Rates of female mouse ultrasonic vocalizations are low and are not modulated by estrous state during interactions with muted males.

Adult male mice produce high rates of ultrasonic vocalizations (USVs) during courtship interactions with females. It was long thought that only males produced courtship USVs, but recent studies using microphone arrays to assign USVs to individual signalers report that females produce a portion (5-18%) of total courtship USVs. The factors that regulate female courtship USV production are poorly understood. Here, we tested the idea that female courtship USV production is regulated by estrous state. To facilitate the detection of female USVs, we paired females with males that were muted for USV production via caspase-mediated ablation of midbrain neurons that are required for USV production. We report that total USVs recorded during interactions between group-housed B6 females and muted males are low and are not modulated by female estrous state. Similar results were obtained for single-housed B6 females and for single-housed outbred wild-derived female mice paired with muted males. These findings suggest either that female mice produce substantial rates of courtship USVs only when interacting with vocal male partners or that prior studies have overestimated female courtship USV production. Studies employing methods that can unambiguously assign USVs to individual signalers, regardless of inter-mouse distances, are needed to distinguish between these possibilities.