Meeting Abstract
P1.67 Tuesday, Jan. 4 Evaluating body condition in metamorphic gray tree frogs (Hyla chrysoscelis) WELCH, A.M.*; THOMAS, J.E.; WITKOWSKI, N.L.; College of Charleston, SC; College of Charleston, SC; College of Charleston, SC welcha@cofc.edu
Organismal fitness may depend on the amount of energy that can be devoted to growth, survival and reproduction. Consequently, stored energy, particularly in the form of fat reserves, is expected to predict future fitness in a variety of organisms. Because fat content is difficult to measure non-destructively, researchers commonly rely on estimates of body condition based on measurements of length and mass. However, the utility of such “condition indices” has been debated. Here, we compare various condition indices using data on linear size, body mass and lipid mass from over 500 newly metamorphosed gray tree frogs, Hyla chrysoscelis. Lipid mass showed an allometric relationship with body size, with proportionately larger fat reserves among larger metamorphs. While body mass was the best predictor of both the absolute mass of lipid reserves and lipid reserves expressed as a percentage of body mass, the recently-proposed “scaled mass index,” which accounts for scaling relationships between mass and length, outperformed the more commonly-used OLS residuals for estimating the relative size of lipid reserves scaled for allometry. Our results demonstrate the utility of the “scaled mass index” for amphibians. In addition, our finding that larger individuals had greater lipid stores reaffirms the use of body size at metamorphosis as a predictor of future fitness among amphibians. The interest in condition indices may, at times, have overshadowed the potential for raw body size to provide important information about an organism’s condition, particularly when all individuals are assessed at a similar stage of development. For example at metamorphosis, both body size and condition may reflect an individual’s success in the larval environment and its potential for fitness in the adult environment.
