SREL Reprint #1938
Estimation of the Metabolic Rate of the Desert Iguana (Dipsosaurus dorsalis) by a Radionuclide Technique
Eric L. Peters1
Shawki A. Ibrahim1
C. Richard Tracy2
F. Ward Whicker1
Kenneth A. Nagy3
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
Abstract
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.
