Flight Performance and Thermal Tolerance of Flies Acclimated to Hypoxia or Hyperoxia

A recent theory holds that high temperature kills animals by raising the oxygen demand above the oxygen supply. Consequently, animals exposed to hypoxia are more sensitive to heating than those exposed to normoxia or hyperoxia. We hypothesized that animals raised in hypoxia would develop their organs to enhance supply of oxygen, thereby making them less sensitive to heating. Such acclimation would be expressed as greater heat tolerance and better flight performance in individuals raised at lower oxygen concentrations. We raised Drosophila melanogaster from eggs to adults under oxygen concentrations ranging from 10% to 31% and measured two variables to test our hypothesis. The two variables measured were knockdown time at 39.5°C and normoxia (21%) and also flight performance at each of several temperatures (37°C, 39°C, and 41°C) and oxygen concentrations (12%, 21%, and 31%). Flies from all treatments had the same heat tolerance as adults. However, flight performance was greatest for flies raised in hyperoxia, indicating that flies acclimated to oxygen supply during development but in the opposite direction that we predicted. Flight performance was also greatly affected by the temperature, with flies at the highest temperature being less likely to fly than those at lower temperatures. Contrary to current theory, the oxygen concentration during testing did not influence the ability to fly as much as development conditions did. Future research will test the hypothesis that flies that develop in hyperoxic environments fly better because they can grow to a larger size at adulthood.