Co-founding ant queens prevent disease by performing prophylactic undertaking behaviour

Abstract

BackgroundSocial insects form densely crowded societies in environments with high pathogen loads, but have evolved collective defences that mitigate the impact of disease. However, colony-founding queens lack this protection and suffer high rates of mortality. The impact of pathogens may be exacerbated in species where queens found colonies together, as healthy individuals may contract pathogens from infectious co-founders. Therefore, we tested whether ant queens avoid founding colonies with pathogen-exposed conspecifics and how they might limit disease transmission from infectious individuals.ResultsUsing Lasius niger queens and a naturally infecting fungal pathogen Metarhizium brunneum, we observed that queens were equally likely to found colonies with another pathogen-exposed or sham-treated queen. However, when one queen died, the surviving individual performed biting, burial and removal of the corpse. These undertaking behaviours were performed prophylactically, i.e. targeted equally towards non-infected and infected corpses, as well as carried out before infected corpses became infectious. Biting and burial reduced the risk of the queens contracting and dying from disease from an infectious corpse of a dead co-foundress.ConclusionsWe show that co-founding ant queens express undertaking behaviours that, in mature colonies, are performed exclusively by workers. Such infection avoidance behaviours act before the queens can contract the disease and will therefore improve the overall chance of colony founding success in ant queens.Electronic supplementary materialThe online version of this article (10.1186/s12862-017-1062-4) contains supplementary material, which is available to authorized users.

Behaviours indicating cannibalistic necrophagy in ants are modulated by the perception of pathogen infection level

“…Moreover, these corpses were often torn apart or cleaned with formic acid that has strong antifungal and generally antibiotic properties; therefore, it is a very good substance for pathogen control and removal 24 , 66 . Tearing apart corpses can reduce the size of the suitable environment for the development of the infecting agent and facilitate the treatment of the infected parts with antibacterial secretions 19 , 24 , 51 , 77 , 78 . This behaviour can be analogous to the already mentioned destructive disinfection of pupae during the incubation period of the fungal pathogen 24 .…”

Colony co-founding in ants is an active process by queens

“…Although it cannot entirely be excluded, this scenario seems unlikely in L. niger since (i) queens sampled in different parts of Europe have been observed to group together in the laboratory [e.g. 42,[54][55][56][57][58][59][60] ] and (ii) collaboration among queens is unstable and always transforms into intense fighting when the first workers emerge, a phase that only a single queen survives.…”

Managing the risks and rewards of death in eusocial insects

“…Queens do not perform non-reproductive activities in mature colonies, but in newly founded colonies where worker helpers are not available, they engage in tasks of corpse disposal. This has been documented in a fungus-growing termite, P. spiniger , and an ant, L. niger [ 41 , 151 ]. In L. niger , biting and burying dead co-foundresses by queens when removal from closed nests is restricted [ 151 ] illustrates how nest structure and environmental conditions can play a role in behavioural plasticity.…”

“…This has been documented in a fungus-growing termite, P. spiniger , and an ant, L. niger [ 41 , 151 ]. In L. niger , biting and burying dead co-foundresses by queens when removal from closed nests is restricted [ 151 ] illustrates how nest structure and environmental conditions can play a role in behavioural plasticity. When disposing of corpses outside is restricted due to factors such as nest blockage, flooding or freezing, alternative behaviours such as burial or cannibalism are expected.…”