Abstract

Sexual dimorphism of plumage color is common in avians. A well-known example is mallard, in which drakes exhibit green head feathers, while females exhibit dull head feather color. Through microscopy observations, melanin was observed to be continuously deposited in feather barbules and to form a two-dimensional hexagonal lattice, which conferred the green feather coloration of drakes. Additionally, transcriptome analysis revealed that most pigmentation genes were highly expressed in feather follicles during the development of green feathers, which may contribute to melanin deposition. We identified 18 consensus differentially expressed genes in feather follicles by comparing the transcriptome differences in the male head vs. female head, male head vs. male back, and male head in the 7th week vs. male head in the 11th week. Among these genes, TYRP1 located on Z-chromosome of the mallard genome, showed an increasing trend in the feather follicles of drake heads during green feather development. In particular, its expression was 256 and 32 times higher in the head follicles of males than in those of the female head and the male back, respectively. Hence, the green feathers were determined by TYRP1 through sex-biased expression, which is common for genes linked with Z-chromosome in avians. The differential expression of TYRP1 in different body parts of males and among different time points may be due to differences in cis-regulation by transcription factors. We also demonstrated that the beautiful feather color of other male avians is largely caused by the sex-biased expression of pigmentation genes linked with Z-chromosome.