Onset of fights and mutual assessment in ant founding queens

In animals, the progress and outcomes of contests can be influenced by an individual's own condition, its opponent's condition or a combination of both. The use of chemical information to assess the quality of rivals has been underestimated despite its central role in the regulation of social interactions in many taxa. Here, we studied pairwise contests between founding queens of the ant Lasius niger to investigate whether the decision to engage in agonistic interactions relies on self or mutual assessment. Queens modulated their aggressive behaviours depending both on their own status and their opponent's status. We showed no influence of lipid stores or size on the onset of fights. However, differences in cuticular chemical signatures linked to fertility status accurately predicted the probability of behaving aggressively in pairs. Our study thus suggests that ant queens could rely on mutual assessment via chemical cues to make informed decisions about fight initiation.