Partner Preference Strength is not Influenced by How Motivated Juvenile Male Rats are to Engage in Play Fighting

Rats frequently engage in rough-and-tumble play, and do so in pairs. However, when multiple partners are present, some individuals are preferred more than others. Rats that have been isolated from their peers show increased motivation to engage in rough-and-tumble play. When publishing papers on group play in rats, we have been asked by several reviewers whether the time spent in social isolation to increase play motivation inadvertently reduces partner preferences. To address this question, we investigated how varying periods of social isolation (0, 2.5, E. J. Marijke Achterberg212, and 24 h) influences partner preferences of focal Long Evans rats when interacting with one unfamiliar Long Evans partner and one unfamiliar Fischer 344 partner. Regardless of the degree to which the rats were motivated to play, partner preferences remained stable across isolation times. This suggests that the general drive to play is independent of the motivation to select a specific partner. Unexpectedly, the preference for same-strain partners was not as strong as in previous studies with larger groups, highlighting that group size and social context are critical factors that can alter social dynamics and potentially override established partner preferences. These findings underscore the importance of group composition in the study of social behavior and suggest that partner preferences may reflect stable social compatibilities rather than transient changes in play motivation.