Genomic, Evolutionary and Functional Analyses of Diapause in Drosophila Melanogaster

Understanding the genetic basis of adaptation has been and remains to be one major goal of ecological and evolutionary genetics. The variation in diapause propensity in the model organism Drosophila melanogaster represents different life-history strategies underlying adaptation to regular and widespread environmental heterogeneity, thus provides an ideal model to study the genetic control of ecologically important complex phenotype. This work employs global genomic and transcriptomic approaches to identify genetic polymorphisms co-segregating with diapause propensity, as well as genes that are differentially regulated at the transcriptional level as a function of the diapause phenotype. I show that genetic polymorphisms co-segregating with diapause propensity are found throughout all major chromosomes, demonstrating that diapause is a multi-genic trait. I show that diapause in D. melanogaster is an actively regulated phenotype at the transcriptional level, suggesting that diapause is not a simple physiological or reproductive quiescence. I also demonstrate that genetic polymorphisms co-segregating with diapause propensity, as well as genes differentially expressed as a function of diapause are enriched for clinally varying and seasonal oscillating SNPs, supporting the hypothesis that natural variation in diapause propensity underlies adaptation to spatially and temporally varying selective pressures. In addition to global genomic and transcriptomic screens, I also performed functional analysis of one candidate polymorphism on the gene Crystalllin, which represents an intersection of multiple global screens related to seasonal adaptation. I show that this polymorphism affects patterns of gene expression and a subset of fitness-related phenotypes including diapause, in an environment-specific manner. Taken together, this work provide a holistic view of the genetic basis of a complex trait underlying climatic adaptation in wild populations of D. melanogaster, linking genetic polymorphism, gene regulation, organismal phenotype, population dynamics and environmental parameters.