Aggressiveness of Males and Females of the Stag Beetle, Prosopocoilus inclinatus (Coleoptera: Lucanidae), are Mediated by Different Biogenic-amines

Abstract

Males of stag beetles have a pair of enlarged mandibles and combat with other males to defend a food site to where females will come to feed. The winner can monopolize mating with females came. However, to combat with an opponent, a male must show aggressiveness to the opponent. Females also take a similar aggressive posture with males. Recently, it has been shown that the degree of aggressiveness in insects is mediated by biogenic amines in the brain. Here, we report that the different amine pathways mediate the aggressiveness of males and females of a stag beetle, Prosopocoilus inclinatus. In males, dopamine rose up the degree of aggressiveness with concentration of the chemical, and a dopamine antagonist suppressed this effect with its concentration, indicating the mediation of the aggressiveness through the dopamine pathway. Whereas, aggressiveness of females was rose up by octopamine and was lowered by thyramine with the agent's concentrations. An octopamine antagonist showed a concentrationdependent suppression of octopamine's effect. Our results suggest that aggressiveness mediation of the males and the females had evolved independently for different benefits, and thus both the sexes have different mediation pathways for their aggressiveness.