Eco-evolutionary causes and genomic consequences of synergistic coevolution

进化生物学的一个主要挑战是理解不同生物之间的相互作用如何形成共同进化的过程。虽然这一问题在拮抗相互作用（例如寄生虫与其宿主之间）中得到了很好的理解，但我们对协同进化的认识相当欠发达。具体地说，目前尚不清楚生态相互作用如何决定共同进化种群的进化动态，从而决定相关个体的突变轨迹。这尤其包括协同进化是否以及如何影响相互作用的群体中分子进化和表型多样化的速率的问题。回答这些问题不仅需要了解共同进化过程中发生的突变的顺序和身份，还需要详细了解这些突变对重点相互作用伙伴的生态后果的机制。该项目将利用先前进行的共同进化实验来解决这些问题，在该实验中，大肠杆菌的两种基因型之间进化出了合作互惠主义。将对分离菌株和整个种群进行纵向测序，以揭示协同进化过程中产生的突变的顺序和分布。此外，分离的和基因重建的菌株将受到精心设计的共培养实验，以阐明个体突变如何影响细胞和群体水平上相互作用的基因型的进化动力学。通过这种方式，焦点模型系统的实验可追溯性将有助于确定潜在的生态进化机制，从而有助于理解其他类型的互惠相互作用，在这些相互作用中，类似的分析通常是不可能的。本研究的结果有望显著推进协同共同进化的经验框架的发展，这将在应用和基础研究背景下高度相关。

A major challenge in evolutionary biology is to understand how interactions between different organisms shape the process of coevolution. While this issue is well-understood for antagonistic interactions (e.g. between parasites and their hosts), our knowledge on synergistic coevolution is rather poorly developed. Specifically, it remains unclear how ecological interactions determine the evolutionary dynamics of coevolving populations and thus the mutational trajectories of the individuals involved. This includes in particular the question whether and how synergistic coevolution affects the rates of molecular evolution and phenotypic diversification within interacting consortia. Answering these questions requires not only knowledge on the order and identity of mutations that occurred during coevolution, but also detailed mechanistic insights into the ecological consequences these mutations have for the focal interaction partners. This project will address these issues by taking advantage of a previously performed coevolution experiment, in which a cooperative mutualism evolved between two genotypes of the bacterium Escherichia coli. Both isolated strains and whole populations will be longitudinally sequenced to unravel the order and distribution of mutations that arose during synergistic coevolution. In addition, isolated and genetically reconstructed strains will be subjected to carefully designed coculture experiments to clarify how individual mutations affect the evolutionary dynamics of interacting genotypes on both a cell- and a population-level. In this way, the experimental tractability of the focal model system will help to identify the underlying eco-evolutionary mechanisms and thus helpt to understand other types of mutualistic interactions, in which similar analyses are frequently not possible. The results of this study are expected to significantly advance the development of an empirical framework of synergistic coevolution that will be highly relevant in both applied and fundamental research contexts.