Flight

Michael Dickinson

California Institute of Technology

Robert Dudley

University of California, Berkeley

From their first appearance in the late Paleozoic, winged insects have emerged as critical components of nearly all terrestrial ecosystems. Many important behavioral features of insects, including evasion of predators, dispersal, and reproductive strategies, rely in some way on flight behavior. Wings themselves, as cuticular structures, have no intrinsic musculature and are moved instead via thoracic deformations and by muscles that insert directly at the wing base. The back and forth motion of the wing through the wingbeat, as well as the rotation about its longitudinal axis at the beginning and end of each stroke, creates unsteady aerodynamic forces of continuously changing direction and magnitude. Flight control relies on multiple sensory modalities to maintain stable trajectories and to maneuver via bilaterally asymmetric motions of the wings and body. Flight is energetically costly, and the delivery of oxygen to flight musculature is limited by diffusion in the fine branches of the tracheal system. Heat simultaneously produced by contraction of inherently inefficient muscles may be co-opted in the regulation of body temperature during flight to further enhance performance. Forces of both natural and sexual selection have contributed synergistically to the evolution of insect flight performance and maneuverability. Contemporary insect diversity largely comprises extensive radiations of miniaturized species. Flight biomechanics of these small insects is complicated by the viscous nature of airflows and depends in part on the high wingbeat frequencies enabled by a specialized muscle type termed asynchronous muscle. Asynchronous flight muscle has evolved independently more than eight times among the winged insects and enables muscles to generate increased mechanical power by trading sarcoplasmic reticulum for more contractile fibrils and mitochondria. The majority of insect species-level diversity appears to derive indirectly from this flight-related innovation that facilitates miniaturization.

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