Dynamics of Protistan Grazers: Diversity, Abundance and Prey Relations

水生生态系统中一些最重要的初级生产者和消费者是原生生物或单细胞真核生物。原生生物的捕食是造成细菌和浮游植物死亡的重要原因。食草原生生物反过来又成为浮游动物（桡足类）的猎物，通过排泄氮和磷化合物，它们在释放再生营养物质中起着重要作用。尽管对原生动物放牧进行了数十年的研究，但在它们的丰度、分布、季节性、猎物选择性和共生模式方面仍然存在知识空白。该项目的结果将促进对原地放牧群落的理解，以及它们如何对环境条件和猎物群落做出反应。这将是为数不多的不受人工捕食和围捕影响的食草动物研究之一，并将获得有关现存生物和特定食草动物种群分布模式的形态和遗传信息。一名研究生将完成她的论文工作，作为该项目的一部分，并选择本科生参与研究。在与Zephyr教育基金会的海洋科学素养和教育项目的合作中，教师将开发一个基于微生物食物网的教育单元，为6-8年级的学生量身定制。本项目研究了一群原生食草动物的持久性是否由其摄食策略决定（具有专业摄食策略的食草动物比通才摄食策略的食草动物更短暂），以及表现出通才摄食策略的某些形态是否具有潜在的基因型多样性，从而映射到专业摄食策略。它建立在一个持续的时间序列（自2006年以来每小时的分辨率）上，由玛莎葡萄园海岸天文台的Imaging FlowCytobot对浮游植物群落进行了自动化、高分辨率的测量。这些测量结果表明，除了夏季的微型和小型纳米浮游生物向秋季和冬季较大的微型浮游生物转变之外，某些物种（尤其是硅藻）表现出独特的周期性模式。该仪器还将进行改进，以便对原地食草动物群落进行自动测量。选定的食草动物类群（根据图像时间序列选择）和浮游植物猎物之间的联系将通过对单个细胞（与其摄入的猎物）的遗传分析来提供。这些细胞将通过使用最近开发的细胞分选器获得，该分选器还捕获每个被分选细胞的图像。除了提供捕食者/猎物之间的联系外，遗传信息将使研究人员能够确定一个食草动物的形态是否代表多个物种。第三种方法，对整个水样进行高通量测序和定量PCR分析，将用于研究那些形态不能可靠地映射到基因型的物种的丰度模式。

Some of the most important primary producers and consumers in aquatic ecosystems are protists, or single-celled eukaryotes. It is well established that protistan predation can be a significant source of mortality for bacteria and phytoplankton. Grazing protists in turn serve as prey for zooplankton (copepods), and through the excretion of nitrogen and phosphorus compounds, they play a major role in the release of regenerated nutrients. Despite decades of studies on protistan grazing, knowledge gaps still exist with respect to their abundance, distribution, seasonality, prey selectivity, and co-occurrence patterns. The results from this project will advance the understanding of grazing communities in situ and how they respond to environmental conditions and prey communities. This will be one of very few studies of grazers that is unbiased by artificial prey and containment, and will yield both morphologic and genetic information about the organisms present and the distribution patterns of particular grazer populations. A graduate student will be performing her thesis work as part of this project, and selected undergraduates will be involved in the research. In partnership with the Zephyr Education Foundation's marine science literacy and education program, teachers will develop an educational unit based on the microbial food web that is tailored to grade levels 6-8. This project examines whether the persistence of a group of protistan grazers is determined by its feeding strategy (grazers with specialist feeding strategies are more ephemeral than generalists), and whether certain morphotypes exhibiting generalist feeding strategies have underlying genotypic diversity that maps to specialist feeding strategies. It builds upon an ongoing time series (with hourly resolution since 2006) of automated, high-resolution, measurements of the phytoplankton community by the Imaging FlowCytobot at the Martha's Vineyard Coastal Observatory. These measurements have led to the observation that, in addition to shifts from pico- and small nanoplankton during the summer to larger microplankton in the fall and winter, particular species (especially among the diatoms) exhibit distinct and recurring seasonal patterns. The instrument will be modified to also conduct automated measurements of grazer communities in situ. Links between selected grazer taxa (chosen based on the image time series) and phytoplankton prey will be provided through genetic analyses of individual cells (with their ingested prey). These cells will be obtained by use of a recently developed cell sorter that also captures an image of each sorted cell. In addition to providing predator/prey links, the genetic information will allow the investigators to determine whether a grazer morphotype represents multiple species. A third approach, high throughput sequencing and quantitative PCR analysis of whole water samples, will be applied to investigate abundance patterns of species whose morphology does not reliably map to genotype.