Morphological and Physiological Colour Changes in the Animal Kingdom

Abstract Colour change is the ability of an organism to modify its colouration in response to specific stimuli. Several biological functions have been proposed to explain colour changes, including ultraviolet (UV) protection, thermoregulation, crypsis, inter‐ and intraspecific communication. Changes in body colouration are mainly performed through two types of mechanisms referred to as morphological and physiological. Mechanistically, these two types of colour changes differ in their speed and the way coloured structures are altered. The proximal causes of these colour changes are identified in a handful number of species and demonstrate that common physiological, cellular and molecular actors are at play. However, the reasons why both colour‐change types are widespread in the animal kingdom and how they have evolved are still unknown. This is partly due to a lack of knowledge about the fitness implications of colour changes, particularly their energetic costs. Key Concepts Morphological and physiological colour changes are widespread in the animal kingdom. It has been suggested that both types of colour changes have the same biological functions, which are UV protection, thermoregulation, crypsis, inter‐ and intraspecific communication. Despite differences in speed and mechanisms, similar cellular and molecular actors are at play for both types of colour changes. Colour changes are triggered by environmental stimuli, mainly light, and are regulated by the neuronal and hormonal systems. The evolution of colour‐changing abilities is still poorly understood because the consequences of colour changes on individual fitness remain to be investigated.