A greater diversity of chromatophore types underlies body coloration in reptiles, amphibians and fish, with seven types described in fish: xanthophores, erythrophores, iridophores, leucophores, melanophores, cyanophores and erythro-iridophores. Other colors seen in birds and mammals result from food-derived pigments interacting with skin extracellular matrix. Melanocytes may produce different kinds of melanin pigment to produce colors ranging from yellowish (pheomelanin) to black (eumelanin). The melanocyte is the only pigment cell type, or chromatophore, found in birds and mammals. Various mechanisms underlie the diversity of colors and color patterns observed among vertebrates. As such, coloration likely plays an important role in the creation and maintenance of biodiversity, yet the genetic and developmental changes required for the evolution of new patterns with adaptive value remain largely unknown. The evolutionary diversification of body coloration is a fascinating subject because body color is at the center of multiple selective pressures, such as light protection, female mate choice and predation. 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. 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. The three pigment cell types forming stripes, bars and spots arise in the skin at metamorphosis. (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. Xanthophore and iridophore distributions follow melanophore patterns. As body length increases, new bars appear between old ones or by splitting of old ones through new melanophore appearance, not migration. In contrast, bar number and position are dynamic throughout development. Stripe melanophores directly differentiate along horizontal myosepta into the adult pattern. (2) Stripe, bar and spot chromatophores appear in the skin at metamorphosis. 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. Melanophores and xanthophores are either loose or absent in interstripes, and iridophores are dense. compressiceps, stripes are made of dense melanophores underlaid by xanthophores and overlaid by iridophores. 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. Little is known about the development of horizontal stripes in other teleosts, and even less is known about bar or spot development. Extensive research in the zebrafish model has shown that the development of horizontal stripes depends on complex cellular interactions between melanophores, xanthophores and iridophores. Melanic patterns such as horizontal stripes, vertical bars and spots are common among teleost fishes and often serve roles in camouflage or mimicry.
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