Abstract
C-peptide of insulin presents a promising new tool for behavioral ecologists that allows for regular, non-invasive assessment of energetic condition in wild animals. C-peptide is produced on an equimolar basis with insulin, thus is indicative of the body's response to available glucose and, with repeated measurement, provides a biomarker of energy balance. As yet, few studies have validated the efficacy of C-peptide for monitoring energy balance in wild animals. Here, we assess seasonal and interindividual variation in urinary C-peptide concentrations of East African chimpanzees ( Pan troglodytes schweinfurthii). We assayed 519 urine samples from 13 adult male chimpanzees in the Kanyawara community of Kibale National Park, Uganda. C-peptide levels were significantly predicted by the total amount of fruit and the amount of preferred fruit in the diet. However, chimpanzees had very low C-peptide titers during an epidemic of severe respiratory illness, despite highly favorable feeding conditions. Kanyawara males had significantly lower C-peptide levels than males at Ngogo, a nearby chimpanzee community occupying a more productive habitat. Among Kanyawara males, low-ranking males had consistently higher C-peptide levels than dominant males. While counterintuitive, this result supports previous findings of costs associated with dominance in male chimpanzees. Our preliminary investigations demonstrate that C-peptide has wide applications in field research, providing an accessible tool for evaluating seasonal and individual variation in energetic condition, as well as the costs of processes such as immune function and reproduction.
Highlights
Quantifying the energetic status of animals in the wild is essential for behavioral ecologists studying the effects of environmental variation on energy budgets, social behavior and reproduction
There was a significant positive relationship between the average C-peptide of adult males and the percentage of ripe fruit in the diet. While this finding supports the use of C-peptide as a measure relative energy balance, a large proportion of variance in Cpeptide was unexplained
This study joins other recent research validating the efficacy of Cpeptide for measuring energetic condition in apes (Deschner et al, 2008; Emery Thompson and Knott, 2008; Sherry and Ellison, 2007)
Summary
Quantifying the energetic status of animals in the wild is essential for behavioral ecologists studying the effects of environmental variation on energy budgets, social behavior and reproduction. Accurately and consistently collecting such data in the field is a considerable challenge, for species that cannot be trapped or weighed, or those exhibiting broad dietary diversity and unpredictable food availability. Chimpanzees, like many primate species, present both difficulties. Chimpanzee diets are highly varied, even over short time periods, and individual food species vary widely in their nutritional value (Conklin-Brittain et al, 1998, 2006; Emery Thompson and Wrangham, 2008). Individuals show significant variation in both energetic expenditure and access to particular food resources (Emery Thompson et al, 2007; Murray et al, 2006; Pontzer and Wrangham, 2006), while large group size and flexible social.
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