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

引入的物种会取代本地物种并改变环境条件，从而对生态系统造成严重破坏。虽然对入侵植物和动物的特性了解很多，但对伴随引入物种的有益微生物（微生物）的了解要少得多。根瘤菌是有益的细菌，栖息在豆科植物根组织中，在那里它们将大气中的氮转化为植物可利用的形式。豆科植物通过光合作用为这些微生物提供糖。分散到缺乏这些细菌的栖息地的豆类通常无法持续存在，但是细菌也可以通过土壤或空气传播。本研究的目的是检验入侵是否改变了互惠互动的性质。 研究人员将研究两种植物物种及其有益微生物在自然和实验阶段入侵中的专业化和合作进化。虽然这个问题已经在地上系统中得到了解决，但这是第一个利用地下植物互利共生的系统。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滨江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的凯洛格生物站生物能源可持续性计划和费尔柴尔德挑战赛分发给学童，费尔柴尔德挑战赛是一个环境教育计划，每年在迈阿密有超过10万名儿童参加。该项目将测试两个苜蓿属物种的来自本地和入侵范围的豆科植物和根瘤菌基因型之间的伙伴广度和互利共生效益之间的假设权衡。苜蓿属是包括紫花苜蓿在内的一个属。这两个物种都原产于欧洲，在美国具有入侵性。研究人员将1）使用高标记密度的宿主基因分型和共生体的全基因组测序，比较本地与入侵宿主范围互利主义者的遗传多样性，2）评估本地和入侵范围之间互利主义性质的差异，以测试使用交叉接种试验的入侵范围互利主义者的专业化程度降低，伴侣选择和互利主义依赖的假设，3）通过模拟不同宿主密度和多样性条件下的共生体入侵，测试入侵对共生体基因组动态和互惠的影响; 4）利用转录组学方法确定宿主-共生体途径，确定互惠专化的分子基础。这项研究将揭示一个长期存在的问题，即有益微生物是否面临着广泛的合作伙伴范围和为合作伙伴提供高度利益之间的权衡。

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.