Primed to vocalize: Wild-derived male house mice increase vocalization rate and diversity after a previous encounter with a female

Abstract

Males in a wide variety of taxa, including insects, birds and mammals, produce vocalizations to attract females. Male house mice emit ultrasonic vocalizations (USVs), especially during courtship and mating, which are surprising complex. It is often suggested that male mice vocalize at higher rates after interacting with a female, but the evidence is mixed depending upon the strain of mice. We conducted a study with wild-derived house mice (Mus musculus musculus) to test whether male courtship vocalizations (i.e., vocalizations emitted in a sexual context) are influenced by a prior direct interaction with a female, and if so, determine how long the effect lasts. We allowed sexually naïve males to directly interact with a female for five minutes (sexual priming), and then we recorded males’vocalizations either 1, 10, 20, or 30 days later when presented with an unfamiliar female (separated by a perforated partition) and female scent. We automatically detected USVs and processed recordings using the Automatic Mouse Ultrasound Detector (A-MUD version 3.2), and we describe our improved version of this tool and tests of its performance. We measured vocalization rate and spectro-temporal features and we manually classified USVs into 15 types to investigate priming effects on vocal repertoire diversity and composition. After sexual priming, males emitted nearly three times as many USVs, they had a larger repertoire diversity, and their vocalizations had different spectro-temporal features (USV length, slope and variability in USV frequency) compared to unprimed controls. Unprimed control males had the most distinctive repertoire composition compared to the primed groups. Most of the effects were found when comparing unprimed to all primed males (treatment models), irrespective of the time since priming. Timepoint models showed that USV length increased 1 day after priming, that repertoire diversity increased 1 and 20 days after priming, and that the variability of USV frequencies was lower 20 and 30 days after priming. Our results show that wild-derived male mice increased the number and diversity of courtship vocalizations if they previously interacted with a female. Thus, the USVs of house mice are not only context-dependent, they depend upon previous social experience and perhaps the contexts of these experiences. The effect of sexual priming on male courtship vocalizations is likely mediated by neuro-endocrine-mechanisms, which may function to advertise males’ sexual arousal and facilitate social recognition.

Capturing the songs of mice with an improved detection and classification method for ultrasonic vocalizations (BootSnap)

“…We report the performance of the proposed classifier in Sections 3.2 and 3.3 over the DEV_test dataset. The DEV dataset (Zala et al, 2020;Zala et al, 2017a) combined two pre-existing datasets: the first dataset was from 11 wild-derived male and 3 female mice (Mus musculus musculus) recorded for 10 min in the presence of an unfamiliar female stimulus (Zala et al, 2017b). In the second data set, 30 wild-derived male mice (M. musculus musculus) were recorded for 10 min in the presence of an unfamiliar female on 2 consecutive days, first sexually unprimed and then sexually primed (Zala et al, unpublished data).…”

“…After automatically detecting all elements, the DEV dataset was manually classified into 12 classes (Figure 2), depending on the USVs' spectro-temporal features (Hanson et al, 2012;Musolf et al, 2015;Nicolakis et al, 2020;Scattoni et al, 2008;Zala et al, 2020) (Table 2 in Supplementary materials). These classes are based on frequency changes (Zala et al, 2020) (> 5 kHz increase "up", > 5 kHz decrease "d"), on the number of components (corresponding to breaks in the frequency track; "c2" with 2 and "c3" with 3 components), on changes of frequency direction (≥ 2 changes "c") or shape (u-shape, "u", u-inverted shape, "ui"), on frequency modulation (< 5kHz, "f"), on time (5-10 ms, "s", < 5ms, "us"), and harmonic elements, "h". It is worth noting that there are 2 more USV classes, USVs with 4 "c4" and 5 "c5" components.…”

“…Our ground truth (or 'gold standard') was based on manual classification, and we used two independent observers to classify USVs and to evaluate our ground truth, we evaluated inter-observer reliability (IOR). The first 100 USVs of 10 sound files were manually classified into 15 USV types by two of the authors, and both have much experience (Nicolakis et al (2020), Marconi et al (2020), and Zala et al (2020)). We used five arbitrarily selected sound files from the DEV dataset and all five sound files used for the EV dataset (EV_wild and EV_lab).…”

“…This procedure allowed us to monitor changes in vocalizations as courtship progressed over time, and the mice also obtained socio-sexual contact and experience through indirect and direct interactions. We recently found that mice significantly increased the amount of USVs (vocal performance) and the number of syllable types (vocal repertoire) after sexual priming (Zala et al (2020)) and after the partition was removed and they began interacting directly (Nicolakis et al, 2020). For the second dataset of this study, we only used recordings during the first 10 min (with the divider) on both days (before and after sexual experience).…”

“…They concluded that the latter method is superior in terms of TPR and FPR. Zala et al (2020) have since provided an updated version of A-MUD, which overcomes previous difficulties in identifying faint and short USVs.…”