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，同种寄主植物并非完全一致；寄主植物的营养品质与防御能力存在种内变异，这可能介导植物-昆虫互作中出现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*）向外来寄主植物苜蓿（alfalfa, *Medicago sativa*）持续进行的寄主范围扩张过程，探究了这一可能性。我们选取了7个被梅利莎蓝蝶定殖程度存在差异的苜蓿种群开展实验，具体分析了这些种群的植物化学组成、叶片蛋白含量以及种群遗传结构差异，同时测定了蝶幼虫与成虫对取自同一苜蓿种群叶片的响应。结果显示，梅利莎蓝蝶对苜蓿的区域定殖模式可通过植物化学变异得到较好预测，且已被定殖的苜蓿种群间的个体间植物化学多样性水平相近。然而，尽管取食不同苜蓿种群叶片的蝶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表现。此外，我们还观察到：支持最优幼虫生长性能的苜蓿种群与产卵雌虫偏好的苜蓿种群之间存在显著不匹配。综上，调控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，这为理解具有复杂生活史的生物如何适应新型寄主资源提供了重要研究方向。