Acute and chronic effects of atmospheric oxygen on the feeding behavior of Drosophila melanogaster larvae

All insects studied to date show reduced growth rates in hypoxia. Drosophila melanogaster reared in moderate hypoxia (10kPa PO₂) grow more slowly and form smaller adults, but the mechanisms responsible are unclear, as metabolic rates are not oxygen-limited. It has been shown that individual fruit flies do not grow larger in hyperoxia (40kPa PO₂), but populations of flies evolve larger size. Here we studied the effect of acute and chronic variation in atmospheric PO₂ (10, 21, 40kPa) on feeding behavior of third instar larvae of D. melanogaster to assess whether oxygen effects on growth rate can be explained by effects on feeding behavior. Hypoxic-reared larvae grew and developed more slowly, and hyperoxic-rearing did not affect growth rate, maximal larval mass or developmental time. The effect of acute exposure to varying PO₂ on larval bite rates matched the pattern observed for growth rates, with a 22% reduction in 10kPa PO₂ and no effect of 40kPa PO₂. Chronic rearing in hypoxia had few effects on the responses of feeding rates to oxygen, but chronic rearing in hyperoxia caused feeding rates to be strongly oxygen-dependent. Hypoxia produced similar reductions in bite rate and in the volume of tunnels excavated by larvae, supporting bite rate as an index of feeding behavior. Overall, our data show that reductions in feeding rate can explain reduced growth rates in moderate hypoxia for Drosophila, contributing to reduced body size, and that larvae cannot successfully compensate for this level of hypoxia with developmental plasticity.