Combining three mild stresses in Drosophila melanogaster flies does not have a more positive effect on resistance to a severe cold stress than combining two mild stresses.
Among other positive effects, mild stresses can increase resistance to severe stresses. Previous studies combining two mild stresses showed that when each mild stress had positive effects their combination had more positive effects than each mild stress. The present study tested whether combining three mild stresses could still provide positive additive effects, or whether this combination has negative effects because it is no longer a mild stress but rather a strong stress with negative effects. Flies were subjected to either fasting, hypergravity for one or two weeks, or cold shocks, to combinations of two or of the three mild stresses, and survival to a severe cold stress was observed at 13 or 20 days of age. Positive effects of each mild stress and of combining two stresses could be observed, but combining the three stresses provided a similar survival or a lower survival than the combination of two stresses. Thus, combining three stresses was not more efficient than combining two stresses.