The evolution of crypsis when pigmentation is physiologically costly

Abstract

Predation is one of the main selective forces in nature, frequently selecting for crypsis in prey. Visual crypsis usually implies the deposition of pigments in the integument. However, acquisition, synthesis, mobilisation and maintenance of pigments may be physiologically costly. Here, I develop an optimisation model to analyse how pigmentation costs may affect the evolution of crypsis. The model provides a number of predictions that are easy to test empirically. It predicts that imperfect crypsis should be common in the wild, but in such a way that pigmentation is less than what is required to maximise crypsis. Moreover, optimal crypsis should be closer to “maximal” crypsis as predation risk increases and/or pigmentation costs decrease. The model predicts for intraspecific variation in optimal crypsis, depending on the difference in the predation risk or the costs of pigmentation experienced by different individuals.