The Development of Strain Typical Defensive Patterns in the Play Fighting of Laboratory Rats

During play fighting, rats attack and defend the nape, which if contacted is nuzzled with the snout. While all strains of rats can use all defensive tactics to protect the nape, there are strain-typical preferences for using particular tactics This study tests two hypotheses for this strain difference: (1) that each strain has strain-specific thresholds for each tactic, or (2) that each strain attacks differently which leads to strain differences in which defense tactics are used. Juvenile Long-Evans and Sprague-Dawley males were tested with both unfamiliar (experiment 1) and familiar (experiment 2) same-strain and different-strain partners. Experiment two was conducted to determine if familiarity with a different strain might allow rats to modify their strain-typical pattern of play. If hypothesis (1) were true, they would maintain strain-typical defense patterns irrespective of partner strain, whereas for (2) it would vary with partner strain. Hypothesis (1) was supported in the first experiment; all the rats maintained their strain-typical patterns regardless of the partner’s strain. However, the second experiment supported neither hypothesis, as each animal displayed strain-divergent behavior when playing with partners of a different strain as well as with partners of the same strain. Given that in the second experiment subjects were reared in mixed-strain groups, it is possible that, during the early juvenile period, animals are susceptible to discordant social experience