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；二者间的相互作用范围从竞争排斥到互利易化，可驱动群落的结构与动态变化。新发病原体具备极大改变群落相互作用的潜力。本研究发现，一种新发真菌昆虫病原物（fungal entomopathogen）在森林食叶害虫舞毒蛾（Lymantria dispar）的种群中，取代原有致死性寄生生物成为优势类群。该寄生生物群落由该真菌、4种仅在杀死宿主后才能完成发育的寄生蜂类群，以及一种可在宿主死亡前产生有活力繁殖体的病毒构成。我们对一个低密度样点开展了长达17年的采样，并将其与涵盖不同宿主密度梯度（包括种群暴发期）的66个样点进行对比分析。由于每类寄生生物都必须杀死宿主才能完成发育，该新发真菌病原体与竞争性寄生蜂极少出现宿主个体共感染现象。病毒在低宿主密度样点中未被检出，但可与其余所有寄生生物类群成功实现共感染；事实上，病毒与一种携带多分DNA病毒（polydnavirus）的寄生蜂类群之间还存在互利易化作用。这个因新发病原体而重塑的新型寄生生物群落，其形成既受寄生生物对宿主密度的响应特征影响，也取决于各类寄生生物在同一宿主体内共存的相对能力。