Gonadal hormones and aggression toward juvenile conspecifics in prairie deer mice

Summary

• 1. It was tested whether gonadal hormones regulate aggression directed toward juvenile conspecifics by adult prairie deer mice (Peromyscus maniculatus). Aggression was measured by counting the number of wounds on the underside of the skin of juveniles that had been paired overnight with unfamiliar adults. One experiment also included direct observations of fighting behavior.

• 2. Adult deer mice readily attacked juveniles. Under the testing conditions employed there was no difference in aggression as a function of sex of the adult, rearing condition (one vs five animals per cage) of the adult, or sex of the juvenile (Table 1).

• 3. Castrated adult males wounded juveniles less severely than did intact males (Table 2, P<0.02). The extent to which adult females wounded juveniles was not influenced by ovariectomy. Gonadectomy reduced body growth in both males (P<0.001) and females (P<0.03).

• 4. Pellets of testosterone propionate were implanted beneath the skin of castrated males. As measured by both wounding scores and the frequency of observed attacks, the aggression of these castrates toward juvenles was increased by hormone treatment (Table 3, P<0.05) to a level comparable with that of intact males. Thus, it is concluded that androgenic hormone secreted by the testes regulates aggression directed toward juveniles by adult male deer mice.