Collaborative Research: The Functional Significance of Divergent Locomotor Muscle Designs In High Performance Fishes

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This award supports investigations and comparisons of locomotor muscle function and design within a single family of large pelagic sharks, the thresher sharks (Alopiidae). All thresher sharks are easily recognized by their very long caudal fin, which serves for both forward thrust production and prey capture, however, recent work has shown that both the architecture of the swimming muscles and the vascular layout of the common thresher (Alopias vulpinus) is surprisingly distinct from that of the other two species (bigeye thresher, A. superciliosus, and pelagic thresher, A. pelagicus). In the common thresher the red, aerobic locomotor muscle (RM) is condensed into a solid piston-like muscle mass that is predominantly distributed over the anterior body in a medial position (i.e., near the vertebral column). Common threshers also differ from the other two species in having a vascular supply to the RM through a set of lateral vessels that give rise to a counter current heat exchange system. This heat exchange system allows the RM to conserve metabolically produced heat and be warmer than ambient temperature (i.e., regional endothermy). The Alopiidae is the only group known to possess both regionally endothermic and ectothermic taxa, and constitutes the ideal system for testing hypotheses on the evolution of divergent locomotor mechanisms. The researchers will examine the swimming biomechanics and kinematics, thermal physiology, and metabolic biochemistry in the three alopiid sharks. In particular, experiments are designed to determine how the locomotor muscles in the common thresher shark function during steady swimming, and to assess the degree to which the locomotor systems have diverged within a single group of closely-related sharks. Further, the striking similarities in RM morphology between tunas, lamnids, and the common thresher also provide an opportune platform for launching comparative studies that assess the degree to which all three of these groups have converged on a similar mechanical design for swimming. The intellectual merits of this project arise from the unprecedented opportunity to work with a poorly understood group of sharks and collect data on their swimming biomechanics, thermal physiology, musculotendinous adaptations, and the locomotor muscle contractile function. The proposed work will increase the understanding of how selective pressures may have sculpted two divergent muscle systems within the threshers sharks and how these pressures have affected the ecology and biology of this poorly understood group. The broader impacts of this work include participation of under-represented minority scientists, training of undergraduate and graduate students, development of a website for dissemination of research findings, and collaboration with, and outreach to commercial fishermen.