Gemmell Brad J, Colin Sean P, Costello John H, Sutherland Kelly R
Department of Integrative Biology, University of South Florida, Tampa, FL 33620, USA.
Whitman Center, Marine Biological Laboratory, Woods Hole, MA 02543, USA.
R Soc Open Sci. 2019 Mar 20;6(3):181615. doi: 10.1098/rsos.181615. eCollection 2019 Mar.
Gelatinous zooplankton exhibit a wide range of propulsive swimming modes. One of the most energetically efficient is the rowing behaviour exhibited by many species of schyphomedusae, which employ vortex interactions to achieve this result. Ctenophores (comb jellies) typically use a slow swimming, cilia-based mode of propulsion. However, species within the genus have developed an additional propulsive strategy of rowing the lobes, which are normally used for feeding, in order to rapidly escape from predators. In this study, we used high-speed digital particle image velocimetry to examine the kinematics and fluid dynamics of this rarely studied propulsive mechanism. This mechanism allows to achieve size-adjusted speeds that are nearly double those of other large gelatinous swimmers. The investigation of the fluid dynamic basis of this escape mode reveals novel vortex interactions that have not previously been described for other biological propulsion systems. The arrangement of vortices during escape swimming produces a similar configuration and impact as that of the well-studied 'vortex rebound' phenomenon which occurs when a vortex ring approaches a solid wall. These results extend our understanding of how animals use vortex-vortex interactions and provide important insights that can inform the bioinspired engineering of propulsion systems.
凝胶状浮游动物展现出多种推进式游泳模式。其中能量效率最高的一种是许多钵水母物种所表现出的划水行为，它们利用涡旋相互作用来实现这一结果。栉水母通常采用基于纤毛的缓慢游泳推进模式。然而，该属中的一些物种已经发展出一种额外的推进策略，即摆动通常用于进食的叶瓣来迅速逃离捕食者。在这项研究中，我们使用高速数字粒子图像测速技术来研究这种鲜为人知的推进机制的运动学和流体动力学。这种机制使（该属物种）能够达到与体型相匹配的速度，几乎是其他大型凝胶状游泳者速度的两倍。对这种逃逸模式的流体动力学基础的研究揭示了新颖的涡旋相互作用，这在其他生物推进系统中尚未被描述过。逃逸游泳时涡旋的排列产生了一种与经过充分研究的“涡旋反弹”现象类似的构型和影响，“涡旋反弹”现象发生在涡旋环接近固体壁时。这些结果扩展了我们对动物如何利用涡旋 - 涡旋相互作用的理解，并提供了重要的见解，可为推进系统的仿生工程提供参考。
