Queen discrimination ability of ant workers (Camponotus japonicus) coincides with brain maturation

Discrimination behavior is a fundamental feature of social insects, and the discrimination ability allows the individual to be integrated into the colony. To address the brain functions associated with this task, which underlies intraspecific communication, I examined the ability to discriminate queens in young workers of the ant Camponotus japonicus together with a histological analysis of their brains. Workers raised in a foster colony were tested with respect to their ability to discriminate the foster queen from an unfamiliar queen. During the first 3 days after eclosing, some young workers made erroneous decisions whereas after 3-4 days the decisions were always correct. To assess brain maturation, mitotic activity in the brains of workers was individually analyzed using BrdU injection immediately after the behavioral test. Neurogenesis appeared to be complete at eclosion, but in 3 of 8 young workers that showed incorrect behavioral decisions, mitotic activity was observed in the antennal lobe. In contrast, no mitotic activity was observed in the brains of young workers who correctly discriminated their foster queens from alien queens. These results suggest that in newly emerged ant workers the ability to discriminate queens coincides with the completion of cell proliferation in the brain.