Adaptive functions of ultrasonic vocalizations in male mice

During courtship and mating male house mice (Mus musculus) emit ultrasonic vocalizations (USVs), which are surprisingly complex and contain features of bird song (i.e., strings of syllables, often different types, uttered in succession to form a recognizable sequence over time). The discovery that male mice produce silent songs has spurred much interest in this behavior, and USVs are rapidly becoming an important model for vocalization research and a common behavioral phenotype for a wide variety of studies using mouse models. The adaptive functions of the USVs of house mice are still unclear, however, as most studies have only investigated domesticated laboratory strains. We conducted the first studies on the USVs of wild house mouse, and we found that females are attracted to male USVs and they prefer the calls of non-siblings versus siblings. We conducted spectral analyses and found that males USVs are individually distinctive and show more differences between non-siblings than siblings. Thus, female mice potentially use male USVs for individual recognition and for assessing kinship of potential mates. Our general aim is to determine the adaptive functions of male USVs, and more specifically, we will test whether and how USVs affect males reproductive success through mate choice, male-male competition, or both. We will test whether USVs provide reliable indicators of males social status, health, or genetic quality or compatibility. Furthermore, we will test whether females are better able to recognize individual males or assess their quality when they are able to inspect both USVs and olfactory cues (multimodal signals). We will study wild mice in seminatural population enclosures, as well as the laboratory, which will be the first studies on the USVs of house mice in naturalistic social conditions and the first to test whether USVs provide indicators of phenotypic or genetic quality. Our results will have implications for sexual selection and animal communication, and applied efforts to determine whether vocalizations provide a non- invasive trait for diagnosing disease, genetic speech defects, and animal welfare.

Around 15 years ago, it was discovered that male laboratory mice emit complex ultrasonic vocalizations (USVs) during courtship and mating. Their vocalizations have features of bird song, although we cannot perceive them, as they are beyond the range of human hearing. As ethologists, we aim to understand what kind of information these vocalizations transmit, and how they influence the behavior of potential mates. The aim of our project was to investigate the functions of USVs in wild house mice. More specifically, we aimed to determine whether male courtship USVs enhance their mating success, and what kind of information females obtain from a male's call. We developed new methods for automatically detecting and classifying USVs, which will greatly facilitate research on the acoustic communication of mice. We found that mice of both sexes called at higher rates and higher frequencies during opposite-sex interactions compared to same-sex interactions. The number and diversity of courtship vocalizations that males emitted depended on whether they were previously sexual stimulated (by exposure to receptive females) or not, suggesting that males' calls advertise their sexual arousal to potential mates. After we assigned males to mate with either a related or unrelated female, we found that males emitted longer and more complex USVs when their potential mates were genetically unrelated. Moreover, males that produced more and longer courtship USVs had higher reproductive success than other males. We found that female mice are more attracted to recorded playbacks of USVs of males from the same species (species recognition), and that male USVs contain characteristic features (vocal signatures) that should make it possible to utilize for individual recognition. We have many recordings of USVs that we are still analyzing, and this work will proceed much faster by using our new tools for processing USV data. Our findings will have implications for efforts to develop biometric technology for individual voice identification, and for neuroscience research on acoustic communication. Finally, our findings are relevant for studies using USVs of mice as a model system for studying acoustic communication and the genetic basis of autism and speech disorders in humans.