Physiological Responses to Selection for Desiccation Resistance inDrosophila melanogaster

Abstract

Comparative physiologists and physiological ecologists have striven to elucidate the physiological adaptations which eliminate or mitigate environmental stress. Stress tolerance is thought to influence the distribution of species as well as the fitness of individuals within various habitats. Differential stress tolerance depends in large part on physiological mechanisms which mitigate the deleterious effects of stress. Very little information is available, however, regarding the mechanisms and pathways by which such physiological adaptations arose and were modified. We point out two methods by which one can investigate the evolution of stress tolerance: phylogenetic studies and selection studies. Phylogenetic studies have the advantage that they can be used to study wild populations, with the drawback that species numbers and distribution may be limiting. In addition, for many physiologically interesting clades, the phylogenetic relationships have yet to be determined. Selection studies have the advantage that the evolution of physiological systems can be studied in response to very specific forms of stress. In addition, the phytogeny of the organisms can be experimentally manipulated and replication permits rigorous statistical analysis. The results of studies of the evolution of increased desiccation resistance in Drosophila are presented as an example of the methods by which insights can be obtained regarding the variables which respond to selection, the rate of evolutionary change and the process by which physiological performance changes over evolutionary time. Selection studies can be designed to provide models regarding the mechanisms, tuning and directions of physiological evolution.