Dudley 9603736 Inherent limits to exercise performance an athletic capacity of animals are little-understood. For animal locomotion generally, the highest known rates of aerobic metabolism are found in flying forms, particularly among hummingbirds and insects. Dr. Dudley will examine the physiological and biomechanical limits to flight performance in hummingbirds and in insects of comparable body mass. Oxygen concentration and air density of experimental gas mixtures will be simultaneously variesd so as to aerodynamically and physiologically challenge hovering hummingbirds and moths. The limits to flight performance will be evaluated behaviorally by determining the air densities and oxygen concentration at which these animals can no longer sustain hovering flight. Simultaneous measurements of oxygen consumption will evaluate the associated maximal metabolic rates, while aerodynamic models will be applied to the observed wingbeat kinematics to estimate the associated expenditure of mechanical power by the flight muscle. An additional series of experiments will then be implemented that provide enhanced oxygen availability at equivalent air densities, so as to test the hypothesis that diffusive oxygen flux is the limiting step in maximum aerobic performance of these two taxa. Increased rates of oxygen consumption under such conditions will indicate that diffusive constraints limit maximum locomotor performance, whereas no such increase will suggest limits of convective flux within the respiratory system, or biomechanical constraints on flight mechanics. The null hypothesis predicts that the tracheal respiration of moths will ultimately be limited by oxygen availability, whereas the pulmonary-based ventilation of hummingbirds will show no such energetic enhancement under conditions of increased oxygen availaility. More generally, this research will demonstrate inherent design constraints of both vertebrate and insect resporatory systems under conditions of maximum performance.
