FOLK, D.G.*; BRADLEY, T.J.: Ion Regulation and Water Balance in Drosophila melanogaster Selected for Enhanced Desiccation-Tolerance

We are examining physiological processes associated with increased resistance to desiccation in five, replicate populations of Drosophila melanogaster that have undergone laboratory selection for enhanced desiccation-tolerance. For each population of desiccation-resistant flies (D populations), we have maintained a control population (C populations) under identical conditions, except that the control flies have had uninterrupted access to water. In previous studies we found that increased resistance to desiccation in the D populations is associated with a more than three-fold increase in hemolymph volume, relative to controls. Presumably, the hemolymph acts as a water reservoir that can be tapped to replace cellular water that is lost during dehydration, thus during a bout of desiccation the volume of the hemolymph falls. As hemolymph volume is reduced, the insects can employ one of three osmotic strategies: they can 1) allow the hemolymph osmotic concentration to rise, 2) excrete solutes to achieve osmoregulation, or 3) sequester solutes within the body. We are currently examining the strategies used by the selected and control populations and will report on the regulation of sodium, potassium, and chloride during desiccation in these populations. We are particularly interested in determining those aspects of osmoregulation that have evolved to provide enhanced desiccation-tolerance. Funded by NSF Grant IBN 0079501.