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

Many 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 fungus Rickia wasmannii influences the behaviour of Myrmica
ants 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 of n-C23 might
underlie the facilitated acceptance of infected non-nestmates. To test
this, we mimicked fungal infection in M. scabrinodis by applying synthetic
n-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. Adding n-C23 to uninfected corpses resulted in reduced
aggression in uninfected ants. This supports the hypothesis that n-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.