Flap, flutter, and flow: morphological adaptation of marine macroalgae under hydrodynamic stress

潮间带被海浪席卷的岩石海岸是地球上身体压力最大的栖息地之一。在退潮时，海藻暴露在陆地条件下，必须抵抗温度和干燥压力。在涨潮时，破碎的海浪会施加水动力，可能会破坏或驱赶岩石上的藻类。尽管有这种逆境，岩石海岸还是支持着丰富的、形态多样的大型藻类群落。 我的研究项目探索海藻对物理应激源的生物力学、形态和生理适应，如波浪诱导的阻力。大多数大型藻类生活在水动力压力很大的栖息地，形成“随波逐流”的柔性菌体，许多物种可以调整菌体形态以适应环境条件。目前提案中的实验在多个分析尺度上测试对水动力压力的适应性，从细胞壁化学到组织组成，再到整个生物体的表现。实验将探索被海浪扫荡的大型藻类中新结构的进化。例如，我们将研究钙化壳类祖先的直立节叶的反复进化，使其他钙化的菌体具有灵活性，以及棕色大型藻类中浮力结构的反复进化，以补偿组织降解和移位。通过化学、结构和生物力学的比较，我们将确定这些生态重要特征的平行进化机制。其他实验将探索大型藻类进化过程中形态和生理之间的权衡。例如，我们已经证明，分枝海藻具有更大的阻力，必须比未分枝海藻更牢固地附着在基质上，以避免移位。通过从真实的海藻中切出不同形状的海藻，但保持光合作用表面积不变，我们将检验这一假设，即分枝也可以增加光合作用和流动中的养分交换，以补偿生物机械成本。进一步的实验将研究流动中形态可塑性的驱动因素以及未来气候压力下生物力学适应的限制。使用我们最先进的生长水槽，我们将首先在不同的流速下种植海带，以确定它们能够多精确地调整叶片形态以限制阻力。然后，我们将提高温度和溶解二氧化碳浓度，以测试气候胁迫对水流形态响应的影响。这些数据将有助于洞察这些重要的饲料和栖息地海藻在被海浪席卷的栖息地中当前和未来的生存情况。总之，拟议的实验检查了海洋大型藻类的生物力学适应性和功能形态，这些藻类是由物理环境施加的选择压力塑造的。在多个分析尺度上探索一组广泛不同的大型藻类，我的实验室的综合和创新方法试图解释进化是如何协调我们今天看到的海藻惊人的形态多样性的。

The intertidal zone of wave-swept rocky shores is among the most physically stressful habitats on the planet. At low tide, seaweeds are exposed to terrestrial conditions and must resist temperature and desiccation stresses. At high tide, crashing waves impose hydrodynamic forces that threaten to break or dislodge algae from the rocks. Despite this adversity, rocky shores support rich and morphologically diverse communities of macroalgae. My research program explores the biomechanical, morphological and physiological adaptations of seaweeds to physical stressors, such as wave-induced drag force. Living in a hydrodynamically stressful habitat, most macroalgae develop flexible thalli that “go with the flow” and many species can adjust thallus morphology to suit environmental conditions. Experiments in the current proposal test adaptations to hydrodynamic stress at multiple scales of analysis, from cell wall chemistry, through tissue composition, to whole organism performance. Experiments will explore the evolution of novel structures in wave-swept macroalgae. For example, we will investigate the repeated evolution of erect segmented fronds from calcified crustose ancestors, allowing otherwise calcified thalli to be flexible, and the repeated evolution of buoyant structures in brown macroalgae to compensate for tissue degradation and dislodgement. Through chemical, structural, and biomechanical comparisons, we will determine the mechanism of parallel evolution in these ecologically important features. Additional experiments will explore trade-offs between morphology and physiology during macroalgal evolution. For example, we have shown that branched seaweeds experience more drag and must attach more securely to the substratum than unbranched seaweeds to avoid dislodgement. By cutting different shapes out of real seaweeds, but holding photosynthetic surface area constant, we will test the hypothesis that branching also increases photosynthesis and nutrient exchange in flow, compensating for biomechanical costs. Further experiments will investigate the drivers of morphological plasticity in flow and the limits to biomechanical adaptation under future climate stress. Using our state-of-the-art growth flumes, we will first grow kelps at different flow speeds to determine how precisely they are able to adjust blade morphology to limit drag. We will then increase temperature and dissolved CO2 concentration to test the impact of climate stress on the morphological response to flow. These data will lend insight into the current and future survival of these important forage- and habitat-forming seaweeds in wave-swept habitats. In sum, proposed experiments examine the biomechanical adaptations and functional morphologies of marine macroalgae that have been shaped by selective pressures imposed by the physical environment. Exploring a broadly diverse set of macroalgae at multiple scales of analysis, my lab’s integrative and innovative approach seeks to explain how evolution has orchestrated the striking morphological diversity of seaweeds we see today.