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涵盖竞争排斥（competitive exclusion）至促进作用（facilitation），可调控群落结构与动态变化。新发病原体（emergent pathogens）具备极大改变群落相互作用的潜力。本研究发现，一种新发昆虫病原真菌（fungal entomopathogen）在森林食叶害虫舞毒蛾（Lymantria dispar）的种群中，取代了原本占优势的致死性寄生生物类群。该寄生生物群落由该真菌、4种仅在杀死宿主后方能成功发育的寄生蜂物种（parasitoid species），以及一种可在宿主死亡前产生有活力的繁殖体（viable propagules）的病毒组成。研究团队对一个低密度样点开展了长达17年的连续采样，并将其与涵盖不同宿主密度梯度（包括种群暴发（outbreaks））的66个样点进行对比分析。由于该新发真菌病原与竞争的寄生蜂均需杀死宿主才能完成发育，二者极少在单个宿主体内发生共侵染（co-infection）。该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物种实现成功共侵染；事实上，病毒与一种携带多分DNA病毒（polydnavirus）的寄生蜂物种之间存在促进作用。这种由新发病原体改造形成的新型寄生生物群落，其形成机制同时受两个因素调控：一是寄生生物对宿主密度的响应，二是各寄生生物在单个宿主体内共栖的相对能力。