SREL Reprint #1938





Estimation of the Metabolic Rate of the Desert Iguana (Dipsosaurus dorsalis) by a Radionuclide Technique

Eric L. Peters1
Shawki A. Ibrahim
C. Richard Tracy
F. Ward Whicker
Kenneth A. Nagy

1Department of Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523
2Department of Biology, Colorado State University, Fort Collins, Colorado 80523
3Laboratory of Biomedical and Environmental Sciences, University of California, Los Angeles, Los Angeles, California 90024

We describe a method for measuring metabolic rates (MRs) of ectotherms using successive measurements of radionuclide body burdens, which may provide an alternative means of measuring field metabolic rate (FMR). Although MRs can be measured in the laboratory, variability in food supply and quality, temperature, activity, and other factors preclude the direct application of such data to field conditions, Recently, the doubly labeled water (DIW) technique has been successfully applied to estimate FMR in a variety of animals, but this method is expensive, requires special equipment, necessitates the sampling of blood or other body fluids, and may be unsuitable for certain species. We compared the rates of elimination of seven radionuclides with estimates of MRs (CO2 production) from DLW measurements in the desert iguana, Dipsosaurus dorsalis. We observed temperature-dependent elimination for five of the radioniuclides, and found a high correlation (r2 = 0.9.3) between the slopes of individual 86Rb elimination curves and the MRs estimated by the DLW technique. This correlation appeared to be relatively insensitive to differences in water turnover and ingestion of the stable nutrient analog (K). The results suggest that a practical and inexpensive method for measuring FMRs of ectotberms may be derived from this relationship.

SREL Reprint #1938

Peters, E.L., S.A. Ibrahim, C.R. Tracy, F.W. Whicker, and K.A. Nagy. 1995. Estimation of the metabolic rate of the desert iguana (Dipsosaurus dorsalis) by a radionuclide technique. Physiological Zoology 68:316-341.

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