Ultrasonic vocalizations by male hamsters: parameters of calling and effects of playbacks on female behaviour

Abstract

Male and female hamsters, Mesocricetus auratus, were observed during prolonged matings. Ultrasonic vocalizations by the male were frequent initially and declined during testing, but were positively associated with the duration of female lordosis. Most calls were uttered while sniffing the female, although early in the test period when most ejaculations were occurring, high rates were also observed during non-contact behaviour such as grooming. Following exposure to the first female, introduction of a novel female stimulated the return of high rates of male calling. In a follow-up experiment, males uttered more ultrasonic calls in the 30-s period following ejaculation than in the preceding 30-s interval. These results provide evidence that males utter ultrasonic vocalizations that enhance lordosis during extended sexual interactions, and that the patterns of male calling are consistent with behaviours that maintain receptivity and ensure successful fertilization. Two other experiments examined whether different male calls have different effects on female behaviour. Males utter at least two structurally distinct types of ultrasonic vocalizations during sexual behaviour: one is produced during interaction with a female in lordosis (during-female), and the second is uttered following removal of the female (post-female). In the first experiment, playbacks of during- and post-female calls were equally effective in prolonging the duration of lordosis in females relative to taped noise. In a second experiment, however, tape-recorded post-female calls induced more ultrasonic vocalizations from females than during-female calls; both call types elicited more calling from females than taped noise. Therefore, although there were differences in potency, during- and post-female calls did not differ in the types of responses elicited from females under two different conditions. Thus, these male calls induce context-appropriate responses in females. In a final eperiment, structural differences were found in the male vocalizations occurring just before and after ejaculation. Together, these experiments show that ultrasonic vocalizations by male hamsters consistently vary in rate and structure during sexual interactions, and suggest that the responses of females may vary accordingly.