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

Abstract

House mice adjust their signaling behavior depending on the social context of an interaction, but which aspects of context elicit the strongest responses from these individuals is often difficult to determine. To explore how internal and external contextual factors influence how house mice produce and respond to social signals, we assessed how dominant and subordinate male mice differed in their ultrasonic vocalization (USV) production in response to playback of broadband vocalizations (BBVs, or squeaks) when given limited access to a stimulus female. We used a repeated measures design in which each male was exposed to two types of trials with different odor conditions: either just female odors (Fem condition) or female odors in addition to the odors of potential competitors, other males (Fem+Male condition). The presence of odors from other males in this assay served as a proxy for an "audience" as the male interacted with the stimulus female. These conditions were replicated for 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). By assessing dominance status of the focal individual and familiarity of the "audience", we are able to explore how these factors may affect one another as males respond to BBVs. Dominants and subordinates did not differ in their baseline vocal production (vocalizations produced prior to squeak playback) or response to squeaks. However, all groups, regardless of dominance status or odor condition, reduced their vocal production in response to BBV playback. The presence of unfamiliar male odor prompted mice to decrease their baseline level of calling and decrease the complexity of their vocal repertoire compared to trials that only included female odor, and this effect also did not differ across dominance status. Importantly, the presence of male odor did not affect vocal behavior when the male odor was familiar to the focal individual. 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.

Fig 1. Representative spectrograms of (A) Ultrasonic vocalizations (USVs) and (B) Broadband vocalizations (BBVs).

The circled vocalization in (A) is an example of a 50 kHz harmonic USV.

Fig 2. Experimental assay and design.

(A) Split-cage paradigm used to evaluate the effects of only BBV playback on male vocal behavior, modified to create the Fem+Male condition for this study. Male and female symbols present on the male mouse’s side of the cage represent the presence of dirty bedding from male and female mice. (B) Experimental groups broken up by familiarity cohort, dominance status, and odor condition. A question mark icon is used to illustrate unfamiliarity with the odor stimulus in the trial, and an exclamation point icon is used to illustrate familiarity with the odor stimulus in the trial.

Fig 3. Properties of vocal repertoires.

(A) Baseline USVs produced in the Fem condition vs the Fem+Male condition. (B) Duration of baseline USVs in seconds. (C) Baseline proportion of harmonic USVs (# baseline harmonics/# baseline USVs). Proportion of baseline harmonic USVs was calculated as baseline harmonic USVs /(baseline harmonic USVs + baseline nonharmonic USVs). Blues represent the unfamiliar odor cohort, reds represent the familiar odor cohort. Bars represent the means of the experimental groups, and means from dominants and subordinates are pooled due to the lack of effect of social status. Error bars are calculated from standard errors. Individual points of data noted with dominants as X’s and subordinates as circles.

Fig 4. Number of USVs produced across test periods (A) in the unfamiliar odor cohort, and (B) in the familiar odor cohort.

Average USV production of dominants is represented by the solid lines, and average USV production of subordinates is represented by dashed lines. Lighter lines denote average USV production of individuals in the Fem condition, while darker lines denote average USV production of individuals in the Fem+Male condition. Error bars are calculated from standard errors.

Fig 5. Proportion of harmonic USVs across test period out of total USVs (A) in the unfamiliar odor cohort and (B) in the familiar odor cohort.

Average harmonic USV production of dominants is represented by the solid lines, and average harmonic USV production of subordinates is represented by dashed lines. Lighter lines denote average harmonic USV production of individuals in the Fem condition, while darker lines denote average harmonic USV production of individuals in the Fem+Male condition. Proportion of harmonic USVs for each test period was calculated as harmonic USVs in test period/(harmonic USVs + nonharmonic USVs in test period). The significance bar in 5A) showing increased usage of proportion of harmonic USVs in the recovery period compared to the baseline and playback period is dark blue, representing that it only applies to the Fem+Male conditions, not the Fem conditions. Error bars are calculated from standard errors.

Fig 6. Duration of time the focal male (A and C) or the stimulus female (B and D) spent investigating the divider window across test periods in the unfamiliar odor cohort (A and B) and in the familiar odor cohort (C and D).

Average duration of investigation in trials with dominant males is represented by the solid lines, and average duration of investigation in trials with subordinates is represented by dashed lines. Lighter lines denote average investigation during trials in the Fem condition, while darker lines denote average investigation in the Fem+Male condition. Error bars are calculated from standard errors.