Whistle while you work it : the role of energetic state and audience identity in singing mouse vocal effort



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Elaborate animal displays serve crucial functions as animals attempt to deploy displays precisely to maximize reproductive rewards and minimize potential costs. These costs include both the potential wasted resources from a failed display and the possibility that a display might evoke attack from a rival or predator. To achieve this, individuals must integrate both internal and external information before deciding whether to signal and how much energy to invest into a given signal. Here we examine display effort in Alston’s singing mouse, Scotinomys teguina. using leptin, a hormone secreted by adipose tissue that regulates energy allocation. We manipulated individual perception of energy balance through intraperitoneal injection of exogenous leptin and social context through playback of conspecific song. Leptin-injected mice responded with song to playback more frequently and quickly than saline-injected controls. Although leptin promoted increased song effort, we found that leptin also reduced song duration. Playback of conspecific songs also increased song effort. We next focused on social context by recording focal males when alone, in the presence of a familiar female mouse, with an unfamiliar female mouse, and with an unfamiliar male mouse. Singing mice produce two distinctive types of songs: the long, well-studied advertisement song and a short “strophe” song that is disproportionately produced in the presence of females. Advertisement songs produced in the presence of females are quieter but longer than those produced in other treatments. These advertisement songs also contain enough information to identify individuals. Upon further analysis of recordings, we find that singing mice also produce short vocalizations that are similar to the ultrasonic vocalizations common in rodents. These are almost never found when alone and are vastly more common in female-directed treatments than in other treatments. A cluster analysis shows that they fall into four distinct types: peeps, sweeps, and warbles, plus the short “strophe” songs discussed previously. All are more commonly produced to female audiences than to other males, and all contain identity information similarly to advertisement songs.


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