Changes in size strongly influence organisms' ecological performances. For aquatic organisms, they can transition from viscosity- to inertia-dominated fluid regimes as they grow. Such transitions are often associated with changes in morphology, swimming speed and kinematics. Barnacles do not fit into this norm as they have two morphologically distinct planktonic larval phases that swim differently but are of comparable sizes and operate in the same fluid regime (Reynolds number 100–101). We quantified the hydrodynamics of the rocky intertidal stalked barnacle Capitulum mitella from the nauplius II to cyprid stage and examined how kinematics and size increases affect its swimming performance. Cyprids beat their appendages in a metachronal wave to swim faster, more smoothly, and with less backwards slip per beat cycle than did all naupliar stages. Micro-particle image velocimetry showed that cyprids generated trailing viscous vortex rings that pushed water backwards for propulsion, contrary to the nauplii's forward suction current for particle capture. Our observations highlight that zooplankton swimming performance can shift via morphological and kinematic modifications without a significant size increase. The divergence in ecological functions through ontogeny in barnacles and the removal of feeding requirement likely contributed to the evolution of the specialized, taxonomically unique cyprid phase.

中文翻译：

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藤壶幼虫整个发育过程中的游泳运动学和流体动力学

大小的变化强烈影响生物体的生态性能。对于水生生物来说，它们在生长过程中可以从粘度主导的流体状态转变为惯性主导的流体状态。这种转变通常与形态、游泳速度和运动学的变化相关。藤壶不符合这一标准，因为它们有两个形态不同的浮游幼虫阶段，游动方式不同，但大小相当，并且在相同的流体状态下运行（雷诺数 100-101）。我们量化了岩石潮间带茎藤壶 Capitulum mitella 从无节幼体 II 到鲤鱼阶段的流体动力学，并研究了运动学和尺寸增加如何影响其游泳性能。与所有无节幼体阶段相比，鲤鱼以异时波拍打它们的附肢，从而游得更快、更平稳，并且每个节拍周期向后滑动更少。微粒图像测速表明，鲤鱼产生尾随的粘性涡环，将水向后推以进行推进，这与无节幼体用于捕获颗粒的向前吸流相反。我们的观察强调，浮游动物的游泳性能可以通过形态和运动学的改变而改变，而不会显着增加体型。藤壶的个体发育和摄食需求的消除所导致的生态功能的分歧可能导致了特殊的、分类学上独特的鲤鱼阶段的进化。