Data from: Pupal cocoons affect sanitary brood care and limit fungal infections in ant colonies

Background: The brood of ants and other social insects is highly susceptible to pathogens, particularly those that penetrate the soft larval and pupal cuticle. We here test whether the presence of a pupal cocoon, which occurs in some ant species but not in others, affects the sanitary brood care and fungal infection patterns after exposure to the entomopathogenic fungus Metarhizium brunneum. We use a) a comparative approach analysing four species with either naked or cocooned pupae and b) a within-species analysis of a single ant species, in which both pupal types co-exist in the same colony. Results: We found that the presence of a cocoon did not compromise fungal pathogen detection by the ants and that species with cocooned pupae increased brood grooming after pathogen exposure. All tested ant species further removed brood from their nests, which was predominantly expressed towards larvae and naked pupae treated with the live fungal pathogen. In contrast, cocooned pupae exposed to live fungus were not removed at higher rates than cocooned pupae exposed to dead fungus or a sham control. Consistent with this, exposure to the live fungus caused high numbers of infections and fungal outgrowth in larvae and naked pupae, but not in cocooned pupae. Moreover, the ants consistently removed the brood prior to fungal outgrowth, ensuring a clean brood chamber. Conclusion: Our study suggests that the pupal cocoon has a protective effect against fungal infection, causing an adaptive change in sanitary behaviours by the ants. It further demonstrates that brood removal - originally described for honeybees as “hygienic behaviour” – is a widespread sanitary behaviour in ants, which likely has important implications on disease dynamics in social insect colonies.

背景：蚂蚁及其他社会性昆虫的巢内未成熟子代对病原体具有高度易感性，尤其是那些可穿透柔软幼虫与蛹表皮的病原体。本研究旨在检验：部分蚂蚁物种特有的蛹茧（部分蚁类具有蛹茧，部分则无）是否会影响虫群暴露于虫生真菌（entomopathogenic fungus）布氏白僵菌（Metarhizium brunneum）后的卫生育幼行为与真菌感染模式。本研究采用两种研究方案：a）比较分析法，分析4种分别具有裸露蛹与茧包蛹的蚂蚁物种；b）种内分析法，选取1种同时存在两种蛹型的单一蚁类物种，其同巢内可同时存在裸露蛹与茧包蛹。结果：研究发现，蛹茧的存在并未削弱蚂蚁对真菌病原体的识别能力，且拥有茧包蛹的蚁类物种在暴露于病原体后，会提升对巢内子代的梳理行为。所有受试蚁类物种均会将受感染的子代移除出巢，该移除行为主要针对经活体真菌处理的幼虫与裸露蛹。与之相反，暴露于活体真菌的茧包蛹，其被移除的概率并未显著高于暴露于灭活真菌或假对照（sham control）的茧包蛹。与此一致的是，暴露于活体真菌会在幼虫与裸露蛹中引发大量感染与真菌菌丝长出，但茧包蛹未出现此类情况。此外，蚂蚁始终会在真菌菌丝长出前移除受感染子代，以此维持巢内育幼室的清洁。结论：本研究表明，蛹茧可抵御真菌感染，并促使蚂蚁的卫生行为产生适应性改变。本研究同时证实，最初在蜜蜂中被定义为“卫生行为（hygienic behaviour）”的子代移除行为，在蚂蚁中是一种广泛存在的卫生行为，这一发现或对社会性昆虫群体的疾病传播动态具有重要意义。