Chemically-mediated competition in the marine plankton

竞争是构建群落的主要力量，包括海洋浮游生物。释放抑制竞争对手的化合物，这一过程被称为化感作用，在浮游植物中被认为是重要的，特别是对那些竞争资源不激烈但成功形成密集繁殖的物种。涉及有毒赤潮鞭毛藻短Karenia的生态相互作用为理解化学介导的竞争和食物网相互作用提供了一个理想的系统。短梭菌的大量繁殖经常发生在墨西哥湾可到达的沿海地区，造成大量鱼类死亡并污染贝类。这些藻华的戏剧性后果为以下问题提供了一个基础：有害藻类是如何战胜共生物种的？毒素动态和其他化学线索起什么作用？浮游生物群落的其他成员是如何受到影响的？它们又是如何应对的？在之前的研究中，研究人员发现，在测试的12种自然共生的浮游植物中，短梭菌对6种具有化感作用，但短梭菌产生的已知神经毒性短梭菌毒素之外的短梭菌化合物通常是负责的。他们还发现，短叶藻的自然、野外繁殖对竞争硅藻骨骸藻具有强烈的化感作用，但骨藻对短叶藻进行报复，降低了其化感作用。此外，在竞争者存在的情况下，水生短毒素被降解。因此，环境背景对于预测哪些具有生态重要性的化学介质被释放到海洋系统以及这些化合物对浮游生物群落的影响可能是至关重要的，这些群落在空间和时间上都是不同的。在本项目中，研究人员将通过野外和实验室实验：1)探索短链镰刀菌化感作用的变异性，包括与弯形镰刀菌的相互作用是否会破坏天然短链镰刀菌花对多个竞争对手的化感作用。2)表征化感作用机制，包括鉴定短链镰刀藻华抑制墨西哥湾竞争者所分泌的化感物质，确定化感物质的作用机制。3)评估化感作用的群落影响，通过测试天然浮游生物群落中浮游植物物种多样性和营养相互作用如何导致化感作用的变化。更广泛的影响：浮游植物大量繁殖会对当地经济造成毁灭性影响，并对人类健康构成威胁。在海洋浮游生物中发现新的化学介导的相互作用可能最终导致预测和缓解策略，以减轻这些水华的有害后果。该项目将以过去的成功为基础，利用化学向我们传授生态过程，并应用生态学的见解来发现具有重要生物功能的独特天然产物。该项目将为一名拉丁裔博士后、一名博士生和几名本科生提供培训。该博士生将扩展我们之前的公共教育培训活动，参加NSF的一个GK-12项目，该项目将佐治亚理工学院的学生安置在亚特兰大地区少数民族学生比例很高的公立高中。这些非裔美国学生将学习科学研究的提问性质，以及与人类对海洋环境影响有关的美国赤潮问题，通过将科学与日常生活联系起来，激发学生对科学的兴趣。

Competition is a major force structuring communities, including the marine plankton. The release of compounds that inhibit competitors, a process known as allelopathy, is hypothesized to be important among phytoplankton, especially for species that compete poorly for resources yet successfully form dense blooms. Ecological interactions involving the toxic red tide dinoflagellate Karenia brevis present an ideal system for understanding chemically-mediated competitive and food web interactions. K. brevis blooms occur frequently in accessible coastal areas of the Gulf of Mexico, causing massive fish kills and contaminating shellfish. The dramatic consequences of these blooms provide a basis for asking: How do harmful algae out-compete co-occurring species? What roles do toxin dynamics and other chemical cues play? How are other members of the plankton community affected and how do they respond? In previous work, the investigators found that K. brevis was allelopathic to 6 out of 12 naturally co-occurring phytoplankton species tested, but that K. brevis compounds other than the known neurotoxic brevetoxins produced by K. brevis were generally responsible. They also found that natural, field blooms of K. brevis were strongly allelopathic to the competing diatom Skeletonema costatum, but that S. costatum retaliates against K. brevis, reducing its allelopathic effects. In addition, waterborne brevetoxins were degraded in the presence of competitors. Thus, environmental context may be critical for predicting what ecologically-important chemical mediators are released into marine systems and the consequences of these compounds on plankton communities, which vary spatially and temporally. In this project, the investigators will use field and lab experiments to: 1) Explore variability in Karenia brevis allelopathy, including whether interactions with S. costatum undermine the allelopathic effects of natural K. brevis blooms on multiple competitors. 2) Characterize mechanisms of allelopathy, including identifying allelopathic compounds exuded by K. brevis blooms that suppress Gulf of Mexico competitors, and determining mechanisms of action of allelopathic compounds. 3) Assess community impacts of allelopathy, by testing how allelopathic effects vary as a result of phytoplankton species diversity and trophic interactions in natural plankton communities. Broader impacts: Phytoplankton blooms can be devastating to local economies and pose human health risks. The discovery of new chemically-mediated interactions in the marine plankton could eventually lead to prediction and mitigation strategies to alleviate the harmful consequences of these blooms. This project will build on past success using chemistry to teach us about ecological processes and applying ecological insights to discover unique natural products with important biological functions. This project will provide training for a Latina postdoc, a PhD student, and several undergraduates. The PhD student will expand on our previous public education training activities, participating in an NSF GK-12 program that places Georgia Tech students in Atlanta-area public high schools with high proportions of minority students. These African-American students will learn about the question-asking nature of scientific research and issues surrounding red tides in the U.S. with connections to human impacts on marine environments, exciting the students about science by connecting it with daily life.