WELCH, A.M.; College of Charleston: Heritability of lipid reserves in gray tree frog metamorphs

Condition-dependence has emerged as an important assumption in models of sexual selection and life history evolution. Condition has been defined as a measure of physiological state that reflects the ability of an organism to acquire, store, and/or use resources to enhance its fitness. Under condition-dependence, genetic variance in condition should contribute to the evolvability of traits that are limited by condition. Although condition is difficult or impossible to measure directly, and attempts to do so are often contentious, fat reserves can provide a meaningful proxy. I investigated genetic variation in condition by measuring fat reserves at the end of the metamorphic transition for gray tree frogs (Hyla chrysoscelis). Two measures of fat reserves � whole body lipid content and lipid mass as a percentage of dry mass � showed significant heritability in each of two experimental environments. The heritability of lipid reserves may help explain how variation in performance at metamorphosis is translated into variation in sexual displays and other fitness-related traits in adulthood. Although measuring fat reserves requires destructive sampling, both measures of lipid content were phenotypically correlated with body size and age at metamorphosis, traits that are widely used in amphibian ecology. The genetic correlation between lipid reserves and metamorphic size and age remains to be tested. A significant genetic correlation would validate the use of these non-destructive measures as estimates of condition at metamorphosis. In addition, the strong phenotypic correlation between mass at metamorphosis and percent lipid content reflects increased allocation to energy storage at larger body size. This increased allocation to storage offers a possible mechanism linking metamorphic performance traits to fitness later in the life cycle.