FEUERBACHER, ERICA N*; DICKINSON, MICHAEL H: Effects of ambient light level on free-flight behavior of Drosophila melanogaster.

Natural populations of organisms experience several orders of magnitude differences in ambient light level through the course of the day. Both spatial and temporal visual resolution depend on light level, suggesting that light level and organisms? ability to adapt to different light levels may have important implications for the fitness of organisms foraging and seeking mates in natural environments. We investigated the effects of varying light levels on the free-flight behavior of Drosophila melanogaster. Based on current models of flight physiology and aerodynamics, we predicted that flies should favor a particular speed during searching behavior. However, because flight speed is under visual control, and, hence, influenced by light conditions, such as luminance and contrast, flight speed may vary with light level. To test whether flies can compensate for changes in light level, flies were either dark adapted, and flown at one of four light levels, adapted to the light level at which they flew, or adapted to one of the four light levels and flown at a different light level. Using 3-D reconstructions of flight trajectories, we were able to measure horizontal and vertical velocities as well as location and angular velocity of rapid collision avoidance turns, or saccades. When flies were dark adapted, horizontal velocity, altitude, and distance from the center of the arena all increased with increasing light levels, indicating that flight behavior is indeed influenced by variable luminance. However, when flies were adapted to high light levels and subsequently flown in high ambient light, their flight velocity was similar to dark adapted flies flying at low light levels, suggesting that adaptation may play a role in allowing the fly to return to its favored flight velocity.