Collaborative Research: Ecological and Evolutionary Forces Reshaping Mutualism During Species Introductions

引入的物种可以通过取代原住民和改变环境条件来对生态系统造成严重破坏。虽然人们对入侵动植物的特性知道得很多，但对伴随着引入物种的有益微生物(微生物)的了解要少得多。根瘤菌是一种有益的细菌，它们生活在豆科植物的根组织中，在那里它们将大气中的氮转化为植物可利用的形式。豆科植物为这些微生物提供光合作用产生的糖。散布到缺乏这些细菌的栖息地的豆类通常无法持久，然而细菌也可以通过土壤或空气传播。这项研究的目的是检验入侵是否改变了互利互动的性质。研究人员将研究两种植物及其有益微生物在自然入侵和实验入侵中的专门化和合作进化。虽然这个问题已经在地上系统中得到了解决，但这是第一次利用地下植物的互惠共生。该项目将促进科学的多样性，提供植物-微生物相互作用生物学方面的研究、培训和教育，并为控制入侵植物的努力提供信息。来自佛罗里达国际大学的不同本科生将参加加州大学河滨分校和密歇根州立大学的暑期研究。还将开发一个关于附近土壤中根瘤菌-豆类相互作用的教育模块，通过密歇根州立大学凯洛格生物站生物能源可持续发展计划和费尔柴尔德挑战计划分发给学童，费尔柴尔德挑战是一个环境教育计划，每年在迈阿密有超过10万名儿童。为了了解互惠互利在物种入侵过程中是否变得不那么有益，该项目将测试两种紫花苜蓿物种在原生和入侵范围内的豆类和根瘤菌基因型之间的合作伙伴广度和互惠互利之间的假设权衡。紫花苜蓿是包括紫花苜蓿在内的一个属。这两个物种都原产于欧洲，入侵美国。研究人员将1)比较原生和入侵寄主范围互惠共生体的遗传多样性，使用宿主的高标记密度基因分型和共生体的全基因组测序，2)评估原生和入侵范围互惠共生体之间的互惠特性的差异，通过交叉接种试验测试入侵互惠共生体的专门化程度降低、伙伴选择和互惠依赖的假设，3)在对比寄主密度和多样性的情况下，测试入侵对共生体基因组动力学和互惠共生的影响，以及4)使用转录断层方法来命名寄主-共生致病途径，以确定互惠专化的分子基础。这项研究将阐明一个长期存在的问题，即有益微生物是否面临着在拥有广泛的伴侣范围和为伴侣提供高度好处之间的权衡。

Introduced species can wreak havoc on ecosystems by displacing natives and by altering environmental conditions. While much is known about the properties of invasive plants and animals, much less is known about the beneficial microbes (microscopic organisms) that accompany introduced species. Rhizobia are beneficial bacteria that inhabit leguminous plant root tissue where they convert nitrogen from the atmosphere to a plant-available form. Leguminous plants provide these microbes with sugars from photosynthesis. Legumes that disperse to habitats that lack these bacteria are typically unable to persist, however the bacteria can also spread through the soil or air. The aim of this research is to examine whether invasions change the nature of a mutualistic interaction. The investigators will study specialization and the evolution of cooperation in both natural and experimentally staged invasions for two plant species and their beneficial microbes. While this question has been addressed in aboveground systems, this is one of the first to utilize a belowground plant mutualism. This project will promote diversity in the sciences, provide research training and education in the biology of plant-microbe interactions, and inform efforts to control invasive plants. Diverse undergraduate students from Florida International University will participate in summer research at University of California at Riverside and Michigan State University. An educational module will also be developed on rhizobium-legume interactions in neighborhood soils, to be distributed to school children via MSU's Kellogg Biological Station Bioenergy Sustainability Program and the Fairchild Challenge, an environmental education program that reaches over 100,000 children a year in Miami.To understand whether mutualisms become less beneficial in the process of species invasions, this project will test the hypothesized trade-off between partner breadth and mutualism benefit across legume and rhizobium genotypes from the native and invasive range for two Medicago species. Medicago is the genus that includes alfalfa. Both species are native to Europe and invasive in the US. The researchers will 1) compare genetic diversity in native vs. invaded host range mutualists, using high marker density genotyping for hosts and whole-genome sequencing for symbionts, 2) assess divergence in mutualism properties between the native and invaded range to test hypotheses of reduced specialization, partner choice and mutualism dependence in invaded range mutualists using cross-inoculation trials, 3) test the impact of invasion on symbiont genome dynamics and mutualisms by simulated symbiont invasions in soil mesocosms under contrasting host density and diversity, and 4) identify the molecular underpinnings of mutualism specialization using a transcriptomic approach to nominate host-symbiont pathways. This research will shed light on the long-standing question of whether beneficial microbes face a trade-off between having a broad partner range and providing a high degree of benefit to a partner.