The stripes of Zebrafish: Development and evolution of biological aesthetics
Max-Planck-Institut für Entwicklungsbiologie, Tübingen, Germany
Colour patterns are prominent features of most animals; they play an important role in social communication such as kin recognition, sexual atrraction, camouflage and aposematism.Colour patterns are highly variable and evolve rapidly leading to large diversities between species even within a single genus. Despite their importance as targets for both, natural and sexual selection, little is known about the development and evolution of colour patterns in vertebrates.The zebrafish (Danio rerio) displays a conspicuous pattern of alternating blue and golden stripes on the body and on the anal- and tailfins composed of pigment cells– melanophores, iridophores and xanthophores– distributed in three superimposed monolayers under the skin. The pigment cells originate from neural crest-derived multipotent stem cells associated with the dorsal root ganglia of the peripheral nervous system and share a lineage with neurons and glia of the peripheral nervous system. The proliferation of pigment cells is regulated by competitive interactions among cells of the same type. This mode of colouring the skin is probably common to fish, whereas different patterns emerge by species specific cell interactions among the different pigment cell types. These interactions are mediated by membrane-bound channels involved in direct cell contact between the pigment cells, as well as unknown cues provided by the tissue environment.
The colour patterns in closely related Danio species are amazingly different; their variation offers a great opportunity to investigate the genetic and developmental basis of colour pattern evolution in vertebrates. Exciting technical developments of the recent years, especially the novel possibilities of genome editing with the CRISPR/Cas9 system, allow to expand from model organisms into other species and directly test the function of genes by targeted knock outs and allele replacements. Thus, models and hypotheses about pigment pattern formation derived from zebrafish can now be tested in other Danio species. These studies will lay the foundation to understand not only the genetic basis of colour pattern variation between Danio species, but also the evolution of colour patterns in other vertebrates.