Changes in the levels of biogenic amines associated with aggressive behavior of queen in the social parasite ant Vollenhovia nipponica

Abstract

Insect behavior is regulated by physiological and neurological systems. Biogenic amines play a role in motivating the behavior as neurotransmitters, neuromodulators, and neurohormones in the nervous systems. In ants, the change of brain amine levels is linked to various behavioral properties: reproduction, cooperation, and hostility. Aggressiveness is also manipulated by the neurological systems. The social structures in some ant species are established by aggressive interactions among queens. However, there are a few cases showing the putative role of biogenic amines for the queen aggression. Vollenhovia nipponica is a social parasite ant, which establishes functional monogyny that antagonistic interactions among multiple queens lead to dominance hierarchy. In this time, we examined changes in the levels of biogenic amines in heads of queens in V. nipponica, associated with the observation of aggressive behavior. In the colonies, dealate queens violently attacked toward each other by biting and pulling on body parts. Whereas, the aggressive behavior was never observed in alate queens. In the measurements in four biogenic amines, serotonin (5-HT), dopamine (DA), octopamine (OA), and tyramine (TA), the levels of 5-HT and DA in dealates were significantly higher than those in alates. The levels of OA and TA were not significantly different between them. Moreover, the similar changes were confirmed in the groups of young (10–30 days old) and old queens (more than 6-month old). In V. nipponica queens, 5-HT and DA could regulate motivation of aggression, irrespective of age. However, the changes of biogenic amines are possibly affected by other behavioral factors.