Fearful symmetry: pattern size and asymmetry affects aposematic signal efficacy

Aposematic animals use anti-predator defence mechanisms such as distasteful ness coupled with distinctive odours, sounds, or colour patterns to signal their unprofitability to potential predators. By subjecting artificial 'but terflies' with different visual signals to predation from domestic chicks w e show that the protective value of such visual warning displays is enhance d by increasing size of the signal pattern elements and decreased by patter n asymmetry. These results provide the first experimental evidence that pre dation may select for individual symmetry of visual warning displays, and c oncur with earlier demonstrations that asymmetric signals are more difficul t to detect, learn, and remember, compared to symmetric signals. Collective ly, our findings suggest that prey species possessing warning coloration sh ould be subjected to selection for large and symmetric pattern elements.