Critical oxygen partial pressures and maximal tracheal conductances for Drosophila melanogaster reared for multiple generations in hypoxia or hyperoxia

In Drosophila melanogaster and other insects, increases in atmospheric oxygen partial pressure (aPO2) tend to increase adult body size and decrease tracheal diameters and tracheolar proliferation. If changes in tracheal morphology allow for functional compensation for aPO2, we would predict that higher aPO2 would be associated with higher critical PO2 values (CritPO2) and lower maximal tracheal conductances (Gmax). We measured CritPO2 and Gmax for adult and larval vinegar flies reared for 7-9 generations in 10, 21 or 40 kPa O2. The CritPO2, CO2 emission rates and Gmax values were generally independent of the rearing PO2 these flies had experienced, suggesting that minimal functional changes in tracheal capacities occurred in response to rearing PO2. Larvae were able to continue activity during 20 min of anoxia. The lack of multigenerational rearing PO2 effects on tracheal function suggests that the functional compensation at the whole-body level due to tracheal morphological changes in response to aPO2 may be minimal; alternatively the benefits of such compensation may occur in specific tissues or during processes not assessed by these methods. In larvae, the CritPO2 and the capacity for movement in anoxia suggest adaptations for life in hypoxic organic matter.