WALKER, Jeffrey A.*; SIMONS, Rachel S.; WEBER, Kenneth E.; Univ. Southern Maine, Portland: Selection for increased flight performance in Drosophila melanogaster

A selection experiment on �upwind flight ability� in Drosophilia melanogaster has inadvertently created an elegant system to study the constraints on the evolution of muscle performance. Selected flies have increased their �mean apparent flight speed� from <10 to >220 cm/s over 300 generations of selection. However, comparisons of free flight in still air by James Marden showed no difference in maximum flight speeds between selected and control lines but did show higher average flight speeds and a higher frequency of more horizontal flights. These differences, in combination with the apparent selection for both an attraction to the light at the end of the tunnel and a decreased hunker-down response to wind could explain the evolved increase in �mean apparent flight speed.� Using high-speed video, we found that flies make upwind progress in the compartmentalized wind tunnel by a series of short, burst flights and not by a single, long flight. To test the model that maximum flight performance has not responded to selection, we tested for burst-flight performance differences between selected and control lines by measuring the highest wind speed against which a fly could burst at least 5 cm off of a downwind screen. Selected flies could burst against 40% (males) and 37% (females) higher wind speeds, demonstrating that selection increased maximum flight performance. High-speed films of the burst behavior suggest that at least part of the failure to fly against the wind may be a function of the ability to rotate and stabilize the body into its fast-forward flight position. Mean mass is 32% larger in selected flies. We do not know if the selected flies achieve higher flight speeds by simply adding more muscle or if there been selection on musculoskeletal design to achieve higher mass specific muscle power or to increase control of maneuverability and stability.