Communication at the Garden Fence – Context Dependent Vocalization in Female House Mice

<div><p>House mice (<i>Mus musculus</i>) live in social groups where they frequently interact with conspecifics, thus communication (<i>e</i>.<i>g</i>. chemical and/or auditory) is essential. It is commonly known that male and female mice produce complex vocalizations in the ultrasonic range (USV) that remind of high-pitched birdsong (so called mouse song) which is mainly used in social interactions. Earlier studies suggest that mice use their USVs for mate attraction and mate choice, but they could also be used as signal during hierarchy establishment and familiarization, or other communication purposes. In this study we elucidated the vocalization behaviour of interacting female mice over an extended period of time under semi-natural conditions. We asked, if the rate or structure of female vocalization differs between different social and non-social contexts. We found that female USV is mainly used in social contexts, driven by direct communication to an unknown individual, the rate of which is decreased over time by a familiarization process. In addition we could show that female mice use two distinct types of USVs, differing in their frequency, which they use differently depending on whether they directly or indirectly communicate with another female. This supports the notion that vocalization in mice is context dependent, driven by a reasonable and yet underestimated amount of complexity that also involves the interplay between different sensory signals, like chemical and auditory cues.</p></div

The experimental set-up.

<p>a) Photo of the arena set-up with one animal at the contact window (red circle). b) The contact window when closed and c) the open contact window. d) Schematic view of the arena with context regions as used for video scoring. The standard equipment for the experiments is colored in grey, the context regions that were used for video scoring are marked in different colors and inscribed with following abbreviations: CC = contact corners (dark blue); CR = contact region (light blue); CW = contact window (turquoise); F = food; FR = food region (green); H = red Plexiglas house; M = microphone, hanging from the top (see a); MB = male bedding (red); NR = neutral region (yellow); W = water.</p

Spectrograms of the 13 syllable types.

<p>Spectrograms were generated with 256(FFT) using the software Selena (Department of Animal Physiology, University of Tübingen; Germany). For abbreviations see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0097244#pone-0097244-t002" target="_blank">table 2</a>.</p

Songs and syllables in the different recording nights.

<p>a) The number of songs per night for each individual pair of females from sets A and B, as well as the mean number of songs per night in sets A and B. b) The mean number of songs in the different context regions in the four recording nights. c) The first two linear discriminant functions (LD) of syllable parameters in different recording nights. Ellipses show the 95% confidence interval around the group means. The contribution of the two linear discriminants is given below the axis. Arrows indicate the direction of the most influencing parameters on the separation of the data; for the loadings of these and the other syllable parameters see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0152255#pone.0152255.t003" target="_blank">Table 3a</a>.</p

Song duration (a) and syllables rate (b) in the different social contexts.

<p>Box plots are separated by sex and population. Abbreviations and colours as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0097244#pone-0097244-g004" target="_blank">Figure 4</a>. Asterisks denote the cases where found differences were significant (p≤0.05 (*), p≤0.01 (**)).</p

Analysis of qualitative parameters, separated by social context.

(1)<p>DiffPop  =  Different population, different sex; DiffSex  =  Same population, different sex; SameSex  =  Same population, same sex. FRA  =  French, GER  =  German, f  =  female, m  =  male.</p>(2)<p>Calculated as change of frequency over time (kHz/ms).</p>(3)<p>Centre of gravity, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0097244#s2" target="_blank">Methods</a> section <i>Sound analysis</i> for calculation.</p>(4)<p>Post-hoc Wilcoxon rank-sum tests; corrected p-values.</p

Comparison of the repeat number distribution of syllable types.

<p>Presented are graphs for the syllable types (a) JED (Jump-early-down, for details see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0097244#pone-0097244-t002" target="_blank">Table 2</a>) and (b) SDN (Simple-down), with separate graphs for each group (FRA = French, GER = German, f = female, m = male). The solid black lines show the distribution of repeat numbers in the observed syllable sequences (orig). The dotted green and dashed yellow lines show the distribution of repeat numbers in the syllable sequences calculated with the Probability model (PM) and with the Markov model (MM) respectively.</p

Frequency-distribution of the Center of Gravity of syllable frequency.

<p>Data for night 1 (without direct contact) are shown in the upper panel, data for nights 2–4 (with direct contact) in the lower panel. The vertical line is drawn at 45 kHz and separates low-frequency and high-frequency syllables.</p

Scheme of the USV recording box.

<p>The box is made from grey PVC (side and back walls) and non-reflecting glass (front window). Four equal compartments are equipped with bedding, food and water, and acoustically monitored via an ultrasound microphone from above. The partner compartments (compartment pairs at the left and right) are connected via a little window made from metal grid (indicated in white) to allow sensory contact between recording partners (drawing not to scale.)</p

Distribution of doublets (a) and triplets (b) of syllable types.

<p>Doublets and triplets are sorted according to decreasing probability in the real data. Separate graphs for each group (FRA = French, GER = German, f = female, m = male). The solid black lines show the distribution doublets and triplets in the observed syllable sequences (orig). The dotted green and dashed yellow lines show the distribution of the respective doublets and triplets in the syllable sequences calculated with the Probability model (PM) and the Markov model (MM) respectively.</p