Automated behavioral analysis reveals that mice employ a bait-and-switch escape mechanism to de-escalate social conflict.

Intraspecies aggression has profound ecological and evolutionary consequences, as recipients can suffer injuries, decreases in fitness, and become outcasts from social groups. Although animals implement diverse strategies to avoid hostile confrontations, the extent to which social influences affect escape tactics is unclear. Here, we used computational and machine-learning approaches to analyze complex behavioral interactions as mixed-sex groups of mice, Mus musculus, freely interacted. Mice displayed a rich repertoire of behaviors marked by changes in behavioral state, aggressive encounters, and mixed-sex interactions. A prominent behavioral sequence consistently occurred after aggressive encounters, where males in submissive states quickly approached and transiently interacted with females immediately before the aggressor engaged with the same female. The behavioral sequences were also associated with substantially fewer physical altercations. Furthermore, the male's behavioral state and the interacting partners could be predicted by distinct features of the behavioral sequence, such as kinematics and the latency to and duration of male-female interactions. More broadly, our work revealed an ethologically relevant escape strategy influenced by the presence of females that may serve as a mechanism for de-escalating social conflict and preventing consequential reductions in fitness.

Mouse vocal emission and acoustic complexity do not scale linearly with the size of a social group.

Adult mice emit ultrasonic vocalizations (USVs), sounds above the range of human hearing, during social encounters. While mice alter their vocal emissions between isolated and social contexts, technological impediments have hampered our ability to assess how individual mice vocalize in group social settings. We overcame this challenge by implementing an 8-channel microphone array system, allowing us to determine which mouse emitted individual vocalizations across multiple social contexts. This technology, in conjunction with a new approach for extracting and categorizing a complex, full repertoire of vocalizations, facilitated our ability to directly compare how mice modulate their vocal emissions between isolated, dyadic and group social environments. When comparing vocal emission during isolated and social settings, we found that socializing male mice increase the proportion of vocalizations with turning points in frequency modulation and instantaneous jumps in frequency. Moreover, males change the types of vocalizations emitted between social and isolated contexts. In contrast, there was no difference in male vocal emission between dyadic and group social contexts. Female vocal emission, while predominantly absent in isolation, was also similar during dyadic and group interactions. In particular, there were no differences in the proportion of vocalizations with frequency jumps or turning points. Taken together, the findings lay the groundwork necessary for elucidating the stimuli underlying specific features of vocal emission in mice.

Maturation of Social-Vocal Communication in Prairie Vole (Microtus ochrogaster) Pups.

Impairments in social communication are common among neurodevelopmental disorders. While traditional animal models have advanced our understanding of the physiological and pathological development of social behavior, they do not recapitulate some aspects where social communication is essential, such as biparental care and the ability to form long-lasting social bonds. Prairie voles (Microtus ochrogaster) have emerged as a valuable rodent model in social neuroscience because they naturally display these behaviors. Nonetheless, the role of vocalizations in prairie vole social communication remains unclear. Here, we studied the ontogeny [from postnatal days (P) 8-16] of prairie vole pup ultrasonic vocalizations (USVs), both when isolated and when the mother was present but physically unattainable. In contrast to other similarly sized rodents such as mice, prairie vole pups of all ages produced isolation USVs with a relatively low fundamental frequency between 22 and 50 kHz, often with strong harmonic structure. Males consistently emitted vocalizations with a lower frequency than females. With age, pups vocalized less, and the acoustic features of vocalizations (e.g., duration and bandwidth) became more stereotyped. Manipulating an isolated pup's social environment by introducing its mother significantly increased vocal production at older (P12-16) but not younger ages, when pups were likely unable to hear or see her. Our data provide the first indication of a maturation in social context-dependent vocal emission, which may facilitate more active acoustic communication. These results help lay a foundation for the use of prairie voles as a model organism to probe the role of early life experience in the development of social-vocal communication.

Ultrasonic signals associated with different types of social behavior of mice.

Communication plays an integral role in human social dynamics and is impaired in several neurodevelopmental disorders. Mice are used to study the neurobiology of social behavior; however, the extent to which mouse vocalizations influence social dynamics has remained elusive because it is difficult to identify the vocalizing animal among mice involved in a group interaction. By tracking the ultrasonic vocal behavior of individual mice and using an algorithm developed to group phonically similar signals, we showed that distinct patterns of vocalization emerge as male mice perform specific social actions. Mice dominating other mice were more likely to emit different vocal signals than mice avoiding social interactions. Furthermore, we showed that the patterns of vocal expression influence the behavior of the socially engaged partner but do not influence the behavior of other animals in the cage. These findings clarify the function of mouse communication by revealing a communicative ultrasonic signaling repertoire.

Sex differences in vocal communication of freely interacting adult mice depend upon behavioral context.

Ultrasonic vocalizations (USVs) are believed to play a critical role in mouse communication. Although mice produce USVs in multiple contexts, signals emitted in reproductive contexts are typically attributed solely to the male mouse. Only recently has evidence emerged showing that female mice are also vocally active during mixed-sex interactions. Therefore, this study aimed to systematically quantify and compare vocalizations emitted by female and male mice as the animals freely interacted. Using an eight-channel microphone array to determine which mouse emitted specific vocalizations during unrestrained social interaction, we recorded 13 mixed-sex pairs of mice. We report here that females vocalized significantly less often than males during dyadic interactions, with females accounting for approximately one sixth of all emitted signals. Moreover, the acoustic features of female and male signals differed. We found that the bandwidths (i.e., the range of frequencies that a signal spanned) of female-emitted signals were smaller than signals produced by males. When examining how the frequency of each signal changed over time, the slopes of male-emitted signals decreased more rapidly than female signals. Further, we revealed notable differences between male and female vocal signals when the animals were performing the same behaviors. Our study provides evidence that a female mouse does in fact vocalize during interactions with a male and that the acoustic features of female and male vocalizations differ during specific behavioral contexts.

High channel count microphone array accurately and precisely localizes ultrasonic signals from freely-moving mice.

BACKGROUND: An integral component in the assessment of vocal behavior in groups of freely interacting animals is the ability to determine which animal is producing each vocal signal. This process is facilitated by using microphone arrays with multiple channels. NEW METHOD AND COMPARISON WITH EXISTING METHODS: Here, we made important refinements to a state-of-the-art microphone array based system used to localize vocal signals produced by freely interacting laboratory mice. Key changes to the system included increasing the number of microphones as well as refining the methodology for localizing and assigning vocal signals to individual mice. RESULTS: We systematically demonstrate that the improvements in the methodology for localizing mouse vocal signals led to an increase in the number of signals detected as well as the number of signals accurately assigned to an animal. CONCLUSIONS: These changes facilitated the acquisition of larger and more comprehensive data sets that better represent the vocal activity within an experiment. Furthermore, this system will allow more thorough analyses of the role that vocal signals play in social communication. We expect that such advances will broaden our understanding of social communication deficits in mouse models of neurological disorders.