Collaborative Grant: Total Energy Expenditure in Apes Measured Using Doubly Labeled Water

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All organisms must expend energy to accomplish the essential physiological tasks of growth, maintenance, and reproduction. Previous work has shown that species often vary in the amount of energy spent on these tasks, and that this variation has very important effects on species' ecology and pace of life. If we are to fully understand the evolved energetic and life-history strategies of ourselves and other related hominoid primates, it is necessary to acquire comparative data; at present, however, very little is known about the energy expenditure strategies of the living apes. This project will provide this structured comparative data on living apes through investigation of how much energy these species spend each day, and these energy expenditure measurements will be used to test the hypothesis that ape energy expenditures constrain their rates of growth, reproduction, and aging, and reflect their diet and ecology in the wild. Total daily energy expenditure (calories/day) in apes (chimpanzees, bonobos, gorillas, orangutans, and gibbons) will be measured using a technique called the doubly labeled water (DLW) method. DLW tracks the body's rate of carbon dioxide production over a two-week period, which in turn provides an accurate measurement of the calories expended during that time; DLW is considered the gold-standard for measurements of daily energy expenditure. Using ape populations housed in Association of Zoos and Aquariums-accredited zoos, total daily energy expenditure will be measured among adult males and females using the DLW method. In addition to testing hypotheses regarding energy budgets, these measurements will advance the current understanding of the physiology and nutritional requirements of these species, as there are currently very few data available for ape energy expenditure. Broader impacts of this project include a better understanding of the nutritional and metabolic requirements of apes, which may improve management strategies for captive apes and therefore improve the health and well-being of apes in captivity; obesity and other metabolic problems are a leading cause of illness in captive apes. This project also will strengthen and develop the role of U.S. zoos in basic research, and will provide research training and experience for undergraduates at Hunter College, Washington University, University of Cincinnati, and at other institutions near participating zoos. Finally, this project will increase public awareness of scientific research and its benefits, as information regarding the project will be made publicly available at participating zoos.