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.

Methods
The uploaded dataset contains four parts: three data sheet files (.csv) with (a) dyadic interaction assays between live individuals and corpses/dummies with different treatments originating from foreign colonies, infected or uninfected; (b) dyadic interaction assays between live individuals and corpses/dummies originating from the same colony as the live individuals - control tests; (c) chemical data referring to the relative abundance of n-C23 in the cuticular hydrocarbon profile (CHC-profile) of different samples, uninfected and infected; and (d) 10 chromatograms (.qgd files). In all cases, data originated from the ant species Myrmica scabrinodis. The details of the tests and the analyses are given in the provided preprint https://doi.org/10.21203/rs.3.rs-1305759/v1. The dyadic tests were performed in a blind manner.