Most animals are coloured; colours not only protect them from harmful UV irradiation, but they also play important roles in inter- and intra-species communication. Colour patterns, often strikingly elaborate, serve as camouflage in predator-avoidance, they have roles in kin recognition and in mate selection. Colour patterns are highly variable and evolve rapidly, and as direct targets of natural and sexual selection they are of high evolutionary relevance. An understanding of the mechanisms that underlie pigmentation and colour pattern formation is an important step towards comprehending the evolution of bio-diversity.
The pigment-producing cells in vertebrates originate from the neural crest, a transient primordium of multi-potent cells located at the dorsal neuro-ectodermal ridge, from which progenitor cells migrate out into the periphery to develop a variety of structures and tissues. Neural crest evolved at the protochordate-vertebrate transition; it is a developmental innovation that allowed vertebrates to become both, large and colourful. Of highest evolutionary significance is the formation of a true head with neural crest-derived skull bones and jaw.
Using genetic techniques for long-term cell-labelling we discovered recently that the pillar cells of the gills, the respiratory organs of fish that predate the appearance of the skull, are also neural crest-derived; whereas the scales, dermal bone structures protecting the body, are not (Mongera et al, 2013, Mongera and Nüsslein-Volhard, 2014
). Other neural crest-derived structures include the neurons of the peripheral nervous system, the glia, and the pigment cells.