Sex-dependent modulation of ultrasonic vocalizations in house mice (Mus musculus musculus).

House mice (Mus musculus) emit ultrasonic vocalizations (USVs), which are surprisingly complex and have features of bird song, but their functions are not well understood. Previous studies have reported mixed evidence on whether there are sex differences in USV emission, though vocalization rate or other features may depend upon whether potential receivers are of the same or opposite sex. We recorded the USVs of wild-derived adult house mice (F1 of wild-caught Mus musculus musculus), and we compared the vocalizations of males and females in response to a stimulus mouse of the same- or opposite-sex. To detect and quantify vocalizations, we used an algorithm that automatically detects USVs (Automatic Mouse Ultrasound Detector or A-MUD). We found high individual variation in USV emission rates (4 to 2083 elements/10 min trial) and a skewed distribution, with most mice (60%) emitting few (≤50) elements. We found no differences in the rates of calling between the sexes overall, but mice of both sexes emitted vocalizations at a higher rate and higher frequencies during opposite- compared to same-sex interactions. We also observed a trend toward higher amplitudes by males when presented with a male compared to a female stimulus. Our results suggest that mice modulate the rate and frequency of vocalizations depending upon the sex of potential receivers

Automatic mouse ultrasound detector (A-MUD): A new tool for processing rodent vocalizations

<div><p>House mice <i>(Mus musculus)</i> emit complex ultrasonic vocalizations (USVs) during social and sexual interactions, which have features similar to bird song (i.e., they are composed of several different types of syllables, uttered in succession over time to form a pattern of sequences). Manually processing complex vocalization data is time-consuming and potentially subjective, and therefore, we developed an algorithm that automatically detects mouse ultrasonic vocalizations (<i>Automatic Mouse Ultrasound Detector</i> or A-MUD). A-MUD is a script that runs on STx acoustic software (S_TOOLS-STx version 4.2.2), which is free for scientific use. This algorithm improved the efficiency of processing USV files, as it was 4–12 times faster than manual segmentation, depending upon the size of the file. We evaluated A-MUD error rates using manually segmented sound files as a ‘gold standard’ reference, and compared them to a commercially available program. A-MUD had lower error rates than the commercial software, as it detected significantly more correct positives, and fewer false positives and false negatives. The errors generated by A-MUD were mainly false negatives, rather than false positives. This study is the first to systematically compare error rates for automatic ultrasonic vocalization detection methods, and A-MUD and subsequent versions will be made available for the scientific community.</p></div

Sex-dependent modulation of ultrasonic vocalizations in house mice (<i>Mus musculus musculus</i>)

<div><p>House mice (<i>Mus musculus)</i> emit ultrasonic vocalizations (USVs), which are surprisingly complex and have features of bird song, but their functions are not well understood. Previous studies have reported mixed evidence on whether there are sex differences in USV emission, though vocalization rate or other features may depend upon whether potential receivers are of the same or opposite sex. We recorded the USVs of wild-derived adult house mice (F1 of wild-caught <i>Mus musculus musculus</i>), and we compared the vocalizations of males and females in response to a stimulus mouse of the same- or opposite-sex. To detect and quantify vocalizations, we used an algorithm that automatically detects USVs (<i>Automatic Mouse Ultrasound Detector</i> or <i>A-MUD</i>). We found high individual variation in USV emission rates (4 to 2083 elements/10 min trial) and a skewed distribution, with most mice (60%) emitting few (≤50) elements. We found no differences in the rates of calling between the sexes overall, but mice of both sexes emitted vocalizations at a higher rate and higher frequencies during opposite- compared to same-sex interactions. We also observed a trend toward higher amplitudes by males when presented with a male compared to a female stimulus. Our results suggest that mice modulate the rate and frequency of vocalizations depending upon the sex of potential receivers.</p></div

Number of USV elements emitted when subjects were presented with same- or opposite-sex individuals.

<p>Boxplots of number of elements (logarithmic scale) emitted by the focal mice in the presence of the stimulus mouse (n = 10 per group). The sex of focal animal is depicted in capital letters and sex of the stimulus animal in brackets. The graph shows median ± 95% CI, including the 25th and the 75th percentiles. * = p<0.05. ^o = outlier data point laying outside the whiskers of the boxplot.</p

Evaluation of error rates among automatic USV detection methods (all recordings).

<p>Boxplots showing the percentage of correct positives (a), false positives (b) and false negatives (c) comparing three automatic processing methods: A-MUD (grey) and a commercially available software using ‘whistle tracking’ (white) or ‘single threshold’ (stippled) settings. The graph shows median ± 95% CI, including the 25th and the 75th percentiles. ** = p ≤ 0.01.</p

Histogram showing variation in the vocal behavior (number of calls) among individuals.

<p>Many mice produced few calls (≤50 elements) during the 10 min trials, though some mice were highly vocal (n = 40). The vertical dashed line shows the arbitrary cutoff used to distinguish between the low and high callers.</p

USV parameters and definitions in A-MUD.

<p>USV parameters and definitions in A-MUD.</p

Number of subjects that were high or low callers when presented with individuals of the same- or opposite-sex.

<p>Number of individuals that emitted > 50 elements (‘high callers’: dark gray) and ≤50 elements (‘low callers’: light gray) during 10 min recordings of males (M) and females (F) in the presence of a female (f) or male (m) stimulus (n = 10 per group). The sex of focal animal is depicted in capital letters and sex of the stimulus animal in brackets. * = p<0.05.</p

Evaluation of error rates among automatic USV detection methods (selected recordings).

<p>Boxplots showing the percentage of correct positives (a), false positives (b) and false negatives (c) with three automatic processing methods: A-MUD (grey) and a commercially available software using ‘whistle tracking’ (white) or ‘single threshold’ (stippled) settings. The graph shows median ± 95% CI, including the 25th and the 75th percentiles. * = p ≤ 0.05. ° = outliers.</p