Abstract
Organisms are exceptionally well fit to their environments. It has been recognized that this fit is created by the actions of natural selection on phenotypic (and genetic) variation in populations. This adaptation generally happens in a species-wide manner, but heterogeneous environmental conditions across a species range can also lead to local adaptation. Heterogeneous selective pressures may be biotic, such as the frequency or identity of pathogens in the environment, or abiotic, such as ambient temperature. Resistance to infection is an important fitness trait and is certain to be subject to selection. Pathogens therefore represent an important selective pressure, and heterogeneity in pathogen prevalence might be expected to lead to adaptation to local pathogens. Local adaptation leads to genetic differentiation between populations and is quantifiable by comparison of DNA sequences. For my thesis, I will address this question by combining a variety of sampling techniques. First, I will quantify the geographic and temporal heterogeneity in bacteria causing infection in Drosophila melanogaster. Second, I will determine the genetic substructure in immune response genes in D. melanogaster.
