Abstract
Thirty-two colonies composed of one female and two male rats in each of the Tsukuba strains for high or low emotionality (THE or TLE) were formed and reared in wooden enclosures for about two months. During this period, intruder tests and intra-colony observations were conducted once a week, and several measures of social behaviors were obtained through VTR observations. A dominant male of each colony was identified based on its attacks on an intruder rat at the last two testings. In intruder tests, the dominant TLE males attacked intruders more severly than the ones in the THE. Although the subordinate TLE males also attacked intruders on a half level with dominants of the same strain, the subordinates of the THE scarcely attacked intruders. The strain×dominance interaction was found significant. During intra-colony observations, the subordinates of the THE exhibited significantly more abnormal homosexual behaviors than those of the TLE. On the other hand, the TLE males showed significantly more normal sexual behaviors than the THE males. These findings were discussed in terms of social context in their colonies.
