Data from: The comparative hydrodynamics of rapid rotation by predatory appendages

Countless aquatic animals rotate appendages through the water, yet fluid forces are typically modeled with translational motion. To elucidate the hydrodynamics of rotation, we analyzed the raptorial appendages of mantis shrimp (Stomatopoda) using a combination of flume experiments, mathematical modeling and phylogenetic comparative analyses. We found that computationally efficient blade-element models offered an accurate first-order approximation of drag, when compared with a more elaborate computational fluid-dynamic model. Taking advantage of this efficiency, we compared the hydrodynamics of the raptorial appendage in different species, including a newly measured spearing species, Coronis scolopendra. The ultrafast appendages of a smasher species (Odontodactylus scyllarus) were an order of magnitude smaller, yet experienced values of drag-induced torque similar to those of a spearing species (Lysiosquillina maculata). The dactyl, a stabbing segment that can be opened at the distal end of the appendage, generated substantial additional drag in the smasher, but not in the spearer, which uses the segment to capture evasive prey. Phylogenetic comparative analyses revealed that larger mantis shrimp species strike more slowly, regardless of whether they smash or spear their prey. In summary, drag was minimally affected by shape, whereas size, speed and dactyl orientation dominated and differentiated the hydrodynamic forces across species and sizes. This study demonstrates the utility of simple mathematical modeling for comparative analyses and illustrates the multi-faceted consequences of drag during the evolutionary diversification of rotating appendages.无数水生动物通过在水中旋转附肢实现运动，但目前流体力的建模通常仅考虑平动运动。为阐明旋转运动的流体动力学机制，我们结合水槽实验、数学建模与系统发育比较分析，对螳螂虾（口足目，Stomatopoda）的掠食性附肢开展了研究。相较于更为精细的计算流体动力学模型（computational fluid-dynamic model），计算效率更高的叶素模型（blade-element models）可对阻力提供精准的一阶近似结果。借助该模型的高效性，我们对不同物种的掠食性附肢流体动力学特征开展了对比分析，涵盖新测定的穿刺型物种Coronis scolopendra。粉碎型物种雀尾螳螂虾（Odontodactylus scyllarus）的超快速附肢尺寸小一个数量级，但其承受的阻力矩数值却与穿刺型物种带纹条虾蛄（Lysiosquillina maculata）相近。指节（dactyl）是附肢末端可张开的刺击节段，在粉碎型物种中会产生显著的额外阻力，但在以该节段捕捉逃逸猎物的穿刺型物种中则无此现象。系统发育比较分析结果显示，无论捕食方式为粉碎还是穿刺，体型更大的螳螂虾攻击速度均更慢。综上，阻力受附肢形状的影响极小，而体型、运动速度与指节朝向则是决定并区分不同物种、不同体型个体流体动力的核心因素。本研究证实了简易数学建模在比较分析中的应用价值，并阐明了旋转附肢在进化分化过程中阻力产生的多维度影响。