The Role of Environment in Drosophila Behavioral Variability and the Genetics of Life History Variation

Abstract

Phenotypic differences among individuals are ubiquitous, but our understanding of their origins and evolutionary consequences is still not complete. Previous work has identified within-genotype behavioral differences that persist even in constant laboratory environments (behavioral variability). Causes of variability have been investigated, though its response to the environment and its adaptive value are largely uncharacterized. In Chapter I, I tested the hypothesis that Drosophila melanogaster behavioral variability could be increased under an enriched environment with more micro-environmental variation. I found that behavioral variability slightly increased under environmental enrichment, but that genotype-by-enrichment effects dominated the behavioral variability response. In Chapter II, I investigated, using a combination of simulations and measurements of wild fly behavior, whether variability in D. melanogaster thermal preference reflects bet-hedging, a risk-spreading evolutionary strategy. I found that the seasonal dynamics of mean preference and genetic determination of variability in wild populations supported a pervasive bet-hedging strategy as predicted by modeling. Differential thermal preference heritability across six sites distributed across the continental U.S. supported modeling results that there are regional differences in the adaptive value of bet-hedging. Unlike behavioral variability, life history trait variation is largely genetic in origin - in Chapter III, I found that the genetic basis of offspring number and weight is highly polygenic, implicating genes previously unknown to have roles in life history. Overall, the results of my studies point to complex relationships among genes and genes and environment in determining phenotypes, as well as an evolutionary role for non-genetic phenotype determination.