Presence of a potential competitor and its individual identity modulate ultrasonic vocalizations in male hamsters

Animal communication takes place in a complex environment that is constantly modulated by particular social conditions. The majority of examples of signalling behaviours modulated by social context involve the presence of an individual of a particular sex or one that simply represents general competition. However, the identity of the individuals and the social relationships among individuals could also significantly modulate acoustic behaviour. In this study, I examined whether the presence of another male competitor modulates the post-interaction vocal response of a male subject to an oestrous female stimulus in golden hamsters, Mesocricetus auratus. I found that the presence of a potential competitor during an interaction with a female across a wire-mesh barrier significantly decreased the duration, tempo and energy of ‘post-female calls’ over time (experiment 1). Moreover, the call duration and energy of one-note simple calls changed over time depending on the identity of the stimulus male. Males that experienced social conflict and lost a fight maintained call duration and increased the energy of their calls over time, but only if the social interaction with the female was in the presence of another familiar neutral male and not in the presence of a familiar winner male (experiment 2). When the winner male stimulus was present, the duration and energy of the calls produced by the loser decreased with time. Individual recognition between familiar conspecifics with different shared experiences likely modulated the motivational state of the male subject and his vocal response after a social interaction with the female. This study provides new evidence that social complexity (competition and individual recognition) can induce dynamic changes of spectrotemporal features of hamster sexual ultrasonic vocalizations.