nursing, and methods for reconstructing weaning in paleontological contexts are limited in their ability to discriminate weaning variation among closely-related taxa. This comparative and multi-proxy study of weaning variation in wild great apes focuses on three ecologically-distinct populations that show pronounced variation in suckling behavior and maternal reproductive strategies: Virunga and Bwindi mountain gorillas, which differ markedly in ecology, and Gombe chimpanzees, which provide an important taxonomic contrast. This project integrates suckling and feeding behavior, physical development, and fecal stable isotope data collected from individuals in life, with chemical characterization of their foods, and morphological and dental trace element analyses of associated skeletons from these populations after death. This research investigates (1) what factors influence variability in weaning-related dietary transitions across living wild chimpanzees and gorillas, (2) how chemical proxies in biological tissues (fecal, dental) relate to behavioral and anatomical proxies of weaning, and (3) how reliably dental trace elements record variability in documented dietary histories at the individual and population levels.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.