STEYERMARK, A.C.*; OATMAN, K.A.; GAVIGLIO, A.M.; WILSON, K.; University of St. Thomas; University of St. Thomas; University of St. Thomas; University of St. Thomas: Among - individual variation in standard metabolic rate: how much, where from, and who cares?

Among individual variation in energetic traits can have several fitness consequences. For example, increased energy allocation to one piece of the energy pie should result in either increased energy acquisition to maintain allocation levels to other pieces of the pie, or decreased allocation to other energetic components, and potentially affecting fitness. Important in understanding how variation affects fitness is determining the sources of this variation: how, mechanistically, is variation in energetic traits manifested? Here, we ask: How much among individual variation exists in standard metabolic rate (SMR) in snapping turtles?; Does the variation have a potential fitness effect?; And what are the mechanistic causes of the variation? We first determined SMR of snapping turtles before and after an eight month hibernation period, and determined change in mass. We then examined several potential correlates of variation in metabolism (body mass, liver mass, cytochrome oxidase, uncoupling protein, and mitochondrial amount) in order to understand the mechanistic basis of variation in energetic traits. Turtles with higher metabolic rates had higher mass loss through the hibernation period than did turtles with low metabolic rates. Neither body mass nor body mass-adjusted liver mass affected metabolic rate, but mitochondrial correlates did. Results from this study suggest considerable variation in metabolic rate; the variation is repeatable; variation affects fitness correlates such as growth; and indicate mechanistic sources of variation in SMR.