Elucidating patterns and processes structuring protist biodiversity across salinity gradients

大多数生物的多样性是微生物，包括与动植物相关的许多原生动物的谱系。原生生物种类繁多，数量惊人，并对水生生态系统产生巨大影响，因为它们影响营养物质和能量的流动。现在，强大的测序方法使我们能够快速确定微生物群落的特征，并以前所未有的规模评估生物多样性。我们将使用这些工具来询问原生生物多样性是如何在环境中分布的，以及不同的生态和进化力量，包括选择和扩散，如何结合在一起产生这些生物多样性模式。从淡水生态系统向海洋生态系统的过渡是微生物多样性中最强烈的分歧，这些环境中栖息着非常不同类型的生物。盐度和pH等环境因素被认为是造成这种差异的主要原因，因为它们共同构成了一个巨大的生理屏障，跨越它通常需要进化创新。然而，生物体之间的相互作用也有可能是重要的，它们可能会通过竞争或优先捕食新到达的微生物来加强环境边界。我们将收集环境参数和整个微生物群落(原生生物和细菌)的数据，首次从整个群落的角度来解决这个问题。这项研究将使用重复盐度梯度的相关研究，并结合操控实验，直接测试盐度变化或添加大型捕食者时群落组成的变化。我们还将把整个群落移植到不同条件下的新环境中，看看哪些微生物能存活下来。总而言之，这些结果将有助于揭示决定哪些原生动物物种生活在不同环境中的机制，以及这些过程在生境内部和栖息地之间、跨地区和区域尺度以及随着时间的推移是如何变化的。在此过程中，我们还将评估扩散在构建微生物群落中的作用，并测试生物地理学和生物多样性维护的一般生态学理论。这项研究在以盐度梯度为特征的沿海环境和河口进行。沿海生态系统和河口提供了许多有益于人类的生态系统服务，但这些重要的生态系统受到包括农业径流和污水排放在内的人类活动的威胁。沿海生态系统也处于气候变化迫在眉睫的影响的前线，例如海洋酸化和天气变化性增加。因此，了解管理沿海生态系统中微生物真核生物群落组装的过程将使我们能够更好地预测微生物对环境变化的反应，这些环境变化是我们这个时代最紧迫的问题之一，以及这些系统一般是如何工作的。

Most organismal diversity is microbial, including the numerous lineages of protists that are related to animals and plants. Protists are incredibly diverse, abundant, and have huge impacts on aquatic ecosystems because they influence the flow of nutrients and energy. Powerful sequencing approaches now enable us to rapidly characterize microbial communities and assess biodiversity on an unprecedented scale. We will use these tools to ask how protist diversity is distributed across environments and how different ecological and evolutionary forces, including selection and dispersal, combine to produce these biodiversity patterns. The transition from freshwater to marine ecosystems is of the strongest divisions in microbial diversity, with very different types of organisms inhabiting these environments. Environmental factors such as salinity and pH are thought to be largely responsible for this difference because together they constitute a large physiological barrier and crossing it usually requires evolutionary innovation. However, it is also possible that interactions among organisms are important, and they may reinforce the environmental boundary by out-competing or preferentially preying on newly arrived microbes. We will collect data on environmental parameters and the whole microbial community (protists and bacteria) to address this question from the perspective of the whole community for the first time. This research will use correlative studies along replicate salinity gradients combined with manipulative experiments that directly test what happens to community composition when salinity changes or a large predator is added, for example. We will also transplant entire communities to new environments under different conditions to see which microbes survive. Together these results will help uncover the mechanisms that determine which species of protists live in different environments, and how these processes differ within and between habitats, across local and regional scales, and over time. Along the way, we will also assess the role of dispersal plays in structuring microbial communities and test general ecological theories of biogeography and the maintenance of biodiversity. This research takes place in coastal environments and estuaries that are characterized by salinity gradients. Coastal ecosystems and estuaries deliver numerous ecosystem services that benefit humans, but these important ecosystems are threatened by human activities including agricultural runoff and sewage effluent. Coastal ecosystems are also on the frontlines of impending effects of climate change such as ocean acidification and increased variability in weather. Thus, understanding the processes that govern microbial eukaryotic community assembly in coastal ecosystems will enable better predictions of the response of microbial organisms to environmental changes that are among the most pressing concerns of our time and how these systems work in general.