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

Stanford University, Stanford CA

Investigators

Abstract

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.