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).