CYP2J19 mediates carotenoid colour introgression across a natural avian
hybrid zone
Abstract
It has long been of interest to identify the phenotypic traits that
mediate reproductive isolation between related species, and more
recently, the genes that underpin them. Much work has focused on
identifying genes associated with animal colour, with the candidate gene
CYP2J19 identified in laboratory studies as the ketolase converting
yellow dietary carotenoids to red ketocarotenoids in birds with red
pigments. But evidence that CYP2J19 explains variation between red and
yellow feather coloration in wild populations of birds is lacking.
Hybrid zones between related species provide the opportunity to identify
genes associated with specific traits. Here we investigate genomic
regions associated with forecrown colour in red-fronted and
yellow-fronted tinkerbirds across a hybrid zone in southern Africa. We
sampled 79 individuals, measuring spectral reflectance of forecrown
feathers as well as scoring colours from photographs. We performed a
genome-wide association study to identify associations with
carotenoid-based coloration, using double-digest RAD sequencing aligned
to a short-read whole genome of a Pogoniulus tinkerbird that we
assembled. Admixture mapping using 104,933 SNPs identified a region of
chromosome 8 that includes CYP2J19 as the only locus with more than two
SNPs significantly associated with both crown hue and crown score. The
hybrid zone was bimodal with asymmetric backcrossing, consistent with
the hypothesis that yellow-fronted females mate more often with
red-fronted males than vice versa. Female red-fronted tinkerbirds mating
assortatively with red-crowned males may reinforce species divergence
and is consistent with the hypothesis that converted carotenoids are an
honest signal of quality.