Are diatoms chemically or mechanically defended against protist grazers?

在最近的地质时代，硅藻已经进化成为海洋中最成功的浮游植物分类之一，估计占海洋初级产量的40%。硅藻经常经历的持续繁殖是导致其高初级产量的一个属性。是什么让如此多的硅藻细胞逃脱了浮游动物的捕食压力，而浮游动物每天都会从海洋中清除大多数其他浮游植物？最近，人们假设化学和机械防御都能阻止食草动物，否则它们可能会吃掉硅藻。由C20脂肪酸产生的反应性多不饱和醛（PUAs）在硅藻损伤后已被证明可以抑制许多海洋生物的细胞过程。当成年桡足类动物被喂食富含产聚苯甲酸硅藻的食物时，它们不会受到影响。然而，它们的生殖潜力可能在许多方面受到损害，包括产蛋量减少、孵化成功率降低和幼虫存活率差。因此，这种“潜伏”的化学防御似乎是通过减少后代桡足类动物的放牧影响来发挥作用的。硅藻壳也被假设为通过机械地保护细胞——就像盔甲一样——来抵御某些类型的消费者，从而减少捕食。有初步迹象表明，微型浮游动物，主要是原生生物，通常比甲壳类浮游动物吃更多的硅藻，这可能为硅藻防御的进化提供了选择压力。本研究将包括一系列实验，以测试硅藻对几种以硅藻为食的原生生物（包括异养鞭毛藻和大纤毛虫）的放牧和繁殖的防御能力。硅藻在不同生长条件下产生的多聚苯胺将使用最近开发的气相色谱-质谱技术进行测量。将比较原生生物的放牧、消化和生长速度，并将其饲喂产生不同水平PUAs的密切相关硅藻菌株。荧光探针将用于评估受影响的原生食草动物的细胞损伤模式。为了测试机械防御，我们将硅藻生长在不同水平的硅酸可用性下，以产生不同的气孔厚度，然后评估其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（以及整个海洋）初级生产的调控，以及海洋浮游生物中植物防御途径进化的基本生态问题。更广泛的影响：本项目将通过三个项目直接让本科生参与研究。在俄勒冈州立大学，将招收荣誉学院的化学专业学生参与本研究的有机化学方面的研究。在SPMC， SPMC夏季REU项目的本科生和来自海洋科学本科项目（MIMSUP）的少数民族学生将参与该项目的植物和微型浮游动物实验方面。资金包括支持一名或多名WWU研究生的研究。科学发现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.