| Description: |
(A) Scheme of the two stages of feather transitions from natal downs to adult feathers. The primary feather transition pertains solely to immature plumage exhibiting a gradient of gray [ 5 ]. Regional domains are established during embryonic development and maintained through juvenile stages. The secondary feather transition leads to the emergence of sex dichromatic plumage through a shift in the pigmentation pathway during the replacement of juvenile male or female feathers with mature feathers. (B) The predicted and hypothetical concentrations of pheomelanin and eumelanin in seven colors of zebra finch plumage. The red cheek feathers and brown flanking feathers of males are predicted to be primarily composed of pheomelanin pigments (over 90%) [ 31 ], although eumelanin pigments are also present. This suggests that the production of pheomelanin and eumelanin is not entirely exclusive within a single feather. In other words, a higher proportion of pheomelanin results in redder feathers, while a higher proportion of eumelanin results in darker, blacker feathers. (C) Two types of plumage variants arise from mutations. Chestnut Flank White (CFW), characterized by lighter red cheek coloring, is predicted by breeders to result from mutations on the sex chromosomes. Black Cheek (BC), characterized by black cheek coloring, is predicted to result from autosomal mutations. (D–F) Secondary feather transition, marking the transition from juvenile to adult feather forms. (D) 11-day-post-hatching (D11) juveniles with clear feather tracts and naked skin. (E) Craniofacial skin of 14-day-post-hatching (D14) juveniles is completely covered by feathers. (F) Craniofacial plumage of mature wild-type adult finches. Male with bright red cheek patch is shown in the left panel, while female with cryptic gray cheek patch is shown in the right panel. (D’–F’) Feather tract domain boundaries seen in (D–F) are delineated, and the specific name of each domain is listed. The crown domain is referred to as scalp and the ear patch domain termed ... |