FRAZIER, Melanie*; DILLON, Michael; Univ. of Washington; Univ. of Washington: Flying and Walking in Cold, Thin Air

High altitude may be especially challenging for flying insects. They have the highest energy consumption of any organism, but their ability to generate energy could be severely suppressed at altitude by both hypoxia and cold temperatures. Moreover, their wings produce less lift because air density is low. Nevertheless, many insects are abundant in mountains. For example, some fruitflies are found at moderate altitudes (5,123 m; 54% normal air density) where they must actively find food sources and mates. To do so, they must be able to fly and walk in cold, thin air. Our goal was to determine how air density and temperature interactively affect the ability of Drosophila melanogaster to initiate flight and to walk quickly. To assess flight performance, we used a factorial design with five temperatures: 18, 25, 30, 32, 34 &degC and four air densities: 33% (= Mt. Everest summit), 50%, 66%, 100% sea level. The probability of flight was reduced in both low temperatures and low air-densities. In addition flight probability was influenced by an interaction between temperature and air density – flight probability was especially low when cold temperature was combined with low air density. However, air density alone did not limit flight initiation until densities fell below ecologically relevant values (around 50% air density). To measure walking speed we used a factorial design consisting of three temperatures: 18, 25, 30 &degC and four air densities: 33%, 50%, 66%, 100% sea level. Cold temperatures and low air densities reduced walking speed; however, no interaction was evident between temperature and air density. These patterns suggest that the cold and low air density may have synergistic negative effects on flight ability, but not on walking speed.