Flexible joints in rigid seaweeds: structure, mechanics, and convergent evolution in articulated coralline algae

人造建筑物通常是刚性的，通常会被海浪的冲击摧毁，但海藻通过灵活的方式在被海浪席卷的海岸上生存下来。关节珊瑚藻类(海藻的一种)为了解这种灵活性是如何演变的提供了一个特殊的机会。珊瑚藻类有钙化的细胞壁，这使得它们在默认情况下是坚硬的。然而，1亿年前，一些珊瑚进化出关节，这是一项结构创新，使这些新生的灵活藻类得以茁壮成长。事实上，珊瑚海藻的关节进化了三次，显然汇聚在一个共同的柔韧性机械公式上，这可能也使珊瑚能够抵抗通常伴随着柔性结构的疲劳损伤。丹尼的目标是阐明三种铰接珊瑚谱系中每一种的会聚机制，使他能够探索和量化这些藻类达成共同机械解决方案的不同方式。丹尼建议研究所有组织层次的灵活性机制--从关节中细胞壁的异常化学和结构，到关节材料的非凡机械性能，再到整个叶子的结构和动态。如果这项研究证实铰接珊瑚确实能抵抗疲劳破坏，它可能会为抗疲劳仿生材料的开发提供指导，并洞察其他柔性结构的潜在抗疲劳性，包括生物和人造。本研究使用的生物力学方法是教授学生如何跨领域整合知识的理想环境。丹尼使用这种机械观点为斯坦福大学的本科生教授一门课程--《生态学、进化论和植物生物学》，并将与圣地亚哥海洋探索研究所合作，利用生物力学作为K-12贫困学生的教学工具。

Manmade structures, which are typically rigid, are often destroyed by the pounding of ocean waves, but seaweeds survive on wave-swept shores by being flexible. Articulated coralline algae (a type of seaweed) provide an exceptional opportunity to understand how this flexibility evolved. Coralline algae have calcified cell walls, which renders them, by default, rigid. However, 100 million years ago, some corallines evolved joints, a structural innovation that allowed these newly flexible algae to thrive. Indeed, joints evolved three separate times in coralline seaweeds, apparently converging on a common mechanical formula for flexibility that may also have allowed corallines to resist the fatigue damage that commonly accompanies flexible structures. Denny aims to elucidate the mechanics of this convergence in each of the three lineages of articulated corallines, allowing him to explore and quantify the different ways in which these algae have arrived at a common mechanical solution. Denny proposes to examine the mechanics of flexibility at all levels of organization?from the unusual chemistry and structure of cell walls in joints, to the extraordinary mechanical properties of joint materials, to the structure and dynamics of whole fronds. If this research confirms that articulated corallines are indeed resistant to fatigue failure, it may provide guidance for the development of fatigue resistant biomimetic materials and insight into the potential fatigue resistance of other flexible structures, both biological and manmade.The biomechanical approach used in this research is an ideal context in which to teach students how science integrates knowledge across fields. Denny uses this mechanistic perspective to teach a course, "Ecology, Evolution, and Plant Biology," for Stanford undergraduates, and will collaborate with the Ocean Discovery Institute of San Diego to exploit biomechanics as a teaching tool for underprivileged K-12 students.