Dissecting adaptive clinal variation:: markers, inversions and size/stress associations in Drosophila melanogaster from a central field population

Many organisms show latitudinal variation for quantitative traits that is assumed to be due to climatic adaptation. These clines provide an opportunity to study the genetics of the adaptive process both at the phenotypic and the underlying molecular levels. Yet researchers rarely try to link variation in quantitative traits to their underlying molecular genetic basis. We describe a novel approach for exploring the genetic basis for clinal variation in size and stress traits in Drosophila melanogaster. We look for associations between genetic markers and traits that exhibit clinal patterns on the east coast of Australia using a single, geographically central population. There are strong associations between markers found within In( 3R) Payne and variation in size, suggesting that this inversion explains much of the clinal variation in this trait. We also find that development time is associated with the Adh allozyme locus, cold resistance is negatively associated with the In(3L) Payne inversion and a genetic marker for Hsp70, a heat-shock protein, is associated with heat resistance. Finally we discuss the importance of inversions in clinal variation for quantitative traits and for identifying quantitative trait loci.