Abstract
A dead conspecific poses a potential pathogen risk for social animals. We have discovered that Argentine ants (Linepithema humile) prevent spread of pathogenic fungi from corpses by depositing the dead to combined toilet and refuse areas and applying pygidial gland secretion on them. The presence of a corpse in a nest increases this secretion behaviour. We identified three fungi growing on Argentine ant corpses. Growth of the Argentine ant pathogen Aspergillus nomius and the plant pathogen Fusarium solani on corpses was inhibited as long as the ants were constantly attending them as the ant anal secretion only delayed germination of their spores. In contrast, the effect of the ant anal secretion on the human pathogen Aspergillus fumigatus was much stronger: it prevented spore germination and, accordingly, the fungus no longer grew on the treated corpses. The Argentine ants are one of the world’s worst invasive alien species as they cause ecological and economical damage in their new habitats. Our discovery points at a novel method to limit Argentine ant colonies through their natural fungal pathogens.
Highlights
Social immune system is a term used to describe co-operative behaviour of social animals to reduce vulnerability to disease transmission that arises from living in a genetically homogenous closely interacting group[1]
We discovered that Argentine ants defecate and secrete pygidial gland content onto the corpses at the refuse piles and that this behaviour inhibits growth of pathogenic fungi
As it was earlier shown that black garden ants (Lasius niger) have separate toilet area and waste pile to where the corpses were laid[9], we studied where Argentine ants put their dead
Summary
Social immune system is a term used to describe co-operative behaviour of social animals to reduce vulnerability to disease transmission that arises from living in a genetically homogenous closely interacting group[1]. Management of corpses, faeces, and food waste is part of the social immune system to improve nest hygiene. Corpse management aims to prevent growth and spread of pathogens and parasites: for example, it has been shown in a laboratory experiment that a single fungal infected cadaver can be fatal to the whole ant colony[5]. In some highly socially organised insects corpse management has been suggested to be separate from the other basic cleaning activities, such as disposing faeces and food remains. Argentine ants deposit food waste and dead bodies onto refuse piles[22] yet their defecating behaviour has not been studied. We discovered that Argentine ants defecate and secrete pygidial gland content onto the corpses at the refuse piles and that this behaviour inhibits growth of pathogenic fungi
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