Abstract
Carotenoid-based colours are a textbook example of honest signalling
because carotenoids must be acquired from the environment. However, many
species produce similar colours
using self-synthesised pteridine
pigments. A compelling but untested hypothesis is that pteridines
compensate for low environmental availability of carotenoids because it
is metabolically cheaper to synthesise pteridines than to acquire and
sequester carotenoids. Based on a phylogenetic comparative analysis of
11 pigment concentrations in skin tissue of agamid lizards, we show that
pteridine concentrations are higher and carotenoid concentrations lower
in less productive environments. Both carotenoid and pteridine pigments
were present in all species, but only pteridine concentrations explained
colour variation among species. Furthermore, pigment concentrations were
uncorrelated with indices of sexual selection. These results suggest
that variation among species in pteridine synthesis compensates for
environmental availability of carotenoids and challenge the paradigm of
honest carotenoid signalling in vertebrates with complex colour
production mechanisms.