Pupal cocoons affect sanitary brood care and limit fungal infections in ant colonies Journal Article

Author(s): Tragust, Simon; Ugelvig, Line V; Chapuisat, Michel; Heinze, Jürgen; Cremer, Sylvia
Article Title: Pupal cocoons affect sanitary brood care and limit fungal infections in ant colonies
Affiliation IST Austria
Abstract: 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.
Keywords: social immunity; hygienic behaviour; grooming; Formicidae; Metarhizium fungus; Sanitary brood care
Journal Title: BMC Evolutionary Biology
Volume: 13
Issue 1
ISSN: 1471-2148
Publisher: BioMed Central  
Date Published: 2013-01-01
Start Page: Article number: 225
Copyright Statement: CC-BY
DOI: 10.1186/1471-2148-13-225
Notes: The study was funded by the European Research Council (Marie Curie ERG 036569 and ERC Starting Grant 243071, both to SC; Marie Curie IEF 302204 to LVU), the Swiss National Science Foundation (SNSF 31003A-125306 to MC), and the German Research Foundation (DFG CR118/2, to SC).
Open access: yes (OA journal)