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Fig. 2. PCs derived after Varimax rotation (SPSS version 11.5) (Kelman et al., 2007) from scores of the expression of 32 chromatic and textural components (see Fig. 1) (Hanlon and Messenger, 1988) of 20 juvenile cuttlefish (mantle length 50–70 mm) placed in a 300 mm diameter arena (area 0.07 m²) on different backgrounds. Kelman and co-workers (Kelman et al., 2007) give further details of methods used for photographing the animals, scoring and PCA. Bold fonts indicate behavioural components that Hanlon and Messenger (Hanlon and Messenger, 1988) classified as body patterns. (A) PCs for pebble backgrounds of real pebbles under 5 mm Perspex, photographs of these pebbles at three contrast levels (see Fig. 3A,B) or photographs with 10 real pebbles (see Fig. 3C). For the 140 images that were graded (one per animal on each of seven backgrounds), three components (PC1–3) accounted for 47% of the total variance in the expression of the 32 behavioural components scored. A scree plot indicated that fitting further PCs was not meaningful. (B) PCs for checkerboard backgrounds (see Fig. 4). For the 60 body patterns that were graded, four PCs account for 59% of the total variance in the expression of 32 behavioural components. Fitting greater than four PCs was not meaningful. Positive values of three of the PCs correspond to body patterns identified by Hanlon and Messenger (Hanlon and Messenger, 1988): PC1 to the disruptive pattern; PC2 to the uniform stipple; and PC3 to the mottle pattern. PC4 involves two white components: white major lateral papillae (12) and white head bar (13).

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