Environmental gradients and pigment concentrations
Total carotenoid concentration was significantly associated with
environmental gradients. Individuals living in arid environments with
low vegetations productivity (and thus potential carotenoid limitation;
environmental PC1) had a lower concentration of total carotenoids
(Figure 2a, Table 1, r2= 0.16). This association was
driven by dietary yellow carotenoids (Table S2) because they comprise
the great bulk of total carotenoids; there was no association between
red ketocarotenoids and environmental PC1 (Table S2). Individuals in
less productive environments also had a higher concentration of total
pteridines (Figure 2b, Table 1, r2= 0.14), and
therefore there was a significantly lower ratio of carotenoids to
pteridines in more productive environments (Figure 2c, Table 1,
r2= 0.17).
To further explore the link between environmental PC1 and pigment
concentrations, we examined the association between specific
environmental variables and total carotenoids, total pteridines, or
their ratio (Table S3). The strongest drivers of pigment concentration
were aridity and radiation of the warmest quarter. Species with low
carotenoids, high pteridines and low ratio of carotenoids to pteridines
were found in arid environments with high summer solar radiation.
There was no significant association between sexual selection indices
and pigment concentration in the whole dataset analysis (Table 1) or at
the species-level (Table S1), although there was a trend for higher
total carotenoid concentration in species with higher sexual size
dimorphism (Figure 2D).