The evolution of colour polymorphism in British winter‐active Lepidoptera in response to search image use by avian predators

Phenotypic polymorphism in cryptic species is widespread. This may evolve in response to search image use by predators exerting negative frequency‐dependent selection on intraspecific colour morphs, “apostatic selection”. Evidence exists to indicate search image formation by predators and apostatic selection operating on wild prey populations, though not to demonstrate search image use directly resulting in apostatic selection. The present study attempted to address this deficiency, using British Lepidoptera active in winter as a model system. It has been proposed that the typically polymorphic wing colouration of these species represents an anti‐search image adaptation against birds. To test (a) for search image driven apostatic selection, dimorphic populations of artificial moth‐like models were established in woodland at varying relative morph frequencies and exposed to predation by natural populations of birds. In addition, to test (b) whether abundance and degree of polymorphism ar...