Riboflavin: a potentially important skin pigment in reptiles

Abstract Pigments not only contribute to the extraordinary diversity of animal coloration but also play vital physiological roles. Riboflavin, or vitamin B2, is a macronutrient essential for cellular metabolism and growth, and is a well-known yellow pigment produced industrially for a wide range of applications, both as a colourant and dietary supplement. Remarkably, however, its role in animal skin coloration has been largely overlooked. Using quantitative mass spectrometry, we show that high riboflavin concentrations correspond to yellow hues in the skin of two species of lizard and one snake species. The comparison of riboflavin concentrations in different skin colours within individuals provides compelling evidence that riboflavin can contribute to skin pigmentation in reptiles beyond its general role in cellular metabolism. The role of riboflavin was further corroborated by high concentrations of riboflavin in yellow blotches of the Snow morph of the corn snake. In this mutant, xanthophore pigment cells, which in wild-type corn snakes contain pteridine pigments, are heavily impacted, and the overall amount of yellow pteridines is low. Like carotenoids, riboflavin must be acquired through diet and has powerful antioxidant properties. Thus, its use in coloration may have unrecognized ecological and evolutionary implications.