Variation in atmospheric oxygen levels affects adult insect wing morphology and flight performance

Abstract

Objective and HypothesesChanges in atmospheric oxygen over geologic time have been hypothesized to drive several evolutionary events in the history of insects. However, the insect fossil record is composed of mostly isolated wings, which presents challenges in interpreting the data and testing these hypotheses. Therefore, our objective was to understand how insect wing morphology varies with atmospheric oxygen as a critical first step in addressing these hypotheses. Given that wing veins contain tracheae which have been shown to vary with rearing oxygen elsewhere in the body, we hypothesized that wing vein diameters should be inversely correlated with rearing oxygen and that these changes would affect flight performance of these insects.MethodsDrosophila melanogaster and Blatella germanica were reared from hatching to adults under three different oxygen concentrations: 12% (hypoxia), 21% (normoxia) and 31% (hyperoxia). The wings were then dissected and imaged using a mechanical stage mounted on an inverted microscope. Wing area, wing vein diameters, wing vein lengths, and tracheal diameters were all measured using ImageJ. In a second experiment, flies were again reared in three different oxygen concentrations and then flown in all three oxygen levels to test the effect of these changes in wing morphology on flight performance.ResultsIn both Drosophila and Blatella, mass specific wing area, wing vein diameters, and tracheal diameters were all inversely correlated with rearing oxygen. In terms of flight performance, flies reared in 31% oxygen flew the best. However, overall flies flew the best in the oxygen level they were reared under.ConclusionsThese results demonstrate that rearing oxygen impacts wing morphology in several groups of insects and that these changes in morphology directly impact flight performance. These changes suggest that wing morphology in the fossil record can be used to interpret evolutionary changes. Additionally, this suggests that wing vein diameter may be a potential proxy for atmospheric oxygen over geologic time.