Figure 1.

The long‐term development of background matching of Carcinus maenas for approximately 10 weeks of rearing under controlled conditions. A 2×2 factorial design was used utilizing two initial crab colour types and two rearing backgrounds in a common garden experiment (a). Two artificial background types, mudflat and rock pool, were both constructed using aquarium gravel. The crabs representing two initial shade types, dark and pale, were reared on these background types, and changes in their carapace coloration were recorded. Lines around the crabs represent treatment group legends in the panels (b–e). Solid green: dark‐shaded crabs on mud background; Solid blue: dark‐shaded crabs on rock pool background; Dashed green: pale‐shaded crabs on mud background; and Dashed blue: pale‐shaded crabs on rock pool background. The change in colour (b) and pattern (c) principal components obtained from normalized camera responses. The effect of colour change to chromatic (d) and luminance (e) background match (modelled through predatory fish vision, JNDs, just noticeable differences)