| 口試日期：2026 |
| 學位類別：碩士 |
| 指導教授：唐品琦 |
| 研究生：黎進利 |
| 摘要 |
| Feather coloration in birds, including the Mallard duck (Anas platyrhynchos), exhibits remarkable diversity both among and within species, reflecting its ecological significance and the influences of natural and sexual selection. Melanin-based pigmentation contributes significantly to plumage variation, arising mainly from two forms: eumelanin, which produces dark brown to black tones, and pheomelanin, which produces reddish to yellow tones. This work examined promoter activity of pigmentation-related genes in Mallard ducks and explored factors influencing regional specificity and sexual dimorphism in plumage. The promoter regions of ASIP, TYR, TYRP1, ER, and AR were cloned and analyzed using a dual-luciferase reporter system, with each region predicted to carry Hox binding motifs. The results indicated that the promoters of ASIP, TYRP1, and ER exhibited significantly higher luciferase activity, whereas TYR and AR did not drive reporter expression. Given these predicted binding sites, the expression of five Hox genes (HoxA3, HoxB8, HoxC8, HoxC13, HoxD8) in feather follicles dissected from three body regions (head, saddle, and abdominal) in male and female Mallards was further analyzed. HoxA3 expression varied with both region and sex. HoxC8 was detected in the saddle and abdominal regions, particularly in females, but remained below the detection threshold in the head region. The expression patterns of HoxB8, HoxC13, and HoxD8 were complex and sex- and region-dependent. Additionally, castrated male Mallards were injected with estradiol (E2) to investigate hormonal effects on plumage development. E2 treatment was associated with female-like phenotypes, including a significant reduction in feather length in the head region and a non-significant tendency toward shortening in the saddle, although the treated feathers remained longer than those of females. At the molecular level, E2 altered pigmentation-related gene expression in a region-specific manner. In the head, MITF and KITLG were significantly upregulated and TYR showed a similar but non-significant increase, while TYRP1 and PMEL were downregulated. In the saddle region, ASIP was strongly increased, whereas MITF, TYRP1, and PMEL were reduced compared with the controls. Furthermore, the saddle feathers showed approximately 2-fold higher TYRP1 protein levels in the E2 treated group than those in the groups of female, control, and untreated male ducks by immunohistochemistry (IHC) analysis. ERα protein expression showed a region-specific pattern: it was significantly higher in E2 treated and male head follicles than in control and female groups, whereas in the saddle, neither ERα nor MITF differed between control and E2 treated groups, with females showing the highest ERα levels. Notably, E2 treatment significantly increased HoxB8 expression in head follicles, reaching levels comparable to females. HoxC8 expression in the same region also tended to increase after E2 treatment, but the change was not statistically significant, with the highest levels observed in females. A JASPAR-based prediction also revealed that the ERα promoter contains a potential HoxC8 binding site, raising the possibility of a local link between estrogen signaling and Hox activity that remains to be tested. These findings suggest that both Hox transcription factors and estradiol may contribute to the regional and sex-related differences in plumage pigmentation in Mallard ducks, with effects that appear to depend on body region. Keywords: Estradiol, Feather pigmentation, Homeobox gene, Sexual dimorphism. |