Behavioural Processes 63 (2003) 53–61 Timing of presentation of an audience: aggressive priming and audience effects in male displays of Siamese fighting fish (Betta splendens) Ricardo J. Matos ∗ , Tom M. Peake, Peter K. McGregor Department of Animal Behaviour, Zoological Institute, Copenhagen University, Tagensvej 16, DK-2200 Copenhagen N, Denmark Received 22 July 2002; received in revised form 31 January 2003; accepted 5 February 2003 Abstract Studies of animal communication often underestimate the presence of individuals other than the signaller–receiver dyad. Signalling interactions often occur in the presence of non-participating individuals (audiences); the effect of these individuals upon the dynamics of interactions has been called the audience effect. Recent studies of fighting fish Betta splendens have shown that the presence of a male audience can increase aggression during interactions. However, in many of these studies males were allowed to see the audience prior to the interaction, thus such pre-exposure may have facilitated aggressive behaviour (aggressive priming). Here we present results of two experiments designed to examine the relative importance of priming and audience effects on the dynamics of aggressive interactions. Males that were pre-exposed showed higher levels of aggression during subsequent interactions regardless of the presence or absence of an audience. When only one of the interactants had been pre-exposed to the audience, the non-exposed male showed similar increases in aggressive behaviour, i.e. matching the level of aggression showed by his opponent. Taken together these results suggest that aggressive priming may have resulted in an over-estimation of the audience effect in previous studies. The results still highlight the importance of social environment in determining the dynamics and outcomes of aggressive contests. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Aggressive behaviour; Audience effect; Betta splendens; Communication network; Priming 1. Introduction Most studies of animal communication have as- sumed that individuals exchange signals in social iso- lation. Consequently, models of communication and empirical work have addressed primarily the evolution of signals in a dyadic context. However, an increasing number of studies have considered the influence of the social environment on signalling behaviour (e.g. ∗ Corresponding author. Tel.: +45-35-32-13-46; fax: +45-35-32-12-99. E-mail address: rmatos@zi.ku.dk (R.J. Matos). McGregor and Peake, 2000; McGregor et al., 2000; Johnstone, 2001; Dugatkin, 2001). In these studies the natural environment where communication occurs is considered to be a network of several potential re- ceivers and signallers. The dynamics created by such an environment have marked effects on the costs and benefits of signalling, and thus on the behavioural strategies used by signallers during interactions (e.g. McGregor and Peake, 2000; McGregor et al., 2000; Johnstone, 2001). One of the major costs of signalling in a network environment is imposed by “unwanted” conspecific receivers. For example, in several species the individuals (eavesdroppers or audiences) that 0376-6357/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0376-6357(03)00029-9