Collaborative Research: Are diatoms chemically or mechanically defended against protist grazers?

在地质学上，硅藻已经进化成海洋中最成功的浮游植物种类之一，估计占海洋初级生产力的40%。硅藻经常经历的持续水华是导致它们高初级生产量的一个属性。是什么让这么多硅藻细胞逃脱了浮游动物的捕食压力，这种压力每天都会把大多数其他浮游植物从海洋中带走？最近，化学和机械防御都被认为是为了阻止食草动物，否则它们可能会吃掉硅藻。由C20脂肪酸衍生的反应性多不饱和醛(PUA)在硅藻损伤时被证明在许多海洋生物中抑制细胞过程。当成年的桡足类被喂以富含PUA硅藻的食物时，它们不会受到影响。然而，它们的繁殖潜力可能在许多方面受到损害，包括产卵量减少，孵化成功率降低，幼虫存活率低。因此，这种“隐蔽的”化学防御似乎是通过减少桡足类后代的捕食影响而发挥作用的。硅藻圆锥体还被认为是通过机械地防御细胞--充当盔甲--来减少捕食，以抵御特定类型的消费者。有初步迹象表明，微型浮游动物，主要是原生动物，往往比甲壳类浮游动物捕食更多的硅藻产品，并可能为硅藻防御系统的进化提供选择性压力。这项研究将包括一系列实验，以测试硅藻对捕食和繁殖的几个分类群的硅藻防御能力，包括异养的甲藻和大型纤毛虫。利用最新开发的GC-MS技术，将测量硅藻在不同生长条件下产生PUA的情况。当喂食产生不同水平PUA的密切相关的硅藻菌株时，原生生物的放牧、消化和生长速度将被比较。荧光探针将被用来评估受影响的原生动物食草动物的细胞损伤模式。为了测试机械防御能力，我们将在不同水平的硅酸有效性下培养硅藻，以产生不同的锥体厚度，然后评估它们的原生食草动物的放牧、消化和生长速度。这项研究将有助于我们理解硅藻(因此是海洋)初级生产力的规律，以及关于海洋浮游生物中植物防御途径进化的基本生态学问题。广泛影响：该项目将通过三个项目直接吸引本科生参与研究。在俄亥俄州立大学，来自荣誉学院的化学方向的学生将被招募参与这项研究的有机化学方面。在SPMC，SPMC夏季REU项目的本科生和少数族裔海洋科学本科生项目(MIMSUP)的学生将参加该项目的浮游植物和微型动物实验。基金包括支持一名或多名WWU研究生的研究。科学成果将通过参加国家会议和在同行评议的期刊上发表来广泛传播。

In geologically recent times, diatoms have evolved to become one of the most successful phytoplankton taxa in the sea, responsible for an estimated 40% of marine primary production. The sustained blooms that diatoms often experience are one attribute leading to their high primary production. What allows so many diatom cells to escape the zooplankton grazing pressure that removes most other phytoplankton from the sea on a daily basis? Recently, both chemical and mechanical defenses have been hypothesized to deter grazers that might otherwise consume diatoms. Reactive polyunsaturated aldehydes (PUAs) derived from C20 fatty acids upon diatom wounding have been shown to inhibit cellular processes in numerous marine organisms. When adult copepods are fed a diet rich in PUA-producing diatoms they are unaffected. However, their reproductive potential can be impaired in a number of ways, including decreased egg production, reduced hatching success, and poor survival of larvae. This 'insidious' chemical defense thus appears to function by reducing grazing impacts of subsequent generations of copepods. The diatom frustule has also been hypothesized to reduce predation by mechanically defending the cell - acting as armor - against certain types of consumers. There is preliminary indications that microzooplankton, primarily protists, often graze substantially more diatom production than do crustacean zooplankton, and might provide selective pressure for the evolution of diatom defenses. This research will consist of a series of experiments to test diatom defenses against grazing and reproduction by several taxa of diatom-feeding protists, including heterotrophic dinoflagellates and large ciliates. The production of PUAs by diatoms under different growth conditions will be measured using recently developed GC-MS techniques. Protist grazing, digestion and growth rates will be compared when fed closely related strains of diatoms that produce different levels of PUAs. Fluorescent probes will be used to assess modes of cell damage in affected protist grazers. To test mechanical defenses, we will grow diatoms under different levels of silicic acid availability to generate different frustule thicknesses, and then assess grazing, digestion and growth rates of their protist grazers. This research will contribute to our understanding of the regulation of diatom (and hence total marine) primary production, as well as to fundamental ecological questions about the evolution of plant defense pathways in the marine plankton.Broader Impacts:This project will directly involve undergraduate students in research through three programs. At OSU, chemistry-oriented students from the Honor College will be recruited to participate in the organic chemistry aspects of this research. At SPMC, undergraduate participants in SPMC's summer REU program and ethnic minority students from the Minorities in Marine Science Undergraduate Program (MIMSUP) will participate in phyto- and microzooplankton experimental aspects of the project. Funds are included to support the research of one or more WWU graduate students. Scientific findings will be disseminated broadly though participation in national meetings and publication in peer-reviewed journals.