MIAMEN, A.G.*; FEGHAHATI, H.; LEWNO, A.W.; STEYERMARK, A.C.; University of St. Thomas; University of St. Thomas; University of St. Thomas; University of St. Thomas: What causes among-individual variation in resting metabolic rate?

Organisms are thought to have a limited amount of energy to allocate to processes such as resting metabolism, activity, growth and reproduction. Because the available energy may be fixed in amount, subtle differences in energy allocation to one component of the energy budget may affect energy availability to other components. For example, resting metabolic rate (RMR) does vary between individuals of the same population. This among-individual variation in RMR may then lead to fitness differences. This study examines specific mechanisms of among-individual variation in resting metabolism in leopard frogs, Rana pipiens. We measured resting oxygen consumption of frogs at 23 (C). We then sacrificed the animals, removed the energetically expensive organs (heart, liver, kidney, small intestine, and gastrocnemius), and dried them to constant mass. We also measured plasma T4 thyroxine concentration using ELISA, and mitochondria number in liver using flow cytometry. We examine the correlations between body mass-corrected organ mass, T4, and mitochondrial density, and mass-corrected RMR. Thus, do animals with a low RMR also have proportionately smaller energetically expensive organs, less circulating T4, or fewer mitochondria than do animals with a higher RMR?