Data from: Food plant-derived disease tolerance and resistance in a natural butterfly-plant-parasite interaction

Organisms can protect themselves against parasite-induced fitness costs through resistance or tolerance. Resistance includes mechanisms that prevent infection or limit parasite growth while tolerance alleviates the fitness costs from parasitism without limiting infection. Although tolerance and resistance affect host-parasite coevolution in fundamentally different ways, tolerance has often been ignored in animal-parasite systems. Where it has been studied, tolerance has been assumed to be a genetic mechanism, unaffected by the host environment. Here we studied the effects of host ecology on tolerance and resistance to infection by rearing monarch butterflies on twelve different species of milkweed food plants and infecting them with a naturally occurring protozoan parasite. Our results show that monarch butterflies experience different levels of tolerance to parasitism depending on the species of milkweed that they feed on, with some species providing over two-fold greater tolerance than other milkweed species. Resistance was also affected by milkweed species, but there was no relationship between milkweed-conferred resistance and tolerance. Chemical analysis suggests that infected monarchs obtain highest fitness when reared on milkweeds with an intermediate concentration, diversity and polarity of toxic secondary plant chemicals known as cardenolides. Our results demonstrate that environmental factors – such as interacting species in ecological food webs – are important drivers of disease tolerance.

生物体可通过抗性（resistance）与耐受（tolerance）两种策略，抵御寄生虫诱导的适合度代价。抗性指通过各类机制阻断感染或抑制寄生虫增殖；而耐受则是在不限制寄生虫感染的前提下，减轻寄生作用带来的适合度损失。尽管抗性与耐受对宿主-寄生虫协同进化的影响机制存在本质差异，但在动物-寄生虫研究体系中，耐受常被忽视。即便已有相关研究，耐受也常被假定为一种不受宿主环境影响的遗传机制。本研究以帝王蝶为实验对象，将其饲养于12种不同的马利筋（milkweed）属食源植物上，并以天然存在的原生动物寄生虫进行感染，以此探究宿主生态学特征对宿主感染抗性与耐受能力的影响。研究结果显示，帝王蝶的寄生耐受水平因取食的马利筋物种不同而存在显著差异，部分马利筋物种可使帝王蝶的耐受水平较其他物种提升两倍以上。马利筋物种同样会影响宿主的抗寄生虫抗性，但马利筋介导的抗性与耐受之间未发现显著关联。化学分析结果表明，被感染的帝王蝶在取食含有中等浓度、多样性与极性的有毒次生植物化学物质——强心苷（cardenolides）的马利筋时，可获得最优的适合度表现。本研究结果证实，生态食物网中的互作物种等环境因素，是疾病耐受的重要驱动因子。