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）抵御寄生虫诱导的适合度代价。其中，抗性指可阻断感染或抑制寄生虫增殖的各类机制，而耐受性则是在不限制感染的前提下，减轻寄生作用带来的宿主适合度代价。尽管二者对宿主-寄生虫协同进化的影响机制存在本质差异，但在动物-寄生虫系统中，耐受性常被忽视。在已有相关研究中，耐受性通常被视为不受宿主环境影响的遗传机制。本研究通过将黑脉金斑蝶（monarch butterfly）饲养于12种不同的马利筋属食源植物，并令其感染一种天然存在的原生动物寄生虫（protozoan parasite），探究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，黑脉金斑蝶的寄生耐受性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宿主的耐受性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性，但马利筋介导的抗性与耐受性之间并无显著关联。化学分析结果表明，被感染的黑脉金斑蝶若取食的马利筋中，强心苷类（cardenolides）这类有毒次生植物代谢物的浓度、多样性与极性处于中等水平时，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，是调控疾病耐受性的重要驱动因子。