Potential applications of urinary C‐peptide of insulin for comparative energetics research

Abstract

The study of comparative energetics offers a valuable way to identify broad ecological principles and assess the functional significance of energetic adaptations during the course of evolution. Yet, the quantification of energetic status for nonhuman primates under natural conditions remains one of the most challenging aspects of comparative energetics research. Here, we report on the development of a noninvasive field method for measuring energetic status in great apes, humans, and possibly other nonhuman primates. Specifically, we have explored measurement of a urinary metabolite of insulin (C-peptide) as a physiological marker of energetic condition in chimpanzees and orangutans. We performed three validation studies and successfully measured C-peptide in urine samples from captive chimpanzees, wild chimpanzees, and wild orangutans. Urinary C-peptide measures gave indications of being a reliable signal of energetic status in both species. For chimpanzees and orangutans in the wild, baseline urinary C-peptide levels were higher during periods of fruit abundance than periods of low fruit availability. Urinary C-peptide levels were also higher for well-fed captive chimpanzees compared with wild chimpanzees. Although sample size was small, top-ranking male chimpanzees showed higher C-peptide levels in the wild than low-ranking males only during the period of fruit abundance. These preliminary results indicate that further development of the urinary C-peptide method could expand opportunities to quantify energetic condition for great apes in the wild and generate new data for comparative research. We highlight specific applications for studying great ape reproduction as well as the nutritional ecology of human foragers.

Urinary C-peptide tracks seasonal and individual variation in energy balance in wild chimpanzees

“…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). These data provide the first thorough test of the method for chimpanzees, applying a large sample to illustrate that basic measures of dietary quality account for a substantial portion of the variation in male C-peptide concentrations.…”

“…Here we show that known habitat differences between two chimpanzee home ranges in Kibale National Park are reflected in the C-peptide levels of community members. Sherry and Ellison (2007) similarly demonstrated that captive chimpanzees had higher C-peptide levels than their energeticallystressed, wild counterparts. In addition to providing a metric for energetic variation between communities, these findings demonstrate that C-peptide levels in apes reflect individual variation in energetic condition.…”

“…C-peptide of insulin was assayed with a commercial radioimmunoassay kit (DSL-7000, Diagnostic Systems Laboratories, Webster, TX; see also Ellison and Valeggia, 2003;Emery Thompson and Knott, 2008;Sherry and Ellison, 2007), following the manufacturer's overnight protocol with the exception that samples were assayed at full concentration (1:1) to maximize recoveries within the range of the standard curve. Interassay (N = 13) and intraassay coefficients of variation were 8% and 12%, respectively.…”

“…Furthermore, C-peptide can be measured in urine, and urinary concentrations correlate with those in serum (Gjessing et al, 1989;Kruszynska et al, 1987;Meistas et al, 1982). This has recently been demonstrated for chimpanzees specifically (Sherry and Ellison, 2007). In addition to being noninvasive, urine sampling for hormones has the advantage that it provides a measurement over a longer period of hormonal release than in blood, evening out transient fluctuations (Whitten et al, 1998).…”

“…Emery Thompson and Knott (2008) found strong significant correlations of C-peptide with both ripe fruit availability and caloric intake estimates for orangutans in the wild. For chimpanzees, Sherry and Ellison (2007) reported that well-fed captive subjects had significantly elevated C-peptide titers compared with wild subjects. Using a preliminary sample of 25 urine specimens from male chimpanzees in our community at Kanyawara, Kibale National Park, Uganda, they also suggested that C-peptide levels could distinguish fruit-poor from fruit-rich periods, and that dominant males were in better energetic condition than subordinates.…”