FOLK, D.G.; BRADLEY, T.J.; Univ. of California, Irvine; Univ. of California, Irvine: Water Balance and Ion Regulation in Drosophila melanogaster Selected For Enhanced Desiccation Resistance

A formidable and ubiquitous threat to terrestrial animals is that of desiccation. To study the strategies accessible to insects in resisting this threat and maintaining water balance, five populations of Drosophila melanogaster were placed under selection for enhanced desiccation resistance. For each population selected for resistance to desiccation, a control population has been maintained under identical conditions, except the control flies have had uninterrupted access to water. The adaptive responses to selection for enhanced desiccation resistance are multifold and include a very large hemolymph pool, which acts to protect intracellular volume during periods of water stress. One consequence of the increased hemolymph volume in hydrated flies is an increase in hemolymph sodium content. During extended periods of desiccation, when hemolymph volume is continually lost, the flies must either face the dangers of a rising extracellular sodium concentration or employ some strategy to adjust sodium levels. We describe the strategies employed by the desiccation-resistant flies in regulating sodium (and chloride) content during periods of significant water loss. We have also investigated the capacity of the desiccation-resistant flies to recover following a sublethal bout of desiccation. Our findings indicate that, in response to the prescribed selection pressures, the desiccation-resistant flies have evolved an improved capacity to restore certain somatic components, namely sodium content, water volume, and dry mass, which are reduced during desiccation. A crucial outcome of recovery from desiccation stress in these flies is the restoration of desiccation resistance. Funded by NSF Grant IBN 0079501.