Elucidating patterns and processes structuring protist biodiversity across salinity gradients

大多数生物多样性是微生物，包括许多与动物和植物有关的原生生物谱系。原生生物种类繁多，数量众多，对水生生态系统有着巨大的影响，因为它们影响着营养和能量的流动。现在，强大的测序方法使我们能够以前所未有的规模快速表征微生物群落并评估生物多样性。我们将使用这些工具来询问原生生物多样性是如何在不同环境中分布的，以及不同的生态和进化力量（包括选择和扩散）是如何结合起来产生这些生物多样性模式的。从淡水生态系统到海洋生态系统的转变是微生物多样性最强烈的划分，这些环境中生活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，跨越这个屏障通常需要进化创新。然而，生物之间的相互作用也可能是重要的，它们可能通过竞争或优先捕食新来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。这项研究将利用相关研究来复制盐度梯度，并结合操纵性实验，直接测试当盐度变化或增加大型捕食者时，群落组成会发生什么变化。我们还会将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。总之，这些结果将有助于揭示决定哪些原生生物物种生活在不同环境中的机制，以及这些过程在栖息地内部和之间、在地方和区域尺度上以及随着时间的推移是如何不同的。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维持生物多样性的一般生态理论。本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即将产生的影响（如海洋酸化和天气变异性增加）的前沿。因此，了解沿海生态系统中控制微生物真核生物群落组装的过程将能够更好地预测微生物对环境变化的反应，这些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.