Camouflage through colour change: mechanisms, adaptive value and ecological significance

Abstract

Animals from a wide range of taxonomic groups are capable of colour change, of which camouflage is one of the main functions. A considerable amount of past work on this subject has investigated species capable of extremely rapid colour change (in seconds). However, relatively slow colour change (over hours, days, weeks and months), as well as changes arising via developmental plasticity are probably more common than rapid changes, yet less studied. We discuss three key areas of colour change and camouflage. First, we review the mechanisms underpinning colour change and developmental plasticity for camouflage, including cellular processes, visual feedback, hormonal control and dietary factors. Second, we discuss the adaptive value of colour change for camouflage, including the use of different camouflage types. Third, we discuss the evolutionary-ecological implications of colour change for concealment, including what it can tell us about intraspecific colour diversity, morph-specific strategies, and matching to different environments and microhabitats. Throughout, we discuss key unresolved questions and present directions for future work, and highlight how colour change facilitates camouflage among habitats and arises when animals are faced with environmental changes occurring over a range of spatial and temporal scales.This article is part of the themed issue 'Animal coloration: production, perception, function and application'.

Keywords: behaviour; camouflage; chromatophores; colour change; predator–prey interactions.

Figure 1.

Animals can modify their appearance over varied timescales. Some fish, like rock gobies (Gobius paganellus), change brightness and colour in less than a minute. Shore crabs (Carcinus maenas) change brightness over 2 h, becoming darker on black (left images) and lighter on white backgrounds (right images). Chameleon prawns (Hippolyte varians) undergo day–night changes from their diurnal type (here a brown morph) to blue–grey at night. Colour change also often occurs over longer periods. Red chameleon prawns change to green when on green seaweed for 20 days (top), and begin to change from green to yellow–red when on red seaweed (bottom; though this direction of change seems slower). Shore crabs substantially change appearance as they moult over weeks and months. Here, the top individual changes from dark to light post-moult after being kept on a white substrate. The bottom images show an individual changing colour and pattern with moult after having been kept on a light yellow substrate. Changes also occur with ontogeny, with juvenile crabs (left column) highly diverse in appearance, but variation declining from subadults (middle column) to adults (right column).

Figure 2.

Intraspecific diversity and matching to different backgrounds. The chameleon prawn (Hippolyte varians) has considerable intraspecific variation, with multiple relatively homogeneous and interchangeable colour types ranging from red to green (top row), in addition to seemingly fixed transparent morphs (bottom row). These different morphs allow camouflage against different seaweed types.