Evolutionary ecology of a multi-species mutualism at a regional scale

在许多生态系统中，物种之间的相互作用是至关重要的，在这种相互作用中，每个物种都使其他物种受益。涉及两个以上互惠伙伴的互动很常见，但很少被研究。互惠伙伴之间的服务交换随着生态条件的变化而变化。这项工作将研究在热带美洲发现的树木，蚂蚁和蚧虫之间的三方互惠关系。阿兹特克蚂蚁生活在科迪亚的树枝上；蚂蚁保护树叶免受毛虫和甲虫的食草；蚧虫与蚂蚁生活在一起，从树上吸取液体，并将富含糖分的排泄物喂给蚂蚁。该项目将调查这些互惠伙伴之间相互作用的三种变化：随着树木的生长，对栖息地质量的生态差异的反应，以及长期进化时间尺度。首先，该项目将研究鳞片和蚂蚁与树木的相互作用如何取决于树木的生长。新叶为树提供更多的营养，所以蚂蚁的额外保护将是有益的。介壳虫在新叶附近吃得更好吗？这是否会引起蚂蚁在新叶附近更多的防御？其次，该项目将研究这种共生关系如何取决于降雨量。在降雨量高的地方，树木会长得更大，这些地方的树木可能不太依赖蚂蚁来保护它们的叶子。在低质量的环境中，降雨量少，树木是否从蚂蚁那里受益更多，尽管蚂蚁倾向于蚧虫？第三，该项目将检查蚁群防御效率的差异。通过比较墨西哥和阿根廷蚂蚁种群的遗传结构，将有可能区分出共生关系在多大程度上源于杂交或局部进化变化。该项目的结果将展示互惠互动如何应对生态变化，以及生态变化如何影响它们的进化。该项目将培训美国本科生和研究生，包括来自代表性不足群体的个人，并使他们参与国际合作。该项目加强了国际科学基础设施和合作，包括向墨西哥和哥斯达黎加的K-12教师和学生以及公众进行宣传。该项目利用墨西哥和哥斯达黎加的当地居民帮助进行实地工作，墨西哥和哥斯达黎加当地大学的学生参与研究。焦点树种阿廖多拉（Cordia alliodora）是一种具有重要经济价值的重要林木，对管理具有重要意义。

Mutualist interactions between species, in which each species benefits the other, are vitally important in many ecosystems. Interactions involving more than two mutualist partners are common, but rarely studied. The exchange of services between mutualist partners varies in response to changing ecological conditions. This work will examine a three-way mutualism among trees, ants, and scale insects found in the tropical Americas. Cordia alliodora trees provide living space for Azteca ants in their branches; the ants defend the tree's leaves from herbivory by caterpillars and beetles; and scale insects live with the ants, consume fluids from the tree and feed the ants their sugar-rich excretion. The project will investigate three kinds of changes in the interactions among these mutualist partners: as the tree grows, in response to ecological differences in the quality of the habitat, and on the long-term evolutionary timescale. First, the project will examine how the interaction of scales and ants with the tree depends on the tree growth. New leaves produce more nutrients for the tree, so additional protection by ants would be beneficial. Are scale insects better fed near new leaves, and does this induce more ant defense near new leaves? Second, the project will examine how the mutualism depends on the amount of rainfall. Trees grow larger at sites with higher rainfall, and trees at these sites may be less dependent on ants to defend their leaves. Do trees in lower quality environments, with less rainfall, benefit more from the ants, despite the scale insects that the ants tend? Third, the project will examine differences among populations in the effectiveness of ant defense. By comparing the genetic structure of ant populations from Mexico to Argentina, it will be possible to distinguish how much the mutualism arises from interbreeding or from local evolutionary change. The results of the project will show how mutualistic interactions can respond to ecological change and how this influences their evolution.This project will train US undergraduates, and graduate students, including individuals from under-represented groups, and involve them in international collaboration. The project strengthens international scientific infrastructure and collaboration and includes outreach to K-12 teachers and students, as well as the general public, in Mexico and Costa Rica. The project uses local residents from Mexico and Costa Rica to help with field work and students from local Mexican and Costa Rican universities participate in the research. The focal tree species, Cordia alliodora, is an important forest tree of significant economic importance and the work has important implications for management.