Pigment patterns: fish in stripes and spots

From tiger stripes to the spots on a butterfly wing, we all grow up learning about the beauty and diversity of animal pigment patterns. Such patterns are one of the most obvious traits of animals and serve a variety of functions. Some provide camouflage (zebra stripes) or warnings (the colors of poison arrow frogs). Other patterns have roles in social aggregation and mate choice (guppies), and have important roles in adaptive radiations and speciation (African cichlid fishes). Given their prominence and ecological functions, pigment patterns often are targets of natural selection and thus of particular interest to evolutionary biologists. They have been of long-standing interest to developmental and cell biologists as well: their accessibility to observation and manipulation has made them a classic and enduring system for studying basic genetic and cellular mechanisms. Recent years have seen the emergence of pigment patterns specifically as a model for postembryonic development. Discovering why adult organisms look the way they do is critical to understanding the evolution of morphology. Despite great strides in understanding embryogenesis, however, we still know little about the generation of adult form. In this regard, pigment patterns are an especially tractable system for identifying mechanisms of pattern formation and morphogenesis that make an adult. They also offer the prospect of truly integrative research spanning several levels of biological organization, from molecules to cells and phenotypes, and from individuals to populations and species. One prime model organism for dissecting mechanisms of pigment pattern formation and evolution is the zebrafish, Danio rerio.