In a previous post I discussed color patterns in butterfly wings. Each scale is a single color. In some butterflies, colors are produced by pigments. The Tiger Swallowtail below has yellow, black and blue scales on its wing. In these scales the biochemical pathway to produce each color is turned on or off depending on the location of the cells.
The yellow color is due to papiliochrome. This pigment is synthesized from amino acids. The direct precursors are kynurenine and B-alanine. Cells that make papiliochrome take up kynurenine from the hemolymph where it is abundant in swallowtails.
The black scales are produced by melanin. Melanin is produced by the oxidation of cell components by quinones. The same process that tans the insect cuticle and produces hard plates creates the melanin in the black wing scales.
The blue color is due to bilichrome, a blue pigment widespread in nature. Bilichrome contains porphyrin rings.
The pigments used in butterfly scales are relatively common or closely connected to other important biological molecules. The control of pigment production by wing cells is a key to understanding pattern formation in insect wings.
Why is pattern formation important? The process of pattern formation is likely to be similar in most living organisms. Many aspects of human biology are based on “patterns” specific to our cells in a defined location. Understanding pattern formation may lead to therapies that correct defects or even regeneration of missing parts.