Abstract
Animals communicate by exchanging signals frequently in the proximity of other conspecifics that may detect and intercept signals not directed to them. There is evidence that the presence of these bystanders modulates the signaling behavior of interacting individuals, a phenomenon that has been named audience effect. Research on the audience effect has predominantly focused on its function rather than on its proximate mechanisms. Here, we have investigated the physiological and neuromolecular correlates of the audience effect in a cichlid fish (Mozambique tilapia, Oreochromis mossambicus). A male was exposed to a territorial intrusion in the presence or absence of a female audience. Results showed that the presence of the female audience increased territorial defense, but elicited a lower androgen and cortisol response to the territorial intrusion. Furthermore, analysis of the expression of immediate early genes, used as markers of neuronal activity, in brain areas belonging to the social decision-making network (SDMN) revealed different patterns of network activity and connectivity across the different social contexts (i.e., audience × intrusion). Overall, these results suggest that socially driven plasticity in the expression of territorial behavior is accommodated in the central nervous system by rapid changes in functional connectivity between nodes of relevant networks (SDMN) rather than by localized changes of activity in specific brain nuclei.
Highlights
Group living animals establish communication networks in which individuals are within the signaling and receiving range of each other (McGregor, 2005)
There was a main effect of the presence of the audience both on T levels [higher when the audience was absent; F(1, 40) = 15.806, p < 0.001], and on F levels [higher when the audience was present; F(1, 42) = 6.324, p = 0.016], whereas no main effect of the audience was detected on KT levels [F(1, 40) < 0.001, p = 979; Figure 3].There was a main effect of the territorial intrusion both on KT and F levels [lower with territorial intrusion, in both cases; KT: F(1, 40) = 5.031, p = 0.030; F: F(1, 42) = 5.697, p = 0.022], while it had no main effect on T levels[F(1, 40) = 3.344, p = 0.075; Figure 3]
The presence of a female audience modulated the aggressive behavior of the focal males, by increasing the frequency of bite attacks toward territorial intruders
Summary
Group living animals establish communication networks in which individuals are within the signaling and receiving range of each other (McGregor, 2005) In such networks, social information may be broadcasted beyond the sender-receiver dyads toward unintended receivers. It has been predicted that both senders and receivers may have co-evolved adaptations to take advantage of the social information available in communication networks, namely the evolution of eavesdropping in receivers and of changes in signaling behavior in senders in response to the presence of unintended receivers (aka audience effect; McGregor and Peake, 2000). The exposure to an audience before a fight has been shown to prime the focal individual, which increases the expression of aggressive behavior toward its opponent reducing the time necessary to solve the agonistic interaction (Cruz and Oliveira, 2015)
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