The effect of an audience on intrasexual communication in male Siamese fighting fish, Betta splendens

The evolution of signals has mainly been considered in the context of an emitter-receiver dyadic interaction. However, communication usually occurs in the presence of individuals (an audience) that are not directly involved in the communication interaction, and it is more realistic to assume that signal evolution occurs in a network. Several types of information could be available to an audience, and, therefore, the presence of an audience could have effects on the behavior of the communicating animals and on signal evolution. We investigated whether the presence of an audience of conspecifics affected intrasexual aggressive communication in male fighting fish. We found that if the audience was a female, males increased the intensity of conspicuous displays that can be used in communication with both males and females and decreased highly aggressive displays that are solely directed to males. If the audience was a male of similar size, there was no significant change in the way in which males displayed. These results suggest that the presence of an audience could be one reason that many long-range and conspicuous signals are often shaped to transmit information to both males and females.