Utilization of same- vs. mixed-sex dyads impacts the observation of sex differences in juvenile social play behavior.

The study of juvenile social play behavior has gained popularity due to the disruption of social behaviors in several psychiatric illnesses. In contrast to many tests currently utilized in animal models of psychiatric illness, juvenile social play behavior is part of the normal behavioral repertoire in the laboratory rat and can be observed in a controlled setting but without evocation by the experimenter. Understanding sources of naturally occurring differences in the juvenile social play behavior of the rat is a fundamental first step to guide future research on identifying factors that disrupt this behavior. One of the most commonly found variations is a sex difference, with male rats displaying higher levels of rough-and-tumble play behavior relative to females. This sex difference is also observed in human play. In our recent paper published in Biology of Sex Differences, we investigated how the sex and familiarity of the play partner can impact different components of rough-and-tumble play behavior (pouncing, pinning, boxing, and chasing) and the observation of sex differences within each of these components. Our findings suggest that juvenile male rough-and-tumble play behavior is impacted by the sex of their play partner, while females are more sensitive to the familiarity of their play partner. In this review, we discuss our recent findings and provide a comprehensive comparison of methodology and the reporting of sex differences in the literature on this topic.