Flexible Joints in Rigid Seaweeds: Applying Mechanical Theory to the Convergent Evolution of Articulated Coralline Algae

被海浪冲刷的海岸是地球上水动力压力最大的栖息地。尽管如此，它们支持多样化的海藻组合，这些海藻利用灵活性减少暴露在水流中的面积，并呈现流线型。然而，灵活性在藻类设计进化中的作用很难证明，因为很少有海藻变成化石。相比之下，珊瑚藻用碳酸钙加固细胞壁，因此有广泛的化石记录。在三个不同的例子中，珊瑚进化出了“关节”，这使得它们原本僵硬的叶子具有灵活性。这种经过三次进化的机械创新非常成功，如今的关节珊瑚在海浪肆虐的环境中茁壮成长。这个项目使用生物力学理论来检验这种明显趋同的进化创新的基础和含义。在有机体层面上，操纵藻叶硬度的实验将记录柔性在调节波浪力中所起的作用。最优设计的工程理论将允许确定这些海藻接近最优的程度。在组织水平上，对关节机械性能的测量将揭示三种珊瑚谱系是否在一套共同的材料特性上趋同，以及这些特性如何有助于生存。电子显微镜和各种化学测试将探索珊瑚细胞壁的分子结构，以及这些分子如何排列以产生关节不同寻常的机械性能。总之，这些测量结果提供了一个独特的视角，让我们了解在海洋与海岸相遇的动态环境中，进化是如何影响机械设计的。这里开发的实验室技术将被研究生和PI用于向斯坦福大学的本科生教授生态学、进化论和生物力学原理，并作为研究生强化课程的一部分，迄今已有来自13个国家的学生参加了该课程。这项拨款通过为K-12学生和公众进行实地考察、实验室和开放日，传播对藻类和进化概念的认识和理解。

Wave-swept shores are the most hydrodynamically stressful habitat on Earth. Nonetheless, they support a diverse assemblage of seaweeds, which use flexibility to reduce the area they expose to flow and to assume streamlined shapes. The role of flexibility in the evolution of algal design has been difficult to demonstrate, however, because few seaweeds are fossilized. In contrast, coralline algae reinforce their cell walls with calcium carbonate, and therefore have an extensive fossil record. In three separate instances, corallines evolved "joints," which gave flexibility to their otherwise rigid fronds. This thrice-evolved mechanical innovation has been highly successful, and present-day jointed corallines thrive in wave-swept environments. This project uses biomechanical theory to examine the basis for, and implications of, this apparently convergent evolutionary innovation. At the organismal level, experiments manipulating the stiffness of algal fronds will document the role flexibility plays in modulating wave forces. Engineering theory on optimal design will allow the determination of how closely these seaweeds approach optimality. At the tissue level, measurements of the mechanical properties of joints will reveal if the three coralline lineages have converged on a common set of material properties, and how these properties contribute to survival. Electron microscopy and a variety of chemical tests will explore the molecular structure of coralline cell walls and how these molecules are arranged to produce joints' unusual mechanical properties. Together, these measurements provide a unique look at how evolution affects mechanical design in the dynamic environment where sea meets shore. Laboratory techniques developed here will be used by graduate students and the PI to teach principles of ecology, evolution, and biomechanics to Stanford undergraduates and as part of an intensive graduate course, which to date has been attended by students from 13 countries. This grant spreads awareness and understanding of algae and evolutionary concepts by conducting field trips, labs, and open houses for K-12 students and the public.