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

在许多生态系统中，物种之间的互惠互利的相互作用至关重要。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因生态条件的变化而有所不同。这项工作将研究热带美洲发现的树木、蚂蚁和介壳虫之间的三向互惠关系。Cordia alliodora树为阿兹特卡蚂蚁提供了树枝上的生存空间；蚂蚁通过毛虫和甲虫保护树叶不受草食动物的侵害；介壳虫与蚂蚁生活在一起，消耗树上的液体，并喂给蚂蚁富含糖分的排泄物。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的变化。首先，该项目将研究鳞片和蚂蚁与树的相互作用如何依赖于树的生长。新叶子会为树木产生更多的营养，因此蚂蚁的额外保护将是有益的。介壳虫在新叶附近的饲养效果更好吗？这是否会在新叶附近引发更多的蚂蚁防御？其次，该项目将研究这种互惠关系如何依赖于降雨量。在降雨量较大的地点，树木会长得更大，这些地点的树木可能较少依赖蚂蚁来保护自己的叶子。质量较低、降雨量较少的环境中的树木是否会从蚂蚁身上受益更多，尽管蚂蚁会滋生介壳虫？第三，该项目将研究不同种群在蚂蚁防御效果方面的差异。通过比较从墨西哥到阿根廷的蚂蚁种群的遗传结构，将有可能区分出互惠关系在多大程度上源于杂交或当地进化变化。该项目的结果将展示互利互动如何应对生态变化，以及这如何影响他们的进化。该项目将培训美国本科生和研究生，包括来自代表不足群体的个人，并让他们参与国际合作。该项目加强了国际科学基础设施和合作，包括与墨西哥和哥斯达黎加的K-12教师和学生以及普通公众进行接触。该项目使用来自墨西哥和哥斯达黎加的当地居民帮助进行实地工作，来自墨西哥和哥斯达黎加当地大学的学生参与了这项研究。重点树种柳珊瑚是一种具有重要经济意义的重要森林树种，这项工作对管理具有重要的意义。

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.