All patterns great and small: Researchers uncover the origins of creatures' stripes and spots

Abstract

All patterns Jkgreat ^K&T and n Ms small ^^d^^r IM Researchers uncover the origins ^^^^^HfeH^'Mfc of creatures' stripes and spots ^^V^ By Tina Hesman Saey Howthe leopard got its spots and the zebra its stripes might not be just-so stories much lon ger. Biologists are beginning to pinpoint the molecular mechanisms animals use to deck themselves out with colorful swirls, stripes, spots and dots. Insects, fish and mammals may have different tricks. Butterflies and fruit flies, for instance, paint their wing dec orations on top of underlying patterns, such as wing veins. Fish may similarly arrange their colored scales according to a prepattern but probably decorate their fins according to mathematical principles laid out on a blank slate. And mammals' beauty marks may arise like those of fish?or via an entirely differ ent mechanism. British mathematician Alan was one of the first scientists to explain how color patterns might form. In a 1952 paper, he envisioned patterns as self assembling products of molecular reac tions created as two chemicals spread across a uniform surface. Turing's math ematical models could replicate any pattern found in nature, and scientists soon began hunting for the chemicals responsible for painting butterfly wings a d tiger stripes. But Turing has led biologists astray, charges Fred Nijhout, a developmen tal physiologist at Duke University in Durham, N.C. Mathematically it's com pletely correct, and there are some physi cal systems in which it can occur, he says. Tu ing formulated his theory before the modern era of molecular genetics, though, and biological systems don't always work the way his models predict. For one thing, skin, scales and fur aren't the blank canvases upon which envisioned color patterns paint ing themselves. Sometimes biology is a bit uncooperative because it uses more components than models tell us are nec essary,** says Sean B. Carroll, a develop mental and evolutionary biologist at the University of Wisconsin-Madison. ^ A team led by Carroll recently i found molecular evidence that