GIBBS, Allen G.; VANIER, Cheryl H.; Univ. of Nevada, Las Vegas; Univ. of Nevada, Las Vegas: Evolution of water balance and gene expression in desiccation-selected Drosophila melanogaster

Because of their small size and large surface-area-to-volume ratio, insects face significant problems in maintaining positive water balance. These problems are particularly severe in arid environments such as deserts. To investigate the mechanistic basis of differences in water balance, we subjected replicated populations of Drosophila melanogaster to selection for resistance to desiccation. The major physiological responses were a 30% increase in body size and water storage, a doubling in carbohydrate storage, and a reduction in water-loss rates mediated by reduced activity and respiratory water loss. Over 90% of the variation in desiccation resistance could be explained by differences in carbohydrate storage and water-loss rate. We also used microarrays to identify changes in gene expression patterns in unselected flies which were exposed to desiccation. Over 150 genes exhibited increased or decreased expression, with genes involved in carbon and protein metabolism being over-represented in this set. Evolved changes in expression are currently being investigated. This will allow us to identify genetic targets of selection.