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Published June 30, 2020 | Published
Journal Article Open

Jellyfish and Fish Solve the Challenges of Turning Dynamics Similarly to Achieve High Maneuverability


Turning maneuvers by aquatic animals are essential for fundamental life functions such as finding food or mates while avoiding predation. However, turning requires resolution of a fundamental dilemma based in rotational mechanics: the force powering a turn (torque) is favored by an expanded body configuration that maximizes lever arm length, yet minimizing the resistance to a turn (the moment of inertia) is favored by a contracted body configuration. How do animals balance these opposing demands? Here, we directly measure instantaneous forces along the bodies of two animal models—the radially symmetric Aurelia aurita jellyfish, and the bilaterally symmetric Danio rerio zebrafish—to evaluate their turning dynamics. Both began turns with a small, rapid shift in body kinematics that preceded major axial rotation. Although small in absolute magnitude, the high fluid accelerations achieved by these initial motions generated powerful pressure gradients that maximized torque at the start of a turn. This pattern allows these animals to initially maximize torque production before major body curvature changes. Both animals then subsequently minimized the moment of inertia, and hence resistance to axial rotation, by body bending. This sequential solution provides insight into the advantages of re-arranging mass by bending during routine swimming turns.

Additional Information

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Received: 21 March 2020; Accepted: 28 June 2020; Published: 30 June 2020. We thank S. Spina and C Doller of the New England Aquarium for providing A. aurita and J. Gitlin of the Marine Biological Laboratory for providing Danio rerio used in our experimental work. Author Contributions: All authors conceived the research; S.P.C., B.J.G., M.C.L., and J.H.C. collected animal measurements; all authors analyzed data; J.O.D. and J.H.C. wrote initial manuscript; all authors contributed to revisions. All authors have read and agreed to the published version of the manuscript. Funding for this work was provided by the US National Science Foundation (1511333 to JOD, 1510929 to SPC, 1511996 to BJG, 1511721 to J.H.C.) and the Office of Naval Research (000141712248 to MCL, N00140810654 to J.H.C.). KNL was supported by a National Science Foundation Graduate Research Fellowship under grant DGE-1745303. The authors declare no conflict of interest.

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