Elevated atmospheric concentrations of carbon dioxide reduce monarch tolerance and increase parasite virulence by altering the medicinal properties of milkweeds

Hosts combat their parasites using mechanisms of resistance and tolerance, which together determine parasite virulence. Environmental factors, including diet, mediate the impact of parasites on hosts, with diet providing nutritional and medicinal properties. Here, we present the first evidence that ongoing environmental change decreases host tolerance and increases parasite virulence through a loss of dietary medicinal quality. Monarch butterflies use dietary toxins (cardenolides) to reduce the deleterious impacts of a protozoan parasite. We fed monarch larvae foliage from four milkweed species grown under either elevated or ambient CO2, and measured changes in resistance, tolerance, and virulence. The most high-cardenolide milkweed species lost its medicinal properties under elevated CO2; monarch tolerance to infection decreased, and parasite virulence increased. Declines in medicinal quality were associated with declines in foliar concentrations of lipophilic cardenolides. Our results...

宿主通过抗性与耐受两种机制对抗寄生虫，二者共同决定寄生虫的致病力。包括饮食在内的环境因素可调控寄生虫对宿主的影响，而饮食兼具营养与药用双重属性。本研究首次提供证据表明：持续的环境变化会通过降低饮食的药用品质，削弱宿主的耐受能力并增强寄生虫的致病力。帝王蝶借助膳食毒素（强心苷（cardenolides））来减轻一种原生动物寄生虫带来的有害影响。本研究将分别取自在升高CO₂浓度与背景CO₂浓度环境下培育的四种马利筋属植物的叶片，喂食帝王蝶幼虫，并测定了宿主抗性、耐受能力以及寄生虫致病力的变化。强心苷含量最高的马利筋物种在升高CO₂浓度下丧失了其药用属性；帝王蝶对感染的耐受能力下降，而寄生虫的致病力则有所增强。药用品质的下降与叶片中亲脂性强心苷浓度的降低显著相关。本研究结果……