Asymmetry in antennal contacts during trophallaxis in ants.

Behavioural and brain left-right asymmetries are a common feature among the animal kingdom. Lateralization often manifests itself at the population-level with most individuals showing the same direction of lateral bias. Theoretical model based on evolutionary stable strategy predicts that lateralization at the population-level is more likely to characterize social rather than solitary species. Empirical data supporting this hypothesis has been recently obtained in Hymenoptera showing that eusocial honeybees present an asymmetrical use of the antennae: the right antenna is involved in olfactory learning and present more olfactory receptors. However, no evidences about the role of antennal asymmetries in social interactions have been provided so far. Highly social ant species belonging to Formica rufa group are a good model for investigating natural communication because they are able to pass exact information to their nest mates. We applied the "binary tree" experimental paradigm, which allowed us to observe different types of antennal contacts performed by ants out of their nest. To examine possible asymmetrical use of the right and left antenna, we focused on "feeding" (the simplest) contacts where a "donor" ant is exchanging food with a "receiver" ant through trophallaxis. We observed a population-level asymmetry, with the "receiver" ant using the right antenna significantly more often than the left antenna. This study provides the first evidence of lateralization in antennal contacts in ants, and seems to support the hypothesis of mathematical models on the evolution of lateralization suggesting that the alignment of lateralization at the population-level matters in social interactions.