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Many signals found in nature seem exaggerated, for instance in size or colour. According to the receiver bias hypothesis such signal features evolve as a consequence of nonfunctional response biases in receivers. In this study we tested this hypothesis using chickens, Gallus gallus domesticus, in a virtual evolution experiment testing the potentiality of receiver bias to drive the evolution of exaggerated signals. The chickens played the role of receivers that can respond to the preferred stimuli displayed by the sender on a peck-sensitive computer screen. The preferred stimulus was kept and evolved, in the direction specified by the chicken, before being introduced to the next chicken of the successive generation. The chickens were tested on signals changing in three dimensions: length, intensity and area. In all three cases, the signals became considerably exaggerated and beyond what was required for accurate discrimination. Our results support the hypothesis that response biases emerging in discrimination tasks are sufficient to cause the evolution of signal exaggeration. |
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