Breaking boundaries: quantifying the influence of demography and seascape in driving adaptive variation in the ubiquitous protist Oxyrrhis marina.

从群落到物种和种群再到基因，所有层级的生物多样性对生态系统健康至关重要。因此，至关重要的是提供一个强大的框架，以了解促进或限制适应性差异和对新环境的潜在反应的机制。第一步是评估物种内的这些过程。我们将通过采用跨学科的方法来做到这一点，这种方法提供了一种独特的检查，即驱动适应性差异的景观和关键人口参数之间的相互作用。决定适应性分化的两个关键过程：基因流动(分散个体的基因运动)和有效的种群规模(即只有那些为下一代贡献基因的个体)。高基因流动是一种凝聚的进化力量，限制了遗传分化，从而限制了生态专门化和最终物种形成的机会。相反，许多物种是由于低基因流动的结果而局部适应的，有时是由于地理距离很大，但往往是因为种群分布在具有特定障碍的异质景观中，而不是距离本身限制了行动。小的有效种群规模也促进了遗传分化，但这个过程可能是非适应性的，因为在这种情况下，随机过程而不是自然选择形成了基因组结构。我们的研究旨在解决两个广泛的问题：1)种群之间的适应性差异有多大？2)人口统计参数、基因流动和有效种群规模如何促进或限制差异？很容易想象，在斑驳的陆地和淡水系统中，人口参数(分散的、有效的人口数量)与景观基质密切相关。然而，对于海洋远洋环境来说，这就不那么明显了，因为传统上人们认为海洋远洋环境是“开放系统”，几乎没有阻碍基因流动的障碍。这一观点现在受到了挑战，特别是对海洋景观(海景)的新兴研究，这些研究认识到海洋特征限制了后生动物的扩散。相比之下，小型浮游生物，如原生生物(单细胞真核生物)，被推测为无处不在的分散体，因为它们很容易被风和水流输送。推论是，与后生动物的描述相反，原生动物种群的适应差异将是有限的；鉴于原生动物表现出巨大的分类学和功能多样性，这呈现出明显的悖论，这意味着要么基因流动有限，要么强大的环境压力(如温度、盐度)驱动适应。这个问题需要解决，因为原生生物在生态上很重要，了解生态专业化的程度对于预测对环境变化的反应至关重要。具体地说，我们通过将实验和分子技术应用于原生生物模型来解决四个问题：1)原生生物种群边界在哪里？2)基因流和有效种群规模的值是什么？3)种群如何对海洋系统中的关键环境变量做出反应：温度和盐度？4)后生动物和原生动物受海景的影响相似吗？必须同时解决这些问题，才能真正了解基因流动、有效种群规模和海景之间的相互作用。我们的答案有望为浮游生物的扩散和适应提供基本的见解，潜在地指导海洋资源的管理，因为浮游生物可以对生态系统健康产生有益(例如影响食物网碳通量)和有害(例如有毒水华)的影响。这些数据还对更广泛的问题有重大影响，通过确定1)尽管或没有高基因流动，适应性分化发生的程度，以及2)原生动物和后生动物进化过程之间是否存在根本差异。

Biodiversity at all hierarchical levels, from communities to species and populations to genes, is critical for ecosystem health. It is essential, therefore, to provide a robust framework to understand mechanisms that promote or constrain adaptive divergence and potential response to new environments. A first step is to assess these processes within species. We will do this by employing an interdisciplinary approach that provides a unique examination of the interplay between landscape and key demographic parameters that drive adaptive divergence. Two key processes determine adaptive divergence: gene flow (gene movement by dispersing individuals) and effective population size (ie only those individuals that contribute genes to the next generation). High gene flow is a cohesive evolutionary force that limits genetic differentiation, thus restricting opportunity for ecological specialisation and ultimately speciation. Conversely, many species are locally adapted as a result of low gene flow, sometimes due to large geographic distances, but often because populations are distributed throughout heterogeneous landscapes with specific barriers, not distance per se, limiting movement. Genetic divergence is promoted also by small effective population size, but this process may be non-adaptive as under such circumstances random processes rather than natural selection shapes genome structure. Our study is designed specifically to resolve two broad questions: 1) how much adaptive divergence occurs between populations? 2) how do the demographic parameters, gene flow and effective population size, promote or constrain divergence? It is easy to visualise that in patchy terrestrial and freshwater systems demographic parameters (dispersal, effective population size), are intimately linked with the landscape matrix. However, this is less obvious for marine pelagic environments, which are traditionally viewed as 'open systems' with few barriers to gene flow. This view is now challenged, particularly by emerging research into the marine landscape (seascape) that recognises oceanographic features limit dispersal of metazoans. In contrast, small planktonic organisms, such as protists (single-celled eukaryotes), are speculated to be ubiquitously dispersed as they can be readily transported by wind and water currents. The corollary is that adaptive divergence of protist populations will be limited, in contrast to that described for metazoans; this presents an apparent paradox given the large taxonomic and functional diversity exhibited by protists, implying that either gene flow is limited or strong environmental pressures (eg temperature, salinity) drive adaptation. This issue requires addressing as protists are ecologically important and understanding the extent of ecological specialisation is critical to predict response to environment change. Specifically, we address this issue by applying experimental and molecular techniques to a protist model to resolve four questions: 1) where are protist population boundaries? 2) what are the values of gene flow and effective population sizes? 3) how do populations respond to key environmental variables in the marine system: temperature & salinity? and 4) are metazoans and protists similarly influenced by seascape? It is essential to simultaneously address these questions to truly understand the interplay between gene flow, effective population size and seascape. Our answers promise to offer fundamental insights into dispersal and adaptation of plankton, potentially guiding management of marine resources as plankton can have beneficial (eg influencing food web carbon flux) and harmful (eg toxic blooms) influences on ecosystem health. These data also have a major bearing on wider issues, by determining 1) the extent to which adaptive divergence occurs despite, or in the absence of, high gene flow and 2) whether there are fundamental differences between protist and metazoan evolutionary processes.