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The roots of human hunting and meat eating lie deep in our evolutionary past shared with chimpanzees (Pan troglodytes). From the few habituated wild populations, we know that there is considerable variation in the extent to which chimpanzees consume meat. Expanding our knowledge of meat eating frequencies to more, yet unhabituated, populations requires noninvasive, indirect quantitative techniques. We here evaluate the use of stable isotopes to reconstruct meat-eating behavior in wild chimpanzees. We present hair isotope data (n = 260) of two western chimpanzee (P. troglodytes verus) groups from Taï forest (Côte d'Ivoire) and relate them to directly observed amounts of meat consumed, sex/female reproductive state, and group, while controlling for differences between individuals, seasons, and observation efforts. Succeeding seven months of hunting observations, we collected hair of 25 individuals for sequential analysis of δ 15 N and δ 13 C. Hunting success in the 7-month study period varied between the groups, with 25 successful hunts in the East group and only 8 in the North group. However, our models only found a direct relationship between amounts of meat consumed and variation within individual hair δ 15 N values in the East group, but not in the North group and not when comparing between individuals or groups. Although on average East group individuals consumed more than double the amount of meat than North group individuals, their δ 15 N values were significantly lower, suggesting that differences in microhabitat are substantial between group territories. The effect of sex/female reproductive state was significant in δ 15 N and δ 13 C, suggesting it related to access to food or feeding preferences. We conclude that several factors additional to diet are influencing and thus obscuring the isotope ratios in wild chimpanzee hair, particularly when comparing between sexes and social groups., Competing Interests: Conflict of interest We declare no conflict of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Adaptations associated with shifting from a predominately forested habitat to a more open environment are considered a crucial step in hominin evolution. Understanding how chimpanzees, one of our closest-living relatives, are exposed to the selection pressures associated with living in a relatively sparse, hot, and dry environment can inform us about the relative importance of potential environmental stressors involved in adaptations to drier environments. We investigated the extent to which chimpanzees living in an extreme savanna habitat experience seasonal variability in either energy balance or thermoregulation (dehydration and heat exposure), as well as whether these potential environmental constraints are taxing to chimpanzee individuals. Specifically, we tested the hypothesis that savanna environments impose seasonally-relevant costs to chimpanzees. To this end, we collected 368 urine samples from one community of chimpanzees at Fongoli, Senegal, and measured c-peptide, creatinine, and cortisol as measures of physiological responses to environmental food, water, and heat constraints, respectively. We then evaluated the influence of climatic and phenological factors on these indicators. Results illustrated significant seasonal variation in all biomarkers, which corresponded to relevant ecological correlates. Furthermore, creatinine but not c-peptide correlated with cortisol levels, suggesting that chimpanzees in this environment endure periods of heat and dehydration stress, but are able to avoid stressful levels of negative energy balance. Using savanna chimpanzees as a referential model, our research lends support to the notion that thermoregulatory challenges were a significant factor in hominin evolution, and suggests these challenges may have overshadowed the challenges of maintaining adequate energetic balance during the expansion of the hominin range from wetter to drier environments., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The isotope ecology of great apes is a useful reference for palaeodietary reconstructions in fossil hominins. As extant apes live in C 3 -dominated habitats, variation in isotope signatures is assumed to be low compared to hominoids exploiting C 4 -plant resources. However, isotopic differences between sites and between and within individuals are poorly understood due to the lack of vegetation baseline data. In this comparative study, we included all species of free-ranging African great apes (Pan troglodytes, Pan paniscus, Gorilla sp.). First, we explore differences in isotope baselines across different habitats and whether isotopic signatures in apes can be related to feeding niches (faunivory and folivory). Secondly, we illustrate how stable isotopic variations within African ape populations compare to other extant and extinct primates and discuss possible implications for dietary flexibility. Using 701 carbon and nitrogen isotope data points resulting from 148 sectioned hair samples and an additional collection of 189 fruit samples, we compare six different great ape sites. We investigate the relationship between vegetation baselines and climatic variables, and subsequently correct great ape isotope data to a standardized plant baseline from the respective sites. We obtained temporal isotopic profiles of individual animals by sectioning hair along its growth trajectory. Isotopic signatures of great apes differed between sites, mainly as vegetation isotope baselines were correlated with site-specific climatic conditions. We show that controlling for plant isotopic characteristics at a given site is essential for faunal data interpretation. While accounting for plant baseline effects, we found distinct isotopic profiles for each great ape population. Based on evidence from habituated groups and sympatric great ape species, these differences could possibly be related to faunivory and folivory. Dietary flexibility in apes varied, but temporal variation was overall lower than in fossil hominins and extant baboons, shifting from C 3 to C 4 -resources, providing new perspectives on comparisons between extinct and extant primates., (Copyright © 2016 Elsevier Ltd. All rights reserved.)