弗氏海豚體側條紋色素沉澱的組織學研究

Abstract

弗氏海豚(Lagenodelphis hosei)是一種台灣常見擱淺的鯨豚，同時也是一種體側膚色會隨著年齡變化的鯨豚類，然而鮮少對此有相關報導。過去對弗氏海豚傷口癒合機制的研究揭示了不同部位表皮黑色素細胞數量以及色素沉澱的不均勻分布，但似乎在特定區域採集的樣本中黑色素細胞數量異常增加，並且這些樣本都分布於體側黑帶的範圍，這可能代表黑帶區域有著獨特的色素沉澱機制。 為了調查黑帶獨特的色素沉澱機制，本研究採集來自台灣周遭擱淺的弗氏海豚全身性不同膚色的皮膚組織，利用免疫組織化學染色計算基底層黑色素細胞的數量從，以及黑色素染色法量化色素沉澱從而得到膚色與皮下黑色素細胞數量的關係。結果表明，黑帶區域與背側和腹側的皮膚相比有多的色素細胞，但表皮色素沉澱卻比正常皮膚更少，這可能暗示黑帶區域在未來有著更高的色素沉澱潛力。此外，參與陸生動物體色分布的基因ASIP似乎也在黑帶區域的色素沉澱機制中扮演了關鍵的角色，不僅在黑帶與正常皮膚的交界區表現，同時與黑帶區域內的膚色深淺變化呈現負相關。本研究描述了弗氏海豚全身性的色素沉澱以及黑色素細胞分布，證實黑帶區域的獨特性，並首次發現ASIP參與在體色會伴隨年齡改變的物種中可能影響色素沉澱的分佈，為哺乳動物變色機制提供了新的方向。進一步研究可能對生物變色背後的生態策略有更深的了解。

Fraser’s dolphin (Lagenodelphis hosei) is one of the commonly stranded cetacean species in Taiwan and is also known for exhibiting age-related changes in lateral skin pigmentation. However, there are few studies documenting this phenomenon. Previous research on wound healing mechanisms in Fraser’s dolphins has revealed regional variation in both the number of epidermal melanocytes and the distribution of pigmentation. Notably, certain samples collected from specific body regions demonstrated an abnormally high number of melanocytes. These samples were consistently located within the lateral black stripe area, suggesting the presence of a unique pigmentation mechanism in this region. To investigate the distinctive pigmentation process in the black stripe area, this study collected skin samples with varying coloration from Fraser’s dolphins stranded along the coast of Taiwan. The number of basal melanocytes was quantified using immunohistochemistry staining, and pigment deposition was assessed through Fontana-Masson staining. These methods enabled the analysis of the relationship between skin color and subepidermal melanocyte density. Results demonstrated that the black stripe region harbors a significantly higher number of melanocytes compared to the dorsal and ventral skin, yet paradoxically exhibits less epidermal pigment deposition than areas of normal skin. This may indicate a latent potential for increased pigmentation in the black stripe region. Furthermore, the agouti signaling protein (ASIP) gene—known to regulate pigmentation patterns in terrestrial animals—appears to play a critical role in the pigmentation mechanism of the black stripe. ASIP expression was detected at the boundary between the black stripe and adjacent normal skin and was also correlated with intraregional variation in pigmentation intensity within the stripe. This study provides the first comprehensive characterization of melanocyte distribution and pigment deposition across the body of L. hosei, confirms the unique nature of the black stripe region, and, for the first time, implicates ASIP in the regulation of pigmentation in a cetacean species with age-dependent color change. These findings offer new insights into the mechanisms of mammalian color variation and suggest future research directions for understanding the ecological strategies underlying pigmentation dynamics.