Evidence that chemical signals promote fighting between intact male hooded rats

Abstract

Male members of mixed-sex colonies of hooded rats were exposed to three types of same-age conspecific intruders: intact male (M), castrated male (C), and ovariectomized female (OVX). During the first 20 min after intruder introduction, colony males sniffed the anogenital region of C or OVX intruders more frequently and for longer durations than they sniffed that of M intruders. Twenty-one hours later, fewer C and OVX intruders had suffered wounds than M counterparts, and their wound scores were lower. OVX intruders were not rendered more susceptible to attack by painting their anogenital region with fresh M urine. These findings have implications for Adams' model of intermale fighting, and they indicate that onset of attack by male hooded rats is promoted by testosterone-related anogenital substance(s).