This is an experimental and theoretical study of the evolution of biochemical characters which are the end results of metabolic pathways. The experimental system focuses on the maintenance of lipid glycogen stores in the fat body of Drosophila melanogaster. Dr. Clark has devised means of quantifying lipid and glycogen storage, along with the activities of other enzymes. Large-scale quantitative genetic studies of these traits has shown extensive genetic variation in both lipid and glycogen storage, and that the variation is in part explainable by the variation in activities of associated enzymes. Two experiments will be performed. The first experiment examines the rate at which spontaneous mutations affecting storage and enzyme kinetic characters accumulate. Mutations that accumulate on a single chromosome can be isolated and retained. Over a 50 generation period (each generation takes about two weeks) series of characters, including lipid and glycogen storage, will be assayed. Rates of mutation for these complex traits, and for the correlated effects of these mutations will be estimated. Only a few studies have estimated mutation rates for quantitative characters, and none of them have an underlying mechanism to be tested. In order to understand how quantitative traits evolve, good estimates of this sort are necessary. The proposed research will provide such estimates. Results of these studies may also find application in the field of pest management, because positive selection acting on a trait like lipid storage is not too unlike selection imposed by application of a pesticide. Response can either be by a specific detoxification, or by complex pathways involving absorption and excretion. As described in one of Dr. Clark's papers, it is also relevant to artificial selection regimes that are imposed on growth and fat contents of a number of agriculturally important animals. The correlated responses to selection can only be understood in light of the allometric relations among traits, which are to a large part genetically determined.
