Male mouse (Mus musculus) ultrasonic vocalizations to female urine: why is heterosexual experience necessary?

Previous research was consistent with the hypothesis that urinary chemosignals from female mice (Mus musculus) serve as a conditioned stimulus (CS) for the elicitation of male ultrasonic courtship vocalizations while some other unknown aspect of the female serves as an unconditioned stimulus (US). According to this hypothesis adult heterosexual experience is necessary for males to pair the urinary CS with the US. Three experiments further examined this hypothesis. Experiment 1 demonstrated that the hypothesized US was not female behavior. Experience with anesthesized males and females was just as effective as experience with awake conspecifics. Experiments 2 and 3, however, question the primacy of the Classical Conditioning hypothesis. In both experiments sexually naive males were allowed contact with either normal females or female surrogates. The female surrogates were neonatally castrated males (Experiment 2) or hypophysectomized females (Experiment 3), both of which appeared to possess the hypothesized US but not the urinary CS on the basis of previous research. While exposure to normal females caused the highest level of vocalization to urine from normal females, exposure to the two classes of female surrogates also resulted in vocalizations to the urine of normal females. Thus under some circumstances, males do not require experience with a normal female to emit ultrasounds to urine from normal females. Factors in addition to Classical Conditioning must be operating to account fully for the role of adult heterosexual experience in causing female urine to come to elicit male courtship vocalization.