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

生态系统面临着广泛的时间尺度上的环境变化，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幅度。因此，要了解生命系统的动态，并预测人类活动对这些系统的影响，一项关键任务是了解生态系统如何响应环境变化。可以考虑两种类型的响应。1)生态化。这导致了物种丰度和分布的变化，导致了环境变化前后不同的群落结构。2)进化型。这需要物种内的基因类型变化，导致它们适应环境变化后出现的新条件。尽管在这两种类型的反应上做了大量的工作，但通常情况下，它们都被分开治疗。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，大多数生物体生活在不同的组合中：从这样的小系统对进化动力学的推断可能不适用于现实环境。这个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根本问题。我们的方法是在实验室里利用从山毛榉树洞中分离出的各种细菌来研究进化。这些细菌可以在实验室中不同数量的物种的混合物中培养，以前曾被用来探索多样性和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，它们的进化速度也足够快，足以研究物种混合的进化。我们将组装多达24个物种的随机混合物，并根据pH值和资源类型的变化依次将它们暴露在环境变化中。每个物种的进化反应将使用表型分析进行量化，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菌株之间的竞争实验将测试共同进化相互作用的发生。细菌已被广泛用于在体外测试进化假说，但此前没有一项研究着眼于超过一对相互作用的物种的进化。这些结果将对面临环境变化的生态系统中的生态和进化过程之间的相互作用产生新的概念性理解。

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.