The deflection hypothesis: eyespots on the margins of butterfly wings do not influence predation by lizards

Feeding experiments with lizards are used to examine the function of small eyespot markings found along the wing margins of many butterfly species. Such eyespots are frequently suggested to function by deflecting the attacks of vertebrate predators away from the vulnerable body towards the wing margins, which can tear easily; the eyespots are considered to mislead predators and to act as targets for their attacks. Such misdirected attacks give the butterflies a chance to evade capture, albeit sometimes losing pieces of wing tissue. As a model prey species, we used fruit-feeding individuals of the tropical butterfly Bicyclus anynana that were attacked in a standard way in laboratory cages by the anolis lizard, Anolis carolinensis. We also manipulated the butterflies' wing patterns by pasting eyespots on different parts of the wings to examine the deflection hypothesis in more detail. Our results indicate no influence on the lizard attacks either of the presence of eyespots, or of their position on the wings. The lizards attacked butterflies in a highly stereotyped manner both when the prey were presented on matching or on contrasting backgrounds. We thus found no support for the deflection hypothesis for attacks by insectivorous lizards. Indeed, our only support to date has been obtained for naive flycatcher birds, but even this requires further corroboration. Although effective deflection may occur rather infrequently, except perhaps under certain ecological conditions such as high-density feeding of butterflies on fallen fruit, it may still be sufficiently consistent over time to have contributed to shaping the evolution of marginal eyespot patterns. (c) 2007 The Linnean Society of London.