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

引进的物种可以通过取代本地物种和改变环境条件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）知之甚少。根瘤菌是一种有益的细菌，栖息在豆科植物的根组织中，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。豆科植物分散到缺乏这些细菌的栖息地通常无法持续存在，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会改变互惠互动的本质。研究人员将研究两种植物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解决，但这是第一个利用地下植物共生关系的系统。该项目将促进科学多样性，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。还将开发一个关于根瘤菌-豆科植物在社区土壤中的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发展项目和仙童挑战项目（一个每年在迈阿密惠及10万多名儿童的环境教育项目）分发给在校儿童。为了了解在物种入侵过程中互惠互利是否变得不那么有利，本项目将测试来自两种紫花苜蓿的本地和入侵范围的豆科植物和根瘤菌基因型的伴侣宽度和互惠互利之间的假设权衡。紫花苜蓿属包括紫花苜蓿。这两个物种都原产于欧洲，并在美国入侵。研究人员将：(1)利用宿主的高标记密度基因分型和共生体的全基因组测序，比较本地和入侵宿主范围互惠主义者的遗传多样性；(2)利用交叉接种试验，评估本地和入侵范围互惠主义者之间互惠特性的差异，以检验入侵范围互惠主义者专业化程度降低、伴侣选择和互惠依赖的假设。3)在不同寄主密度和多样性的条件下，通过模拟土壤中生态系统中共生生物的入侵，测试入侵对共生生物基因组动态和共生关系的影响；4)利用转录组学方法确定共生特化的分子基础，以确定寄主-共生途径。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在拥有广泛的伴侣范围和为伴侣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.