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）并非完全一致；寄主植物的种内变异（intraspecific variation）在营养质量或防御能力上的差异，可能会介导植物-昆虫互作（plant-insect interactions）中呈现空间异质性的交互结局。本研究以本土蝴蝶梅利莎蓝蝶（Melissa blue, *Lycaeides melissa*）正向外来寄主植物苜蓿（alfalfa, *Medicago sativa*）拓展寄主范围（host breadth expansion）这一正在进行的现实场景为背景，探究上述可能性。我们针对7个被梅利莎蓝蝶定殖程度存在差异的苜蓿种群开展变异分析；具体检测指标涵盖植物化学组成（phytochemistry）、叶蛋白（foliar protein）含量及植物种群遗传结构（plant population genetic structure），同时探究了幼虫（caterpillars）与成虫（adult butterflies）对同种群苜蓿叶片的响应。梅利莎蓝蝶对苜蓿的区域定殖模式，可通过植物化学组成变异得到良好预测；且已被定殖的苜蓿斑块，其个体间植物化学多样性（inter-individual phytochemical diversity）水平较为一致。然而，植物化学组成变异对幼虫生长表现（larval performance）的预测效果不佳——尽管取食不同苜蓿种群植株的幼虫，其存活率（survival）与体重增长（weight gain）存在显著差异。此外，本研究还发现：支持幼虫最优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匹配。因此，介导梅利莎蓝蝶与寄主植物互作的植物变异维度，取决于植食性昆虫的生活史阶段（life history stage）；这为理解具有复杂生活史（complex life history）的生物如何适应新型寄主资源，提出了值得深入探讨的科学问题。