Sexual dichromatism — a difference in coloration between males and females — is central to the study of ornamentation, mate choice, and sexual selection. Here, we show that carotenoid-based dichromatism in mosaic canaries, a hybrid product between the sexually dichromatic red siskin and monochromatic canaries, is controlled by the carotenoid-cleaving enzyme Beta-Carotene Oxygenase 2 (BCO2). Dichromatism in mosaic canaries is explained by differential carotenoid degradation in the integument of each sex, rather than sex-specific variation in physiological functions such as pigment uptake or transport. Transcriptome analyses suggest that carotenoid degradation in the integument might be a common mechanism contributing to sexual dichromatism in other finches. Our findings demonstrate how differences in ornamental coloration between sexes can evolve through simple molecular mechanisms controlled by genes of major effect.

File “snp_call_freebayes.vcf.gz” – includes all the variants identified using whole-genome sequencing of DNA pools of six canary breeds, one wild population, and red siskin. The breeds or populations are listed in the vcf file in the following order: mosaic red, mosaic yellow, red lipochrome, black red intense, gibber italicus, white recessive, wild, and red siskin.

File “genotyping.xlxs” – includes individual genotypes for 52 SNPs and 78 canaries and red siskins (mosaic individuals = 56; common canaries = 14; red siskins = 8). The SNPs were selected from the whole-genome sequencing data among those characterized by diagnostic alleles between wild canaries and red siskin. Positions homozygous for the siskin allele are represented in red, positions homozygous for the canary allele in yellow, and positions heterozygous in orange. The location of the SNPs in scaffold NW_007931177 of the canary reference genome is indicated. Missing data is indicated by the number 1 and a white box.

Files “*_transcriptome_assembly.fa” – De novo transcriptome assemblies for three species: Atlantic canary, European serin, and house finch.

File "DE_genes_sex_dichromatism.xlsx" – lists of differentially expressed genes in pairwise comparisons