Wood ants use resin to protect themselves against pathogens

Abstract

Social life is generally associated with an increased exposure to pathogens and parasites, due to factors such as high population density, frequent physical contact and the use of perennial nest sites. However, sociality also permits the evolution of new collective behavioural defences. Wood ants, Formica paralugubris, commonly bring back pieces of solidified coniferous resin to their nest. Many birds and a few mammals also incorporate green plant material into their nests. Collecting plant material rich in volatile compounds might be an efficient way to fight bacteria and fungi. However, no study has demonstrated that this behaviour has a positive effect on survival. Here, we provide the first experimental evidence that animals using plant compounds with antibacterial and antifungal properties survive better when exposed to detrimental micro-organisms. The presence of resin strongly improves the survival of F. paralugubris adults and larvae exposed to the bacteria Pseudomonas fluorescens, and the survival of larvae exposed to the entomopathogenic fungus Metarhizium anisopliae. These results show that wood ants capitalize on the chemical defences which have evolved in plants to collectively protect themselves against pathogens.

Pathogen-associated self-medication behavior in the honeybee Apis mellifera

“…Wood ants (Formica paralugubris) incorporate pieces of solidified conifer resin into their nests. Resin inhibits growth of bacteria and fungi in nest material and protects the ants against harmful microorganisms (Christe et al 2003;Chapuisat et al 2007). However, by measuring immune response, the prophenoloxidase activity (part of the humoral innate immune response of insects) was very low and not affected by the presence of resin.…”

Implications of the behavioural immune system for social behaviour and human health in the modern world

“…Even under conditions in which there is no perceptual evidence of infectious agents in the immediate environment, organisms may engage in behaviours that proactively manage a latent infection risk, thereby reducing the likelihood that this latent risk becomes manifest in ways that would require reactive avoidance. Examples include ants' use of antibiotic resins to line their nests [13] and, as we discuss in greater detail below, humans' efforts to maintain existing cultural norms [14]. Collectively, these strategies have been likened to a kind of 'social immune system' [2] or 'behavioural immune system' [5,15,16].…”

The behavioural immune system and the psychology of human sociality

“…Some forms of behavioural defence-such as cytokineinduced sickness behaviour [8,9] and self-medication [10,11]-are reactive, rather than proactive. But there is also abundant evidence of proactive behavioural defence as well: wood ants collect pieces of coniferous resin as a prophylactic defence against bacteria and pathogenic fungi [12]; bullfrog tadpoles selectively avoid swimming near infected tadpoles [13]; female mice respond aversively to the odours of male mice infected with nematode parasites [14]; chimpanzees avoid social contact with (and may even respond aggressively towards) other chimpanzees infected with polio [15]. In short, just as the 'real' immune system is characterized by mechanisms that facilitate adaptive immunological responses to pathogens that enter the body, the behavioural immune system is characterized by mechanisms that facilitate adaptive psychological responses to perceptual cues connoting the presence of pathogens in the immediate perceptual environment-including the presence of pathogens in conspecifics.…”