Stress experiments as a means of investigating age-specific mortality in Drosophila melanogaster.

Age-specific mortality rates level off at older ages in genetically homogeneous experimental populations of Drosophila. Here we describe an experiment that is informative about the causes of mortality rate changes. By applying a brief, nondebilitating stress that increases mortality early in life and then observing subsequent mortality trajectories, it is possible to determine whether populations are heterogeneous for factors influencing mortality. We show that 24-h exposure to a desiccating air flow causes a spike and then a decrease in mortality rates in experimental populations compared to controls. If there is no stress-induced enhancement of vitality, then the results demonstrate the existence of heterogeneity for mortality rates in genetically homogeneous populations.