Data from: The many dimensions of diet breadth: phytochemical, genetic, behavioral, and physiological perspectives on the interaction between a native herbivore and an exotic host

From the perspective of an herbivorous insect, conspecific host plants are not identical, and intraspecific variation in host nutritional quality or defensive capacity might mediate spatially variable outcomes in plant-insect interactions. Here we explore this possibility in the context of an ongoing host breadth expansion of a native butterfly (the Melissa blue, Lycaeides melissa) onto an exotic host plant (alfalfa, Medicago sativa). We examine variation among seven alfalfa populations that differed in terms of colonization by L. melissa; specifically, we examined variation in phytochemistry, foliar protein, and plant population genetic structure, as well as responses of caterpillars and adult butterflies to foliage from the same populations. Regional patterns of alfalfa colonization by L. melissa were well predicted by phytochemical variation, and colonized patches of alfalfa showed a similar level of inter-individual phytochemical diversity. However, phytochemical variation was a poor predictor of larval performance, despite the fact that survival and weight gain differed dramatically among caterpillars reared on plants from different alfalfa populations. Moreover, we observed a mismatch between alfalfa supporting the best larval performance and alfalfa favored by ovipositing females. Thus, the axes of plant variation that mediate interactions with L. melissa depend upon herbivore life history stage, which raises important issues for our understanding of adaptation to novel resources by an organism with a complex life history.从植食性昆虫（herbivorous insect）的视角出发，同种寄主植物（conspecific host plants）并非全然同质，寄主营养质量或防御能力的种内变异（intraspecific variation）可能介导植物-昆虫互作（plant-insect interactions）中存在空间异质性的交互结果。本研究围绕本土蝴蝶梅利莎蓝蝶（Melissa blue, Lycaeides melissa）正向外来寄主植物（exotic host plant）苜蓿（Medicago sativa, alfalfa）扩张寄主范围（host breadth expansion）这一正在进行的过程，探讨了上述可能性。我们选取了7个被L. melissa定殖程度存在差异的苜蓿种群开展研究，具体分析了其植物化学组成（phytochemistry）、叶蛋白含量（foliar protein）以及种群遗传结构（plant population genetic structure）的变异，同时还检测了幼虫与成虫对来自这些种群的苜蓿叶片的响应。研究结果显示，L. melissa对苜蓿的区域定殖模式可通过植物化学变异得到良好预测，且已被定殖的苜蓿斑块展现出相近的个体间植物化学多样性水平。不过，尽管取食不同苜蓿种群植株的幼虫存活率和体重增长存在显著差异，植物化学变异却无法有效预测幼虫生长表现（larval performance）。此外，我们还观察到一类不匹配现象：支持最优幼虫生长表现的苜蓿种群与产卵雌虫（ovipositing females）偏好的苜蓿种群并不一致。综上，与L. melissa互作相关的植物变异维度取决于植食性昆虫的生活史阶段，这为理解具有复杂生活史（complex life history）的生物如何适应全新资源提出了重要的科学议题。