Social costs enforce honesty of a dynamic signal of motivation

Understanding the processes that promote signal reliability may provide important insights into the evolution of diverse signaling strategies among species. The signals that animals use to communicate must comprise mechanisms that prohibit or punish dishonesty, and social costs of dishonesty have been demonstrated for several fixed morphological signals (e.g. color badges of birds and wasps). The costs maintaining the honesty of dynamic signals, which are more flexible and potentially cheatable, are unknown. Using an experimental manipulation of the dynamic visual signals used by male veiled chameleons (Chamaeleo calyptratus) during aggressive interactions, we tested the idea that the honesty of rapid color change signals is maintained by social costs. Our results reveal that social costs are an important mechanism maintaining the honesty of these dynamic color signals − 'dishonest' chameleons whose experimentally manipulated coloration was incongruent with their contest behavior received more physical aggression than 'honest' individuals. This is the first demonstration that the honesty of a dynamic signal of motivation − physiological color change − can be maintained by the social costliness of dishonesty. Behavioral responses of signal receivers, irrespective of any specific detection mechanisms, therefore prevent chameleon cheaters from prospering.