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First published online March 14, 2005
Journal of Experimental Biology 208, 1201-1208 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01492
Physiological and morphological correlates of among-individual variation in standard metabolic rate in the leopard frog Rana pipiens
Department of Biology, University of St Thomas, St Paul, MN 55105, USA
* Author for correspondence (e-mail: acsteyermark{at}stthomas.edu)
Accepted 10 January 2005
Rates of standard metabolism (SMR) are highly variable among individuals within vertebrate populations. Because SMR contributes a substantial proportion of an individual's energy budget, among-individual variation in this trait may affect other energetic processes, and potentially fitness. Here, we examine three potential proximate correlates of variation in SMR: organ mass, serum T4 thyroxine and relative mitochondrial content, using flow cytometry. Body-mass-adjusted kidney mass correlated with SMR, but liver, heart, small intestine and gastrocnemius did not. Thyroxine correlated with SMR, as did mitochondrial content. These results suggest several novel proximate physiological and morphological mechanisms that may contribute to among-individual variation in SMR. Variation in SMR may be maintained by diverse environmental conditions. Some conditions, such as low resource availability, may favor individuals with a low SMR, through small organ size, or low thyroxine or mitochondrial content. Other conditions, such as high resource availability, may favor individuals with a high SMR, through large organ size, or high thyroxine or mitochondrial content.
Key words: standard metabolic rate, thyroxine, mitochondria, leopard frog, Rana pipiens
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