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.

生物可通过抗性（resistance）与耐受性（tolerance）抵御寄生虫引发的适合度代价。抗性指通过阻断感染或抑制寄生虫增殖的机制实现防御，而耐受性则是在不限制感染的前提下减轻寄生虫寄生带来的适合度代价。尽管耐受性与抗性对宿主-寄生虫协同进化的影响存在本质差异，但在动物-寄生虫系统中，耐受性常被忽视。即便已有相关研究，耐受性也常被视为一种不受宿主环境影响的遗传机制。本研究通过将帝王蝶饲养于12种不同的马利筋属（milkweed）食源植物，并使其感染一种自然存在的原生动物寄生虫，探究了宿主生态学对感染相关耐受性与抗性的影响。研究结果显示，帝王蝶对寄生作用的耐受性水平因取食的马利筋物种不同而异，部分马利筋物种所能提供的耐受性水平是其他物种的两倍以上。马利筋物种同样会影响宿主的抗性，但马利筋介导的抗性与耐受性之间并无关联。化学分析结果表明，当受感染的帝王蝶取食含有中等浓度、多样性及极性的强心甾（cardenolides）——一类有毒植物次生代谢物——的马利筋时，其适合度可达最高。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性的重要调控因子。