Morphogenesis of the dorsal pigmentary pattern in wild-type and mutant Rana pipiens

The transition from larval to adult pigmentary patterns during metamorphosis of wild-type. burnsi, and kandiyohi R. pipiens is described. Larval fusiform epidermal melanocytes form a pattern that exactly corresponds to the adult spotting pattern. It is concluded that the larval epidermal pattern expresses a “prepattern” in the larval tissue for the adult pattern. This “prepattern” is visible in kandiyohi, but not in burnsi, tadpoles. The role of the extracellular environment in pigmentary pattern determination is discussed. Gradual changes in all chromatophore densities accompany larval development, while abrupt changes accompany metamorphic climax. There is a net increase in all chromatophore densities by the completion of metamorphosis. Kandiyohi density changes differ quantitatively but not qualitatively from those of wild type. In both wild type and kandiyohi, differentiation of many new dermal melanophores in presumptive spot regions effects expression of the adult spotting pattern. The relative roles of chromatophore differentiation and mitosis in pattern expression, and the hormonal control thereof, are discussed.