Ecological and evolutionary responses to changing environments in a laboratory species assemblage

生态系统面临的环境变化范围很广，从每年的变化到数百万年的变化。此外，人类活动加剧了环境变化的速度和规模。因此，了解生命系统的动态和预测人类活动对这些系统的影响的一项关键任务是了解生态系统如何对环境变化作出反应。可以考虑两种类型的响应。1)生态的。这就导致物种丰度和分布的变化，导致环境变化前后的群落结构不同。2)进化者这需要物种内的基因型变化，导致它们适应环境变化后出现的新条件。尽管对这两种类型的反应做了大量的工作，但它们通常被分开处理。生态系统研究的重点是生态变化，而进化研究的重点是单个物种或相互作用的物种对，如病原体和宿主。然而，大多数生物生活在不同的组合：从这样的小系统的进化动力学的推论可能不适用于现实的设置。该项目将解决物种多样性是否倾向于增加、减少或不影响物种内进化量的基本问题。我们的方法是在实验室中研究进化，使用从山毛榉（Fagus sylvatica）的树洞中分离的细菌物种。这些细菌可以在实验室中以不同数量的物种混合培养，以前曾用于探索多样性与生态系统功能之间的关系。凭借快速的世代时间和非常大的种群规模，它们也进化得足够快，可以研究物种混合物的进化。我们将组装多达24种物种的随机混合物，并将它们暴露于环境变化中，即pH值和资源类型的变化。每个物种的进化反应将使用表型测定进行量化，并在物种丰富度和组成不同的处理之间进行比较。来自相同和不同培养物的分离物之间的竞争实验将测试共同进化相互作用的发生。细菌已被广泛用于测试体外进化假说，但以前的研究没有看到超过一对相互作用的物种的进化。其结果将产生新的概念理解生态系统面临环境变化的生态和进化过程之间的相互作用。

Ecosystems face changing environments over a wide range of time-scales, from yearly changes to those occurring over millions of years. Moreover, the rate and magnitude of environmental change has been intensified by human activities. Therefore, a key task for understanding the dynamics of living systems, and for predicting the impacts of human activity on those systems, is to understand how ecosystems respond to environmental change. Two types of response can be considered. 1) Ecological. This entails changes in species abundances and distribution, leading to a different community structure before and after the environmental change. 2) Evolutionary. This entails genotypic change within species leading to their adaptation to the new conditions present after the environmental change. Despite considerable work on both types of response, typically they have been treated separately. Ecosystem studies have focused on ecological changes, whereas evolutionary studies have focused on single species or pairs of interacting species such as pathogens and hosts. Yet, most organisms live in diverse assemblages: inferences on evolutionary dynamics from such small systems may not apply in realistic settings. This project will address the fundamental question of whether species diversity tends to increase, decrease or not affect the amount of evolution within species. Our approach is to study evolution in the laboratory, using species of bacteria isolated from tree-holes of beech (Fagus sylvatica). These bacteria can be cultured in mixtures of different numbers of species in the lab, and have been used previously to explore the relationship between diversity and ecosystem function. By virtue of rapid generation times and very large population sizes, they also evolve fast enough to study evolution in species mixtures. We will assemble random mixtures of up to 24 species and expose them to environmental change, in terms of a shift in pH and resource type in turn. The evolutionary response of each species will be quantified using phenotypic assays and compared among treatments that differ in species richness and composition. Competition experiments between isolates from the same and different cultures will test for the occurrence of coevolutionary interactions. Bacteria have been widely used to test evolutionary hypotheses in vitro, but no previous studies have looked evolution in more than a pair of interacting species. The results will generate new conceptual understanding of the interaction between ecological and evolutionary processes in ecosystems facing environmental change.