Data from: Fatal diseases and parasitoids: from competition to facilitation in a shared host.

Diverse parasite taxa share hosts both at the population level and within individual hosts and their interactions, ranging from competitive exclusion to facilitation, can drive community structure and dynamics. Emergent pathogens have the potential to greatly alter community interactions. We found that an emergent fungal entomopathogen dominated pre-existing lethal parasites in populations of the forest defoliating gypsy moth, Lymantria dispar. The parasite community was composed of the fungus and four parasitoid species that only develop successfully after they kill the host, and a virus that produces viable propagules before the host has died. A low density site was sampled over 17 years and compared with 66 sites across a range of host densities, including outbreaks. The emergent fungal pathogen and competing parasitoids rarely co-infected host individuals because each taxa must kill its host. The virus was not present at low host densities, but successfully co-infected with all other parasite species. In fact there was facilitation between the virus and one parasitoid species hosting a polydnavirus. This newly formed parasite community, altered by an emergent pathogen, is shaped both by parasite response to host density and relative abilities of parasites to co-inhabit the same host individuals.多样的寄生生物类群既可在种群水平上共享宿主，也可在单个宿主体内共存；它们之间的相互作用从竞争排除到互利促进不等，可驱动群落结构与动态变化。新发病原物具有极大改变群落相互作用的潜力。我们的研究发现，一种新发昆虫病原真菌（fungal entomopathogen）在森林食叶害虫舞毒蛾（Lymantria dispar）种群中占据了预先存在的致死性寄生生物的优势地位。该寄生生物群落由该真菌、4种仅在杀死宿主后才能成功发育的寄生蜂类群，以及一种可在宿主死亡前产生有活力繁殖体的病毒组成。研究团队对一处低密度样地开展了长达17年的采样，并将其与涵盖不同宿主密度（包括虫灾暴发期）的66个样地进行对比。由于各类寄生生物均需杀死宿主才能完成发育，该新发真菌病原与竞争关系的寄生蜂极少出现共感染宿主个体的情况。该病毒在低密度宿主种群中未被检出，但可与其余所有寄生生物类群成功实现共感染；实际上，该病毒与一种携带有多分DNA病毒（polydnavirus）的寄生蜂类群之间存在互利促进作用。这个因新发病原物而重塑的新型寄生生物群落，其形成同时受寄生生物对宿主密度的响应，以及各类寄生生物共同栖息于同一宿主体内的相对能力所调控。