Batesian mimicry without distastefulness?

Abstract

MANY distasteful species are conspicuously coloured¹ and this is believed to aid their survival through the formation of ‘avoidance images’² by predators. It has been suggested that ‘an efficient escape mechanism’ either provided by a jumping response^3,4, or a fast escape flight^5–7, could be as powerful as distastefulness in influencing a predator's strategy of prey selection, or could in some instances help to increase the relative frequency of an agile mimic of a distasteful but sluggish model⁸. Lindroth³ has made observations on several genera of flea-beetles (Alticinae, Chrysomelidae) and has found great external similarities between them and ground beetles of the genus Lebia (Carabidae), the larva of which is an ectoparasite of the flea-beetle's pupa. He suggests that the flea-beetle, which can escape suddenly from its exposed position on the food-plant by jumping, acts as a model and Lebia as a relatively sluggish mimic. As a parasite, Lebia is found in fewer numbers than the host, a situation also expected of some mimics in relation to their models. Neither was found to be distasteful to bird predators³. Thompson⁴ makes use of Lindroth's³ hypothesis in explaining the occurrence of an apparently aposematic form in females of the nonmimetic common meadow spittlebug, Philaenus spumarius, which is acceptable to predators but for the possession of an efficient close-quarter escape mechanism. Thompson proposes that this mechanism accounts for aposematic morph P. spumarius marginella occurring at a frequency in the population above that maintainable through apostatic selection. In both cases it is proposed that a learning predator comes to associate a particular colour pattern with wasted effort and spurns all forms with a similar appearance.