Recognition in ants: social origin matters.

Joël Meunier,Olivier Delémont,Christophe Lucas

doi:10.1371/journal.pone.0019347

Abstract

The ability of group members to discriminate against foreigners is a keystone in the evolution of sociality. In social insects, colony social structure (number of queens) is generally thought to influence abilities of resident workers to discriminate between nestmates and non-nestmates. However, whether social origin of introduced individuals has an effect on their acceptance in conspecific colonies remains poorly explored. Using egg-acceptance bioassays, we tested the influence of social origin of queen-laid eggs on their acceptance by foreign workers in the ant Formica selysi. We showed that workers from both single- and multiple-queen colonies discriminated against foreign eggs from single-queen colonies, whereas they surprisingly accepted foreign eggs from multiple-queen colonies. Chemical analyses then demonstrated that social origins of eggs and workers could be discriminated on the basis of their chemical profiles, a signal generally involved in nestmate discrimination. These findings provide the first evidence in social insects that social origins of eggs interfere with nestmate discrimination and are encoded by chemical signatures.

Highlights

The evolution of sociality requires recognition mechanisms allowing group members to direct cooperative or aggressive behaviours towards the correct individuals
Our egg-acceptance bioassays provide the first evidence in social insects that social origin of queen-laid eggs is associated with cues that interfere with nestmate discrimination
All F. selysi workers discriminated against foreign monogyne eggs, whereas they did not discriminate between nestmate and foreign polygyne ones

Summary

Introduction

The evolution of sociality requires recognition mechanisms allowing group members to direct cooperative or aggressive behaviours towards the correct individuals. The presence of multiple resident queens is predicted to broaden the mix of genetically determined chemical cues composing the colony-profile, which in turn is expected to increase discrimination errors between nestmate and non-nestmates individuals, and to inhibit aggression against conspecific foreigners [8], but see [9]. Chemical analyses suggested that discrimination between intruders from alternative social origins could be based on chemical profiles, as S. invicta queens and M. barbatus workers present subtle differences of chemical profiles when originating from monogyne and polygyne colonies [19], [20]. Our present study was conducted in the ant F. selysi (i) to test the influence of social origin of eggs on their acceptance by foreign workers, and (ii) to investigate the association between chemical profiles and social origins of workers and eggs. We determined whether social origin of eggs and workers could be discriminated on the basis of their chemical profiles by testing qualitative and quantitative differences between chemical profiles of individuals (i.e. eggs and workers) sampled in 23 monogyne and 23 polygyne field colonies

Materials and Methods

Results

Discussion