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Colour change is widespread in ectotherm animals including crustaceans, insects, cephalopods, amphibians, reptiles and fish (Bagnara & Hadley 1973). There are two types of colour change, morphological and physiological, which differ in their mechanism and speed. Morphological colour change occurs due to changes in the density and quality of pigment-containing cells (chromatophores) in the dermis (a layer of the skin) and usually takes place over a timescale of days or months. For instance, a common form of morphological colour change is long-term background or chromatic adaptation, in which the animal’s colour changes to more closely resemble that of the background. Long-term background adaptation involves an increase in both the density of melanophores (melanin-containing chromatophores) and melanin pigment within the melanophores (Bagnara & Hadley 1973; Sugimoto 2002). By contrast, physiological colour change occurs due to movement (dispersion or concentration) of pigment within chromatophores and is much more rapid, taking milliseconds to hours (Bagnara & Hadley 1973; Thurman 1988). For example, short-term background adaptation generally involves movement of melanosomes (organelles containing melanin pigment) within melanophores, either becoming concentrated in the middle, resulting in lightening, or becoming dispersed throughout, resulting in darkening. The exception is cephalopods (squid, cuttlefish, octopuses and their relatives), in which colour change occurs due to contraction of the muscle fibres of specialised ‘chromatophore organs’, which comprise the chromatophore itself surrounded by …