Effect of plant chemical diversity on structuring herbivore populations across different spatial scales

在一个生态群落中，物种间的相互作用构成了当地种群的结构，影响了物种的共存。研究物种相互作用的两种不同但互补的方法是群落遗传学，它认识到物种内的遗传变异可以改变不同物种之间的相互作用；以及元群落生态学，它强调扩散在构建当地群落中的作用。我们利用一个模型Tansy(Tanacum Uggare)植物-蚜虫系统，研究了群落遗传交互作用如何影响集合群落的动态。Tansy的挥发性有机化合物(VOCs)具有很高的种内变异性，这会影响到蚜虫及其天敌的喜好。在这个项目的第一阶段，我们表征了Tansy在单个田间地点的化学类型多样性，并详细研究了寄主植物化学成分的小范围变化如何决定昆虫群落在Tansy植物上的定植模式。我们还研究了Tansy的挥发性(萜烯类)和代谢物(主要是酚类化合物)之间的关系，以及代谢表型(代谢表型)对蚜虫定殖的作用。我们开发了针对蚜虫的微卫星，并在我们田间的小空间范围内发现了植物的挥发性特征与蚜虫基因类型之间的关联。利用实验室装置，我们表征了不同的Tansy化学类型对蚜虫和咀嚼草食动物攻击的反应，以及蚜虫和蚂蚁的寄主选择。总体而言，阶段1提供了植物化学类型对于构建Tansy植物上的昆虫集合群落的重要性的证据。在这里，我们建议将我们的分析扩展到1)更大的空间尺度和2)通过表征根的化学类型来研究地下植物-昆虫的相互作用。在实验室环境中，我们将分析植物根的化学典型成分，以了解植物地上部分和根中的萜类化合物模式之间是否存在代谢和基因关系。然后，我们将使用根食性蚜虫来调查在植物的地下和地上部分取食的蚜虫物种之间是否存在相互作用，以及根和地上部分的化学类型对蚜虫的集合群落结构起到什么作用？利用来自德国及其他地区的样本，我们将研究唐松根和地上部萜类化合物化学类型的地理分布，并分析主要化合物和次要化合物在构建坦西昆虫群落中的作用。通过开发和应用SNP遗传标记，我们还将把植物之间的化学典型差异与优势蚜虫的种群遗传学联系起来。总的来说，该项目将揭示构建田间生态群落的基本机制。

In an ecological community, species interactions structure local populations and influence species coexistence. Two different, yet complementary, approaches to studying species interactions are community genetics, which recognises that within-species genetic variation can alter the interactions between different species; and, metacommunity ecology, which emphasizes the role dispersal plays in structuring local communities. We investigate how community genetic interactions influence metacommunity dynamics, using a model tansy (Tanacetum vulgare) plant – aphid system. Tansy exhibits high intraspecific variation in volatile organic chemicals (VOCs), which can influence the preference of aphids and their natural enemies. In Phase 1 of this project, we characterized the chemotypic diversity of tansy within a single field site and studied in detail how small-scale variation in the chemical composition of the host plant determines colonisation patterns of the insect community on tansy plants. We also studied the relationship between volatile (terpenoids) and metabolomic (mostly phenolic compounds) profiles of tansy, and the role of the metabolic phenotype (‘metabotype’) for aphid colonisation. We developed microsatellites for aphids and found, at the small spatial scale of our field site, an association between the volatile profile of plants and the aphid genotypes. Using laboratory set-ups, we characterized the response of different tansy chemotypes to attack by aphids and a chewing herbivore, and aphid and ant host choice. Overall, Phase 1 provided evidence for the importance of plant chemotypes for structuring the insect metacommunity on tansy plants. Here we propose to extend our analysis to 1) a larger spatial scale and 2) to belowground plant-insect interactions by characterizing the root chemotype. In a laboratory setting, we will analyze the chemotypical composition of the plant roots, to understand if there a metabolic and genotypic relationship between the terpenoid patterns in the aboveground part of the plant and those of the roots. We will then use root-feeding aphids to investigate if there is an interaction between aphid species feeding on the belowground and aboveground parts of the plant, and what roles root and shoot chemotypes play for aphid metacommunity structure? Using samples from across Germany and beyond, we will study the geographical distribution of root and shoot terpenoid chemotypes of tansy and analyze the role of dominant and minor compounds for structuring the insect communities on tansy. By developing and applying SNP genetic markers, we will also link the chemotypical differences between plants to the population genetics of the dominant aphid herbivore.Overall the project will shed light on fundamental mechanisms structuring ecological communities in the field.