International Research Fellowship Program: The Impact of Environmental Heterogeneity on Coevolution in a Tritrophic Plant-bacteria-phage Interaction

[0754399]科斯凯拉国际研究奖学金计划使美国科学家和工程师能够到国外进行9至24个月的研究。该计划的奖励为联合研究提供了机会，并利用独特或互补的设施、专业知识和国外的实验条件。该奖项将支持Britt Koskella博士与英国牛津大学的Angus buckle博士（13个月）和加州大学圣克鲁斯分校的John Thompson博士（11个月）进行为期24个月的研究。越来越明显的是，宿主及其寄生虫之间的共同进化发生在相对较短的时间内，并受到相互作用发生的环境的强烈影响。虽然环境条件影响物种的相互作用是显而易见的，但基因流在异质景观中的共同进化过程究竟是如何形成的还有待解决。该项目采用了一种新颖的方法来进行实验共同进化分析，通过扩大成对共同进化的研究，包括在复杂景观中与第三种物种的相互作用。PI和宿主将研究植物种群、植物致病菌丁香假单胞菌及其相关噬菌体之间的营养相互作用。该系统是在微生物水平上确定共同进化事件的规模和幅度的理想系统，因为噬菌体的传播影响了细菌的运动和种群大小，从而影响了细菌对宿主植物的影响。此外，由于每个物种都直接受到周围环境条件的影响，并且本身也作为其他两个相互作用物种的变化环境，他们将能够使用三向相互作用来检查景观异质性对共同进化过程的影响。通过精心控制的选择实验和自然种群调查的新组合，他们将系统地检查共同进化的地理马赛克理论的每个组成部分，首先通过量化细菌运动的程度，已知影响细菌毒力，以及相应的噬菌体生活史特征在宿主植物物种和种群中变化。通过建立一系列操控植物寄主环境的丁香假单胞菌与噬菌体的人工协同进化实验，评价了相互选择的变异和基因流的相对作用。为了补充这一实验性协同进化工作，研究人员还对来自不同地理区域和寄主植物物种的自然种群中噬菌体的患病率、特异性和局部适应性进行了调查。在物种相互作用过程中，地理变异对相互选择的相对重要性的实证研究很少；因此，拟议的工作将极大地扩展我们对不断变化的环境条件如何影响宿主-寄生虫共同进化的理解。本研究还将为噬菌体治疗在植物病原菌控制中的新应用提供基础。此外，该项目对病原体在复杂景观中的移动的关注将在面对大规模、人为介导的作物病原体传播时提供特别有用的信息。

0754399KoskellaThe International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a twenty-four month research fellowship by Dr. Britt Koskella to work with Dr. Angus Buckling at the University of Oxford in the UK (thirteen months) and with Dr. John Thompson at the University of California, Santa Cruz (eleven months).It is becoming abundantly evident that coevolution between hosts and their parasites occurs in relatively short time periods and is strongly influenced by the environment in which the interaction is occurring. Although it is clear that environmental conditions influence species interactions, exactly how the process of coevolution is shaped by gene flow across a heterogeneous landscape is yet to be resolved. This project takes a novel approach to experimental coevolutionary analysis by scaling up studies of pairwise coevolution to include interactions with a third species across a complex landscape. The PI and hosts will examine a tritrophic interaction between plant populations, the plant pathogenic bacteria Pseudomonas syringae, and its associated bacteriophages. This system is ideal for establishing the scale and magnitude of coevolutionary events at a microbial level in that the spread of bacteriophage influences both the movement and population size of bacteria, and thus the impact of bacteria on the host plant. Furthermore, since each species is directly influenced by the surrounding environmental conditions and is itself acting as a changing environment for the other two interacting species they will be able to use the three-way interaction to examine the implications of landscape heterogeneity for the coevolutionary process. Through a novel combination of carefully controlled selection experiments and surveys of natural populations they will systematically examine each component of the Geographic Mosaic Theory of Coevolution, first by quantifying the extent to which bacterial motility, known to affect bacterial virulence, and corresponding phage life-history traits vary among host plant species and populations. By setting up a series of artificial coevolution experiments between P. syringae and phage in which the plant host environment is manipulated, the variation in reciprocal selection and the relative role of gene flow is being evaluated. To complement this experimental coevolution work, a survey of phage prevalence, specificity, and local adaptation across natural populations from different geographic regions and host plant species is also being performed. Few studies have empirically explored the relative importance of geographic variation for reciprocal selection during species interactions; the proposed work will therefore greatly expand our understanding of how changing environmental conditions affect host-parasite coevolution. This research will additionally provide the basis for a novel use of phage therapy in controlling pathogenic plant bacteria. Furthermore, the project's focus on pathogen movement across complex landscapes will be particularly informative in the face of large-scale, human-mediated dispersal of crop pathogens.