Changes in Social Reactions Resulting from Early Experience with Another Species

28 mice were reared by rat-mothers and siblings from the age of 1 to 3 days, whereas controls were reared with mouse-mothers and siblings. When adults, both groups preferred their foster-species in a social-preference test. More aggression was directed toward a mouse-partner than toward a rat-partner in both groups. The mouse-reared group was generally more aggressive than the rat-reared group. The rat-reared group showed no aggression toward rats. Being reared by rats decreased the sexual behaviour toward mice. No copulation with small (prematurely oestrous) female rats occurred, but sexual interest was shown by the rat-reared mice. Aggressive responses toward the female partner occurred significantly more often when the female did not belong to the fostering species. No differences in open-field activity were found.