Wong J Y, Chan B K K, Chan K Y K
Department of Life Science, National Taiwan Normal University, Taipei 11677, Taiwan.
Biodiversity Program, Taiwan International Graduate Program, Academia Sinica, Taipei 11529, Taiwan.
Integr Org Biol. 2020 Apr 17;2(1):obaa011. doi: 10.1093/iob/obaa011. eCollection 2020.
A central goal in evolutionary biology is connecting morphological features with ecological functions. For marine invertebrate larvae, appendage movement determines locomotion, feeding, and predator avoidance ability. Barnacle larvae are morphologically diverse, and the morphology of non-feeding lecithotrophic nauplii are distinct from those that are planktotrophic. Lecithotrophic larvae have a more globular body shape and simplified appendages when compared with planktotrophs. However, little is known about whether and how such morphological changes affect kinematics, hydrodynamics, and ecological functions. Here, we compared the nauplii kinematics and hydrodynamics of a lecithotrophic Rhizocephalan species, , against that of the planktotrophic nauplii of an intertidal barnacle, . High-speed, micro-particle image velocimetry analysis showed that the nauplii swam faster and had higher amplitude and more synchronous appendage beating than the nauplii. This fast swimming was accompanied by a faster attenuation of induced flow with distance, suggesting reduced predation risk. nauplii had more efficient per beat cycles with less backward displacement during the recovery stroke. This "anchoring effect" resulted from the anti-phase beating of appendages. This movement, together with a high-drag body form, likely helps direct the suction flow toward the ventral food capturing area. In sum, the tradeoff between swimming speed and predation risks may have been an important factor in the evolution of the observed larval forms.
进化生物学的一个核心目标是将形态特征与生态功能联系起来。对于海洋无脊椎动物幼虫来说，附肢运动决定了其运动、摄食和躲避捕食者的能力。藤壶幼虫在形态上具有多样性，非摄食性的卵黄营养型无节幼虫的形态与浮游生物营养型的不同。与浮游生物营养型幼虫相比，卵黄营养型幼虫的身体形状更呈球形，附肢也更简化。然而，对于这种形态变化是否以及如何影响运动学、流体动力学和生态功能，人们却知之甚少。在这里，我们将一种卵黄营养型根头目物种的无节幼虫的运动学和流体动力学与一种潮间带藤壶的浮游生物营养型无节幼虫进行了比较。高速微粒子图像测速分析表明，该根头目物种的无节幼虫比潮间带藤壶的无节幼虫游得更快，附肢摆动的幅度更大且更同步。这种快速游动伴随着诱导流随距离的更快衰减，这表明捕食风险降低。该根头目物种的无节幼虫每搏动周期更高效，在恢复冲程期间向后的位移更小。这种“锚定效应”是由附肢的反相摆动产生的。这种运动，再加上高阻力的身体形态，可能有助于将吸入流导向腹部的食物捕获区域。总之，游泳速度和捕食风险之间的权衡可能是观察到的幼虫形态进化中的一个重要因素。
