Correlations between pigment categories
To test whether pteridines replace carotenoids with a similar hue (carotenoid-mimicry hypothesis; Grether et al. 1999), we examined the relationships between either red ketocarotenoids and drosopterin, or yellow-orange dietary carotenoids and xanthopterin. Neither relationship was significant (Figure 3), although there were significant associations between other pigment categories. Specifically, there was a significant positive correlation between the concentration of dietary carotenoids and ketocarotenoids, and between other pteridines and xanthopterin, and a negative correlation between xanthopterin and ketocarotenoids (Figure 3).