SELECTION FOR LONGEVITY CONFERS RESISTANCE TO LOW-TEMPERATURE STRESS IN DROSOPHILA-MELANOGASTER

One theory of the evolution of longevity says that improvement in life span is dependent on an increased ability to resist environmental str esses of all kind Selective breeding of Drosophila melanogaster popula tions for longevity has demonstrably increased life span and also alte red a number of other traits, such as resistance to starvation, desicc ation, and ethanol fumes, and the ability to sustain longer flight. Wh ile the exact physiologic basis of some of these traits is not yet ful ly understood, at least some are known to derive from the properties o f metabolic substrates of glycolysis. Improvement in those characters can depend partially, therefore, on altered stores of metabolites crea ted from glycogen. Based on the known general relationship of some tra its and the suspected basis in metabolism of others, we examine tile p ossibility here that increased life span is accompanied by other trait s that also confer physiologic resistance to stress. Specifically, we test the prediction that long-lived populations of fruit flies should be more resistant to low (prefreezing) and freezing temperature extrem es. Both selected and control populations were found to be susceptible to prefreezing (1.5 degrees C) and freezing temperatures (0 degrees C ) here, but adults and pupae of the long-lived populations generally s urvived better in both situations, and at all durations of exposure. T he resistance of individuals improved with acclimatization, but was su perior in the long-lived populations whether thermal decline was rapid or stepwise. Cold resistant, long-lived populations also had signific antly higher in vitro levels of glycerol, a cryoprotectant metabolite produced from glycogen. However, while adults and pupae of long-lived stocks were more resistant to cold, larvae of those stocks were more s ensitive and survived relatively poorly at every length of exposure an d acclimation. This surprising result implies that larvae maintain low er levels of cryoprotectant substances. Upon becoming pupae, however, stage-specific capabilities for environmental resistance and long life emerge. This conclusion agrees with a prior study of these stocks ind icating that the uptake and use of nutrients in developing larvae are restricted in long-lived populations.