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致死率的化学品种类繁多，分布广泛，对物种相互作用很重要。与陆地和海洋底栖生物相比，对浮游生物的研究较少，尽管如此，化学防御被认为在浮游生物群落的结构中起着作用。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？在支持的研究中，我们证明了球石藻对大多数被测试的原生食草动物物种有化学防御。赫胥黎草硫化学至少在两个方面降低了原生生物的放牧速率：高DMSP裂解酶活性（DLA）和外源DMSP（二甲基磺酰丙酸酯）本身。由于海洋中存在高水平的浮游植物DLA和溶解的DMSP，我们认为这种防御系统对赫胥黎藻华的形成和持续存在很重要。再者，花开多少？形成的鞭毛藻和原膜藻具有高的细胞内DMSP浓度，至少一些具有高的DLA，这种化学防御系统可能对浮游植物的水华动力学具有广泛的重要性。对DMSP“防御系统”的大量实验表明，DMSP对原生生物没有毒性。更确切地说，这种亚致命防御系统可能是基于食草动物和猎物之间的细胞间化学交流。本提案对这一防御制度的来源、作用机制和意义进行了调查。要实现这一目标，多方？将进行水平调查。将高裂解酶赫胥黎细胞和防御化学物质添加到天然水样和混合实验室组合中，可以进行群落？水平防御效应，包括可能减少微型浮游动物的放牧，将放牧转移到其他猎物类型，以及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的分类、摄食方式或大小有关。在个体和分子水平上，DMSP？提出了诱导进食抑制。化学线索（DMSP裂解和氧化产物，藻类渗透物）对原生生物摄食率和个体行为的影响将被研究作为测试这些可能性的一种手段。广泛影响拟议的研究将包括许多研究生和本科生参与者，包括香农角海洋中心海洋科学本科少数民族项目的学生。其他外联活动将包括将概念、技术和发现纳入教学活动，并编制面向一般读者的网络和印刷材料。智力成就：随着对亚致死化学防御的深入了解，因为它们涉及细胞信号，并最终涉及浮游植物的形成，这对海洋学、生物科学和教育来说是一个令人兴奋的领域。通过帮助我们比较陆地、海洋底栖和浮游生态系统之间的化学防御理论，这种理解可以深入了解这些看似不同的生态系统中控制生物相互作用的生态和进化原理。

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.