Consequences of hyper-aggressiveness in Siamese fighting fish: cheaters seldom prospered

Abstract

Zahavi's handicap theory, formalized by Grafen, suggests that ‘cheaters’ must be at a disadvantage if a communication system such as ritualized aggression is to evolve (Grafen 1991, In:Behavioural Ecology: An Evolutionary Approach(Ed. by J. R. Krebs & N. B. Davies), pp. 5–31. Oxford: Blackwell Scientific). To determine whether cheating is disadvantageous inBetta splendens, we held a series of live interactions, after inducing hyper-aggression by socially isolating and then briefly ‘priming’ the fish. Primed isolates, which were no stronger than their rivals, ‘cheated’ by escalating rapidly to tailbeating and biting. These cheaters, however, usually lost fights to non-isolated opponents. Unprimed isolates, i.e. socially isolated fish that were not primed, were not initially hyper-aggressive and thus did not cheat. They lost fewer fights than the cheaters. Results suggested that cheaters lost because they exhausted themselves by their hyper-aggressiveness, allowing their non-hyper-aggressive opponents to win. This result is consistent with the Zahavi–Grafen model of how an ‘honest’ level of ritualized aggression can be stabilized in a population.