Partner Choice and Context‐Dependent Sex Differences in Rat Rough‐and‐Tumble Play

Rough-and-tumble play (RTP) is the form of play most often observed in juvenile mammals. In rats, RTP typically consists of competing for access to the partner's nape, with both sex and social contexts influencing its frequency and structure. Although most studies employ dyadic tests, this design limits partner choice. Here, we investigated sex differences in partner preference and play frequency in Wistar rats using a group play paradigm. Juvenile rats were tested in mixed-sex and same-sex triads, allowing individuals to select partners. We measured playful nape attacks, defensive responses, and the distribution of play across partners. Results revealed that both sexes formed partner preferences, but only males exhibited sex-based preferences, directing significantly more playful attacks toward females than males. Female rats showed no group-level sex preference, though most individuals displayed consistent preferences for one partner, often, but not exclusively, for the male partner. Importantly, females initiated fewer nape attacks than males in mixed-sex groups, but this sex difference disappeared in all-female groups, where females initiated playful attacks at levels comparable to males. Thus, sex differences in RTP frequency were context dependent, emerging only when females were tested alongside males. These findings demonstrate two distinct forms of sex differences in the play of rats: partner choice and play frequency. Whereas males preferentially engage with females, females appear more flexible, forming idiosyncratic preferences independent of the partner's sex. Moreover, female play initiation is particularly sensitive to social context, highlighting the importance of group-based testing for understanding naturalistic social decision-making.