The effects of testosterone and scopolamine HBr on the aggressive behaviour of male voles, Microtus townsendii

Abstract

Two substances were shown to have a significant effect on the aggressive behaviour of male voles of the species Microtus townsendii in neutral arena dyadic encounters in the laboratory: testosterone was used to increase aggression in small males, and scopolamine HBr, an anticholinergic, was used to decrease it in large males. After the effects of these two substances on the behaviour of male voles in the laboratory had been determined, both were used in a field study of the role of social behaviour in the ecology of M. townsendii.Subadult males between 20 and 44 g, implanted subcutaneously with Silastic capsules containing testosterone, investigated each other less and fought more than control males with dummy implants. They also fought less than adult control males weighing 45 g or more. As expected, the onset of male aggression at sexual maturity in this species appears to be androgen dependant.Adult male M. townsendii weighing 45 g or more with implants containing scopolamine HBr fought significantly less than control males with dummy implants. Scopolamine HBr reduced intermale aggression very effectively whilst apparently not affecting coordinated motor activity.