Abstract
Carotenoids are important pigments producing integument coloration;
however, their dietary availability may be limited in some environments.
Many species produce red to yellow hues
using a combination of carotenoids
and self-synthesised pteridine pigments. A compelling but untested
hypothesis is that pteridines replace carotenoids in environments where
carotenoid availability is limited. Based on a phylogenetic comparative
analysis of pigment concentrations in agamid lizards, we show that
environmental gradients predict
the ratio of carotenoids to pteridines; carotenoid concentrations are
lower and pteridine concentrations higher in arid environments with low
vegetation productivity. Both carotenoid and pteridine pigments were
present in all species, but only pteridine concentrations explained
colour variation among species and
there were no correlations between
carotenoid and pteridine pigments with similar hue. These results
suggest that pteridine pigments replace carotenoids in
carotenoid-limited environments, irrespective of skin hue, presumably
because it is metabolically cheaper to synthesise pteridines than to
acquire and sequester carotenoids when carotenoids are rare.