WELCH, A. M.; University of North Carolina-Chapel Hill: Ecological genetics of larval and metamorphic traits: how do populations respond to fluctuating selection?

A population�s response to selection depends on the quantitative genetic basis of traits under selection. When populations experience variable environmental conditions, response to selection also depends on the degree to which a given trait is genetically correlated across environments. A genetic correlation across environments would indicate that particular genotypes are always relatively fit, whereas a genotype-by-environment interaction would indicate that a genotype�s relative fitness differs across environments. Amphibians often experience wide year-to-year variation in selective conditions experienced during the larval stage. To evaluate the potential of an amphibian population to respond adaptively to fluctuating selection, I tested the quantitative genetic relationships of four larval traits between two laboratory environments, using gray tree frog (Hyla chrysoscelis) tadpoles. Artificial crosses were used to generate maternal and paternal half-sibships and the tadpoles were raised in the laboratory at two food levels. I measured four traits that are important to fitness in larval anurans: tadpole mass, time to metamorphosis, mass at metamorphosis, and growth. With one exception, the four traits showed significant heritability within each of the two environments. Some traits showed significant genetic correlation between environments, suggesting that even in fluctuating environments an adaptive response to selection is possible. Some traits also showed significant genotype-by-environment interaction, indicating that a response to selection would be somewhat decoupled across environments. Genetic correlations across environments, and the effect of traits on fitness within environments, will together determine the extent of adaptation and the level of genetic variation maintained within a population.