THE COST OF THREAT DISPLAYS AND THE STABILITY OF DECEPTIVE COMMUNICATION

Several analyses of intraspecific animal communication have suggested that threat displays must convey reliable information about the abilit ies of the signaller in order to be evolutionarily stable. In this pap er, a game-theoretic model shows that bluffing by animals of low fight ing ability can persist as a profitable tactic in a stable communicati on system. It is assumed that use of the threat display depends upon v ariation in fighting ability that is not visible to the opponent and t hat there is a fitness cost, or ''handicap'', paid by animals that thr eaten and subsequently lose. Analysis of the model shows that a handic ap is necessary for stable communication and that the effectiveness of the threat increases with the magnitude of the handicap. However, the handicap does not ensure fully reliable communication and bluffing al ways forms part of the evolutionarily stable strategy (ESS). At the ES S, the very strongest and the very weakest members of the population t hreaten, while animals of intermediate strength do not. This is possib le because, although weaker animals are liable to greater handicaps wh en they signal, they also gain greater benefits than strong animals us ing the same display. If all animals that threaten pay the handicap re gardless of the outcome of the fight, then there is no ESS. These resu lts provide a possible explanation for bluffing by the stomatopod crus tacean, Gonodactylus bredini, a species in which animals weakened by m olting successfully repulse stronger opponents by use of threat displa ys. (C) 1995 Academic Press Limited