Pigment concentrations and skin colour
Variation in skin colours was associated with the concentration of pteridines but not carotenoids (Figure 4). Specifically, redder skin hues (lower hue values) were associated with higher drosopterin concentrations, and more saturated colours were associated with higher xanthopterin, other pteridines and total pteridine concentrations (Table 2). Tissues with higher concentrations of other pteridines also had lower luminance (darker). Yellow-red tissues (including browns, N=150) had higher concentrations of drosopterin (Figure 4C), other pteridines, and ketocarotenoids compared to black/grey/white tissues (N=36; 186 tissue samples in total); whereas dietary carotenoid and xanthopterin concentrations were similar in all skin colours (Table S4, Figure S2). Additionally, skin luminance was associated with habitat productivity (PC1 95% CIs 0.716 – 8.943), with darker colours in more vegetated environments (Figure S3), but environmental PCs did not predict hue or saturation (Table S5).