9514203 Shadwick The PI proposes that the evolution of animals to maximize swimming efficiency will produce characteristic body shapes, patterns of muscle activity and body movement. Among oceanic animals, the tunas represent one ultimate exploitation of ibis principle. The high-performance swimming of these fish is associated with a suite of adaptations on many levels of organization - from biochemical to behavioral. For example, tunas have a highly streamlined muscular body which is thickened centrally and tapers to a very narrow caudal region just in front of the stiff, crescent-shaped tail fin. This tail acts as a hydrofoil as it is swept back and forth through the water, producing nearly all of the tunas' forward thrust. Unlike other fish, undulations of the body are restricted to the tail region, giving the tunas' propulsive system a relatively high mechanical efficiency. For these reasons, the physiological basis for swimming in tunas is of great interest in the study of aquatic locomotion. The major objective in the PI's investigation is to analyze biomechanical design features of tunas and to synthesize a comprehensive physiological model of how these elite aquatic athletes achieve their high levels of performance. Specifically, this will involve collecting data on the structure and mechanical properties of the muscular and skeletal systems, and analyzing the swimming movements in the context of engineering and fluid mechanics principles. The work will be framed within three scientific hypotheses, one relating to the manner in which muscular contractions along the body act to produce movements in the tail, another relating to the structure and mechanical properties of the connective tissues that transmit the muscle forces to the backbone and ultimately the tail fin, and a third which deals with the timing of muscle activation along the body and how power is generated. These experiments involve studying live fish which are swimming under controlled conditions by use of an aquatic " treadmill" instrument. Information on the timing of muscle activation along the body in relation to the timing and degree of muscle shortening is essential for calculation of muscle power output in swimming fish. In studies on other fish, the amount of muscle shortening and its timing relative to activation by the nervous system has been inferred from shape changes of the body measured by video imaging techniques. In the PI's estimation this approach is inadequate, and in the new studies the PI will make direct measurement of local muscle shortening and activation with ultrasound and electrophysiological methods previously developed by the PI's group. The PI will also characterize the contractile properties of muscle tissue from different parts of the fish body directly, using a oscillatory loading technique that simulates the manner in which the muscle is used by the fish when it swims. Finally, the PI will examine the structures responsible for transmission of muscle forces to the tail fin. These are the connective tissue sheets separating each body segment, the skin and the tendons that link the muscles to the backbone and tail fin. Analysis of the mechanical properties of these tissues will be performed with techniques similar to those used by mechanical engineers to test structural materials. Completion of the studies described in this proposal will allow for the creation of an integrated model of how the various mechanical and physiological elements present in tunas function to provide the high-performance qwimming displayed by these fish. ***
