Ultrasonic vocalizations in house mice depend upon genetic relatedness of mating partners and correlate with subsequent reproductive success

Background
Courtship vocalizations are used by males of many species to attract and influence the behavior of potential mating partners. Our aim here was to investigate the modulation and reproductive consequences of courtship ultrasonic vocalizations (USVs) in wild-derived house mice (Mus musculus musculus). The courtship USVs of male mice are surprisingly complex and are composed of a variety of different syllable types. Our specific aims were to test whether (1) the emission of courtship USVs depends upon the kinship of a potential mating partner, and (2) whether USV emission during courtship affects the pairs’ subsequent reproductive success.

Results
We experimentally presented males with an unfamiliar female that was either genetically related or unrelated, and we recorded USV emission, first while the sexes were separated by a perforated partition and then during direct interactions, after removing the partition. USVs were detected by the Automatic Mouse Ultrasound Detector (A-MUD) and manually classified into 15 syllable types. The mice were kept together to test whether and how courtship vocalizations predict their subsequent reproductive success. We found that the mice significantly increased their amount of vocalizations (vocal performance) and number of syllable types (vocal repertoire) after the partition was removed and they began interacting directly. We show that unrelated pairs emitted longer and more complex USVs compared to related pairs during direct interactions. Unrelated pairs also had a greater reproductive success compared to related pairs, and in addition we found a negative correlation between the mean length and amount of vocalizations with the latency to their first litter.

Conclusion
Our study provides evidence that house mice modulate the emission of courtship USVs depending upon the kinship of potential mating partners, and that courtship USVs correlate with reproductive success.