Using stable isotopes to discern the advantages of tool-mediated shellfish exploitation in a monkey model system

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This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).A preference for high quality protein may have contributed to key changes in our early human ancestors. Researchers have hypothesized that early modern human consumption of marine protein (e.g., shellfish) aided the rapid dispersal of hominins from Africa, and that early stone tools enabled greater access to animal protein and fat that fueled the energetic demands of brain growth and cognition. Testing hypotheses about the importance of marine protein for early human population movements and biological adaptations has been difficult given the dearth of suitable model primate systems. However, this project has identified one such model system, a unique population of macaques that use stones to extract and eat shellfish, with individual monkeys differing in tool-use abilities. The investigators will measure relationships among shellfish consumption, protein levels in individual monkeys, and tool use, to determine how variation in technical competence with stone tools may influence protein intake. The project has broader impacts at the local, national, and international levels, including training and professional development for underrepresented students, international research collaborations with Chulalongkorn University, educational outreach in K-12 settings, and the dissemination of research findings beyond academia through various media. This project will begin to explore the fitness consequences of individual variation in stone tool use and shellfish exploitation. The investigators will use carbon and nitrogen stable isotope analysis to measure the contribution of protein from shellfish consumption to the hair protein of individual monkeys within a stone-tool using population of long-tailed macaques in Koram Island, Thailand, and quantify the benefit of tool use to protein assimilation. These objectives will be achieved by 1) measuring the carbon and nitrogen stable isotope composition of macaque hair and all food sources, and 2) combining isotopic data with behavioral data on foraging (as informative priors) in a Bayesian stable isotope mixing model to estimate the proportional contributions of protein sources to hair as a direct function of stone tool use and technical proficiency.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.