Collaborative research: Investigation of a phytoplankton DMSP-based chemical defense system active against protist grazers

化学防御？个体用于减少或消除死亡因素的化学品种类繁多，分布广泛，对物种间的相互作用很重要。与陆地和海洋底栖物种相比，对水生生物的研究较少，但化学防御被认为在构建水生群落中发挥作用。它们在促进藻华的形成和持续方面可能特别重要。在最近的NSF？支持的研究，我们表明，球石藻Emiliania huxleyi是化学防御对大多数测试原生草食动物物种。至少从E.赫胥黎硫化学被证明可以降低原生动物放牧率：高DMSP裂解酶活性（DLA）和外源DMSP（二甲基磺基丙酸酯）本身。由于高浮游植物DLA和溶解的DMSP都存在于海洋中，我们认为这种防御系统在允许E。huxleyi开花形成并持续存在。此外，作为许多开花？形成甲藻和prymnesiophyte物种具有高的细胞内DMSP浓度，并且至少一些具有高DLA，这种化学防御系统可能对浮游植物水华动态具有广泛的重要性。对DMSP“防御系统”的大量实验表明，DMSP对原生生物没有毒性。相反，这种亚致死防御系统可能是基于食草动物和猎物物种之间的细胞间化学通讯。本文拟对这一防御系统的来源、作用机制和意义进行探讨，并提出一个多层次的防御系统。将进行一级调查。添加高裂解酶E. huxleyi细胞和国防化学品的天然水样和混合实验室组装将允许测试的社区？水平防御效应，包括可能减少微型浮游动物的放牧，放牧转移到其他猎物类型，对其他浮游植物物种的化感作用。人口？水平研究将揭示原生生物对防御的敏感性是否与原生生物分类群、摄食方式或大小有关。在个人和分子水平上，一个光谱的可能性机制DMSP？提出了诱导的摄食抑制。化学线索（DMSP裂解和氧化产物，藻类渗透）对原生动物的摄食率和个人行为的影响将被研究作为一种手段，测试这些possibilities. BROADERIMPACTThe拟议的研究将包括众多的研究生和本科生的参与者，包括学生在香农点海洋中心的少数民族在海洋科学本科课程。其他的推广活动将包括将概念、技术和发现纳入教学活动，并准备针对普通观众的网络和印刷材料。智力优势发展对亚致命化学防御的理解，因为它们涉及细胞信号传导，并最终形成浮游植物水华，这是海洋学、生物科学和教育的一个令人兴奋的领域。通过有助于我们比较陆地，海洋底栖和水生生态系统之间的化学防御理论的能力，这种理解可以产生对这些看似不同的生态系统之间生物相互作用的生态和进化原理的见解。

Chemical defenses ? chemicals used by individuals to reduce or eliminate agents of mortality are diverse, widespread, and important for species interactions. Less studied in planktonic organisms than in terrestrial and marine benthic species, chemical defenses are nonetheless thought to play a role in structuring planktonic communities. They may be particularly important in promoting the formation and persistence of algal blooms. In recent NSF?supported research, we showed that the coccolithophorid Emiliania huxleyi is chemically defended against most tested protist grazer species. At least two aspects of E. huxleyi sulfur chemistry were shown to reduce rates of protist grazing: high DMSP lyase activity (DLA), and exogenous DMSP (dimethylsulfoniopropionate) itself. As both high phytoplankton DLA and dissolved DMSP are present in the sea, we propose that this defense system is important in allowing E. huxleyi blooms to form and persist. Furthermore, as many bloom?forming dinoflagellate and prymnesiophyte species have high intracellular DMSP concentrations and at least some have high DLA, this chemical defense system may be of widespread importance for phytoplankton bloom dynamics. Numerous experiments on this DMSP "defense system" indicated that DMSP is not toxic to protists. Rather, this sublethal defense system might be based on intercellular chemical communication among grazer and prey species. The present proposal constitutes an investigation into the source, mechanism(s) of action, and significance of this defense system.To accomplish this goal, a multi?level investigation will be conducted. Addition of high lyase E. huxleyi cells and defense chemicals to natural water samples and mixed laboratory assemblages will allow testing of community?level defense effects, including possible reductions in microzooplankton grazing, transfer of grazing to other prey types, and allelopathic effects on other phytoplankton species. Population?level studies will reveal whether protist sensitivity to defenses is related to protist taxon, feeding mode, or size. On the individual and molecular levels, a spectrum of possibilities for the mechanism of DMSP?induced feeding inhibition is presented. The effects of chemical cues (DMSP cleavage and oxidation products, algal osmolytes) on protist feeding rates and individual behavior will be studied as a means of testing these possibilities.BROADERIMPACTSThe proposed study will include numerous graduate student and undergraduate participants, including students in Shannon Point Marine Center's Minorities in Marine Science Undergraduate Program. Other outreach activities will include incorporation of concepts, techniques and findings into teaching activities, and preparation of web and print materials aimed at a general audience.INTELLECTUAL MERITDeveloping an increased understanding of sublethal chemical defenses as they involve cell signaling and, ultimately, phytoplankton bloom formation is an exciting area for oceanography, biological sciences, and education. By contributing to our ability to compare chemical defense theory among terrestrial, marine benthic, and planktonic ecosystems, such understanding could yield insights into ecological and evolutionary principles that govern biological interactions across these seemingly diverse ecosystems.