Non-lethal fungal infection could reduce aggression towards strangers in ants

Abstract

AbstractMany parasites interfere with the behaviour of their hosts. In social animals, such as ants, parasitic interference can cause changes on the level of the individual and also on the level of the society. The ant-parasitic fungusRickia wasmanniiinfluences the behaviour ofMyrmicaants by expanding the host’s nestmate recognition template, thereby increasing the chance of the colony accepting infected non-nestmates. Infected ants consistently show an increase of the alkane tricosane (n-C23) in their cuticular hydrocarbon profiles. Although experimental application of single compounds often elicits aggression towards manipulated ants, we hypothesized that the increase ofn-C23 might underlie the facilitated acceptance of infected non-nestmates. To test this, we mimicked fungal infection inM. scabrinodisby applying syntheticn-C23 to fresh ant corpses and observed the reaction of infected and uninfected workers to control and manipulated corpses. Infected ants appeared to be more peaceful towards infected but not uninfected non-nestmates. Addingn-C23 to uninfected corpses resulted in reduced aggression in uninfected ants. This supports the hypothesis thatn-C23 acts as a ‘pacifying’ signal. Our study indicates that parasitic interference with the nestmate discrimination of host ants might eventually change colony structure by increasing genetic heterogeneity in infected colonies.