Data from: Disease ecology across soil boundaries: effects of below-ground fungi on above-ground host–parasite interactions

Host–parasite interactions are subject to strong trait-mediated indirect effects from other species. However, it remains unexplored whether such indirect effects may occur across soil boundaries and connect spatially isolated organisms. Here, we demonstrate that, by changing plant (milkweed Asclepias sp.) traits, arbuscular mycorrhizal fungi (AMF) significantly affect interactions between a herbivore (the monarch butterfly Danaus plexippus) and its protozoan parasite (Ophryocystis elektroscirrha), which represents an interaction across four biological kingdoms. In our experiment, AMF affected parasite virulence, host resistance and host tolerance to the parasite. These effects were dependent on both the density of AMF and the identity of milkweed species: AMF indirectly increased disease in monarchs reared on some species, while alleviating disease in monarchs reared on other species. The species-specificity was driven largely by the effects of AMF on both plant primary (phosphorus) and secondary (cardenolides; toxins in milkweeds) traits. Our study demonstrates that trait-mediated indirect effects in disease ecology are extensive, such that below-ground interactions between AMF and plant roots can alter host–parasite interactions above ground. In general, soil biota may play an underappreciated role in the ecology of many terrestrial host–parasite systems.宿主与寄生虫的互作极易受到其他物种介导性状的间接效应影响。然而，此类间接效应是否能够跨越土壤边界，连接空间上隔离的生物类群，目前仍未得到探索。本研究通过调控植物（马利筋属*Asclepias* sp.）的性状，证实丛枝菌根真菌（arbuscular mycorrhizal fungi, AMF）可显著影响草食动物——黑脉金斑蝶（*Danaus plexippus*）与其原生动物寄生虫*Ophryocystis elektroscirrha*之间的互作，该互作跨越了四个生物界。在本实验中，AMF可影响寄生虫的毒力、宿主的抗性以及宿主对寄生虫的耐受力。上述效应同时依赖于AMF的密度与马利筋的物种种类：AMF会间接加重部分马利筋宿主上饲养的斑蝶的病害程度，却能减轻另一类马利筋宿主上饲养斑蝶的病害。这种物种特异性主要由AMF对植物初级（磷元素）与次级（强心苷*cardenolides*，马利筋中的毒素）性状的调控作用所驱动。本研究证实，性状介导的间接效应在疾病生态学中广泛存在，即AMF与植物根系之间的地下互作可改变地上的宿主-寄生虫互作。总体而言，土壤生物群落在多数陆生宿主-寄生虫系统的生态学过程中所发挥的作用，可能长期被低估。