Abstract
Ultrasonic vocalizations (USV) of mice are increasingly recognized as informative dependent variables in studies using mouse models of human diseases. While pup vocalizations primarily serve to re-establish contact with the mother, adult male “songs” were considered to be courtship signals. Alternatively, mouse USVs may generally function as territorial signals. To distinguish between these two hypotheses, we compared the structure and usage of adult male and female USVs in staged resident-intruder encounters. If calls function primarily as courtship signals, males should respond stronger than females, specifically when presented with a female intruder. Refuting this hypothesis, we found that in response to female intruders, females called more than males (228±32 calls/min vs. 71±15 calls/min), and males called more to female than to male intruders (14±7.5 calls/min). There were no significant differences in the acoustic characteristics of the calls given by females and males. To control for the influence of the intruder's behavior on calling, we repeated the experiments using anaesthetized intruders. Again, females produced more calls to female than male intruders (173±17 calls/min vs. 71±15 calls/min), while males called more in response to female than male intruders (39±17 calls/min), and there were no acoustic differences in female and male calls. The vocal activity did not differ significantly with regard to intruder state (awake or anaesthetized), while the acoustic structure exhibited significant differences. Taken together, our findings support the view that calls do not mainly function as courtship signals, although they might serve both a territorial (sex-independent) and a courtship function. The comparison of responses to awake vs. anaesthetized intruders suggests that the latter are sufficient to elicit vocal activity. The subtle acoustic differences, however, indicate that the subject differentiates between intruder states.
Highlights
In the last years, mouse ultrasonic vocalizations (USV) have received increasing attention, as behavioral read-outs in genetic mouse models of human psychiatric disorders (e.g., [1,2,3]; reviewed in [4]), and in studies of the genetic foundations of speech [5]
Experiment 1 In response to female intruders, female mice called significantly more than males (t-test, t = 25.1, N = 28, P =,0.001), and overall produced the highest number of calls
In response to female intruders, both females and males revealed a short latency until they began calling (t = 20.1, N = 24, P = 0.909), while the latency was significantly longer in males confronted with male intruders than with female intruders (t = 5.4, N = 20, P =,0.001; Figure 1B)
Summary
Mouse ultrasonic vocalizations (USV) have received increasing attention, as behavioral read-outs in genetic mouse models of human psychiatric disorders (e.g., [1,2,3]; reviewed in [4]), and in studies of the genetic foundations of speech [5]. Mouse pups emit isolation calls when removed from the mother, and in response to dropping body temperature, handling, or specific smells These calls are considered to be signals of need addressed to mothers [6,7,8]. The view that calls may serve a territorial function – that is to repel intruders or facilitate interaction and assessment – is supported by studies that examined female vocal behavior. Recent studies using the resident-intruder paradigm, where a subject in its ‘‘home cage’’ is confronted with an intruding individual, showed that resident females emitted a comparable amount of USVs during these encounters as males [19] In this design, the ‘resident’ animal was kept for one or more days in a ‘home’ cage. Scattoni and colleagues [1,20] found that USVs produced during resident-intruder tests could be used to characterize the social relationships between different females or to establish social dominance hierarchies [18]
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