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）或耐受力（tolerance）抵御寄生虫诱导的进化适合度代价：抗性指可阻止感染或限制寄生虫增殖的防御机制，而耐受力则可在不抑制寄生虫感染的前提下，缓解寄生作用带来的宿主进化适合度损失。尽管耐受力与抗性对宿主-寄生虫协同进化的影响存在本质区别，但在动物-寄生虫系统中，耐受力常被忽略。在已开展的相关研究中，耐受力通常被假定为不受宿主环境干扰的遗传机制。本研究以黑脉金斑蝶为实验对象，将其饲养于12种不同的马利筋食源植物上，并以自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寄生感染的耐受力与抗性的影响。研究结果显示，黑脉金斑蝶的寄生耐受力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力提升两倍以上。同时，马利筋物种也会对宿主的抗性产生显著影响，但马利筋所赋予的宿主抗性与耐受力之间并未发现显著关联。化学分析表明，受感染的黑脉金斑蝶在取食含有中等浓度、多样性和极性的被称为强心苷（cardenolides）的植物次生有毒化学成分的马利筋时，可获得最高的进化适合度。本研究结果证实，诸如生态食物网中互作物种这类环境因素，是影响疾病耐受力的重要驱动因素。