Collaborative Research: 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类群之一，估计占海洋初级生产的40%。硅藻经常经历的持续开花是导致其高初级生产的一个属性。是什么让这么多的硅藻细胞逃脱了浮游动物的放牧压力，每天从海洋中清除大多数其他浮游植物？最近，化学和机械防御被假设为阻止可能以其他方式消耗硅藻的食草动物。硅藻损伤后C20脂肪酸衍生的反应性多不饱和醛（PUA）已被证明能抑制许多海洋生物的细胞过程。当成年桡足类被喂食富含PUA生产硅藻的食物时，它们不受影响。然而，它们的繁殖潜力可能会以多种方式受损，包括产卵量减少，孵化成功率降低和幼虫存活率低。因此，这种“阴险”的化学防御似乎通过减少后代桡足类的放牧影响来发挥作用。硅藻硅藻壳也被假设为通过机械地保护细胞-充当盔甲-对抗某些类型的消费者来减少捕食。有初步迹象表明，微型浮游动物，主要是原生动物，往往吃更多的硅藻生产比甲壳类浮游动物，并可能提供选择性的压力硅藻防御的演变。这项研究将包括一系列的实验，以测试硅藻防御放牧和繁殖的几个类群的食草原生生物，包括异养甲藻和大型纤毛虫。利用最近开发的GC-MS技术测量硅藻在不同生长条件下产生的PUAs。当喂食产生不同水平PUA的密切相关的硅藻菌株时，将比较原生动物的摄食、消化和生长速率。荧光探针将用于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，我们将在不同水平的草酸可用性下生长硅藻，以产生不同的硅藻壳厚度，然后评估其原生生物食草动物的放牧，消化和生长速率。这项研究将有助于我们了解硅藻（因此总海洋）初级生产的调节，以及有关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，化学导向的学生从荣誉学院将被招募参加有机化学方面的这项研究。在SPMC，SPMC夏季REU项目的本科生和来自海洋科学本科项目少数民族的少数民族学生将参加该项目的植物和微型浮游动物实验。资金包括支持一个或多个WWU研究生的研究。将通过参加国家会议和在同行评审的期刊上发表论文，广泛传播科学研究结果。

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.