Same-sex mounting in single-housed C57BL/6J female mice is not regulated by estrous state

Female-female mounting is widespread in mammals. Although the behavioral functions of female-female mounting likely vary according to species and to behavioral context, a large body of work has investigated the relationship of female-female mounting to female sexual receptivity and hormonal status. While this relationship has been extensively explored in female rats, fewer instances of female-female mounting have been described in mice, and correspondingly, less is known about the potential relationship in mice between female-female mounting and estrous state. Recently, we found that short-term social isolation robustly promotes same-sex mounting in C57BL/6J female mice. In the current study, we tested whether displays of female-female mounting by naturally cycling 3-days-single-housed females during interactions with naturally cycling, group-housed stimulus females are related to estrous state. We found no evidence that same-sex mounting by single-housed females is related to the estrous state of either female in the pair. These findings suggest that same-sex mounting displayed by single-housed female mice is not related to female sexual behavior, and future work remains to determine the functions of female-female mounting in this species and behavioral context.