Use of behavioural stochastic resonance by paddle fish for feeding

Stochastic resonance is the phenomenon whereby the addition of an optimal l evel of noise to a weak information-carrying input to certain nonlinear sys tems can enhance the information content at their outputs(1-4). Computer an alysis of spike trains has been needed to reveal stochastic resonance in th e responses of sensory receptors(5-7) except for one study on human psychop hysics(8). But is an animal aware of, and can it make use of, the enhanced sensory information from stochastic resonance? Here, we show that stochasti c resonance enhances the normal feeding behaviour of paddlefish (Polyodon s pathula)(9,10), which use passive electroreceptors(11,12) to detect electri cal signals from planktonic prey(13). We demonstrate significant broadening of the spatial range for the detection of plankton when a noisy electric f ield of optimal amplitude is applied in the water. We also show that swarms of Daphnia plankton are a natural source of electrical noise. Our demonstr ation of stochastic resonance at the level of a vital animal behaviour, fee ding, which has probably evolved for functional success, provides evidence that stochastic resonance in sensory nervous systems is an evolutionary ada ptation(14).