Background Melanic patterns such as horizontal stripes, vertical bars and spots are common among teleost fishes and often serve roles in camouflage or mimicry. Extensive research in the zebrafish model has shown that the development of horizontal stripes depends on complex cellular interactions between melanophores, xanthophores and iridophores. Little is known about the development of horizontal stripes in other teleosts, and even less is known about bar or spot development. Here, we compare chromatophore composition and development of stripes, bars and spots in two cichlid species of sand-dwellers from Lake Malawi-Copadichromis azureus and Dimidiochromis compressiceps. Results (1) In D. compressiceps, stripes are made of dense melanophores underlaid by xanthophores and overlaid by iridophores. Melanophores and xanthophores are either loose or absent in interstripes, and iridophores are dense. In C. azureus, spots and bars are composed of a chromatophore arrangement similar to that of stripes but are separated by interbars where density of melanophores and xanthophores is only slightly lower than in stripes and iridophore density appears slightly greater. (2) Stripe, bar and spot chromatophores appear in the skin at metamorphosis. Stripe melanophores directly differentiate along horizontal myosepta into the adult pattern. In contrast, bar number and position are dynamic throughout development. As body length increases, new bars appear between old ones or by splitting of old ones through new melanophore appearance, not migration. Xanthophore and iridophore distributions follow melanophore patterns. (3) Metamorphic pigmentation arises in cichlids in a fashion similar to that described in zebrafish: melanophore progenitors derived from the medial route of neural crest migration migrate from the vicinity of the neural tube to the skin during metamorphosis. Conclusion The three pigment cell types forming stripes, bars and spots arise in the skin at metamorphosis. Stripes develop by differentiation of melanophores along horizontal myosepta, while bars do not develop along patent anatomical boundaries and increase in number in relation with body size. We propose that metamorphic melanophore differentiation and migratory arrest upon arrival to the skin lead to stripe formation, while bar formation must be supported by extensive migration of undifferentiated melanophores in the skin.

中文翻译：

---

马拉维湖沙栖慈鲷的条状、条纹和斑点发育。

背景 水平条纹、竖条和斑点等黑色素图案在硬骨鱼中很常见，通常在伪装或模仿中发挥作用。对斑马鱼模型的广泛研究表明，水平条纹的发育取决于黑色素细胞、黄色细胞和虹膜细胞之间复杂的细胞相互作用。对其他硬骨鱼水平条纹的发育知之甚少，对条形或斑点发育的了解更少。在这里，我们比较了来自马拉维湖 - Copadichromis azureus 和 Dimidiochromis compressiceps 的两种沙栖丽鱼科鱼的色素细胞组成和条纹、条形和斑点的发育。结果 (1) 在 D. compressiceps 中，条纹由黄色细胞下方和虹彩细胞覆盖的致密黑色素细胞构成。黑色素细胞和黄色素细胞在条纹间松散或缺失，而虹彩细胞密集。在 C. azureus 中，斑点和条纹由类似于条纹的色素细胞排列组成，但由条纹间隔开，其中黑色素细胞和黄色素细胞的密度仅略低于条纹，而虹彩细胞密度似乎略高。(2)变态时皮肤出现条纹、条形和斑点色素体。条纹黑色素细胞沿水平肌隔直接分化成成人模式。相比之下，条数和位置在整个开发过程中都是动态的。随着体长的增加，新的条纹出现在旧的条纹之间，或者通过新的黑色素细胞出现而不是迁移来分裂旧的条纹。黄色素细胞和虹彩细胞分布遵循黑色素细胞模式。(3) 慈鲷中的变质色素沉着以类似于斑马鱼中描述的方式出现：源自神经嵴迁移内侧路线的黑色素细胞祖细胞在变态过程中从神经管附近迁移到皮肤。结论 形成条纹、条状和斑点的三种色素细胞类型在变态皮肤中出现。条纹通过黑色素细胞沿水平肌隔膜的分化而形成，而条形不沿明显的解剖学边界形成，并且数量随着体型的增加而增加。我们提出变质黑色素细胞分化和到达皮肤后的迁移停滞导致条纹形成，而条形形成必须由皮肤中未分化黑色素细胞的广泛迁移支持。源自神经嵴迁移内侧路线的黑素细胞祖细胞在变态过程中从神经管附近迁移到皮肤。结论 形成条纹、条状和斑点的三种色素细胞类型在变态皮肤中出现。条纹通过黑色素细胞沿水平肌隔膜的分化而形成，而条形不沿明显的解剖学边界形成，并且数量随着体型的增加而增加。我们提出变质黑色素细胞分化和到达皮肤后的迁移停滞导致条纹形成，而条形形成必须由皮肤中未分化黑色素细胞的广泛迁移支持。源自神经嵴迁移内侧路线的黑素细胞祖细胞在变态过程中从神经管附近迁移到皮肤。结论 形成条纹、条状和斑点的三种色素细胞类型在变态皮肤中出现。条纹通过黑色素细胞沿水平肌隔膜的分化而形成，而条形不沿明显的解剖学边界形成，并且数量随着体型的增加而增加。我们提出变质黑色素细胞分化和到达皮肤后的迁移停滞导致条纹形成，而条形形成必须由皮肤中未分化黑色素细胞的广泛迁移支持。结论 形成条纹、条状和斑点的三种色素细胞类型在变态皮肤中出现。条纹通过黑色素细胞沿水平肌隔膜的分化而形成，而条形不沿明显的解剖学边界形成，并且数量随着体型的增加而增加。我们提出变质黑色素细胞分化和到达皮肤后的迁移停滞导致条纹形成，而条形形成必须由皮肤中未分化黑色素细胞的广泛迁移支持。结论 形成条纹、条状和斑点的三种色素细胞类型在变态皮肤中出现。条纹通过黑色素细胞沿水平肌隔膜的分化而形成，而条形不沿明显的解剖学边界形成，并且数量随着体型的增加而增加。我们提出变质黑色素细胞分化和到达皮肤后的迁移停滞导致条纹形成，而条形形成必须由皮肤中未分化黑色素细胞的广泛迁移支持。