What matters to a mouse? Effects of internal and external context on male vocal response to female squeaks

Individuals plastically adjust their signaling behavior depending on the social context of an interaction, but which aspects of context elicit the strongest responses from individuals is often difficult to determine. To explore how internal and external contextual factors influence the communication of house mice, we employed a split-cage playback assay to assess how dominant and subordinate male mice differed in their ultrasonic vocalization (USV) production in response to playback of broadband vocalizations (BBVs, or squeaks). We assessed how individuals altered their behavior depending on the odors present during the assay: either just female odors (Fem condition) or female odors in addition to the odors of potential competitors, other males (Fem+Male condition). Using this repeated-measures design, we evaluated two distinct cohorts of individuals: males exposed to the odor of familiar competitors in the Fem+Male condition (Familiar odor cohort), and males exposed to the odor of unfamiliar competitors in the Fem+Male condition (Unfamiliar odor cohort). While dominants and subordinates did not differ in their baseline vocal production or response to squeaks, all groups reduced their vocal production in response to BBV playback, and the addition of unfamiliar male odor prompted mice to decrease their baseline levels of calling and decrease the complexity of their vocal repertoire. Importantly, this effect of additional male odor was not present when individuals were presented with male odor familiar to them. These findings suggest that mice alter their vocal behavior during courtship interactions in response to cues that indicate the presence of potential competitors, and this response is modulated by the familiarity of these competitor cues.