| Adaptation to new habitats requires the acquisition of new life history characteristics that may be linked to the main glycolytic pathways. Understanding the evolutionary dynamics that shape genetic variation and lead to phenotypic adaptation requires multiple levels of analysis of relevant points along a pathway. In order to understand the process of translation of genotypic variation into phenotypic variation, a population genetic and functional genomic approach is adopted and concentrated on the glycolytic enzymes of trehalose and glycogen pathway.;First, the molecular evolution of Glucose-6-phosphatase (G6pase ), Udp-glucose pyrophosphorylase (Ugp), Trehalose (Treh) and Trehalose-6-phosphate synthase (Tps1) are analyzed in D. melanogaster and in its sibling species D. simulans. A pattern consistent with adaptive protein evolution is observed at the Treh locus in D. melanogaster . Along the D. simulans lineage adaptive amino acid fixation is observed at the G6pase and Tps1 loci, where as the Treh showed relaxation of selection.;An analysis of geographical variation is conducted along the east cost of United States. A silent site polymorphism at Ugp and an amino acid polymorphism at Treh showed clinal variation. The derived alleles of both genes increased in frequency with latitude, a pattern consistent with temperate adaptation. The Ugp alleles had significantly different activity levels, however Treh alleles did not show significant activity variation.;The role of trehalase in trehalose metabolism was further studied with P-element derived knockout alleles that differed only in their relative levels of trehalase activity. Significant interactions between the trehalase activity and the maximum activities of udp-glucose pyrophosphorylase, phosphoglucomutase, hexokinase and concentrations of glycogen and trehalose are found.;The observations suggest that there is enzyme activity connection between the steps leading to the glycogen and trehalose metabolism. Alterations in trehalose and glycogen metabolites can only be accomplished trough a pathway response involving multiple steps. |
