Abstract
BackgroundColoration and color patterning belong to the most diverse phenotypic traits in animals. Particularly, teleost fishes possess more pigment cell types than any other group of vertebrates. As the result of an ancient fish-specific genome duplication (FSGD), teleost genomes might contain more copies of genes involved in pigment cell development than tetrapods. No systematic genomic inventory allowing to test this hypothesis has been drawn up so far for pigmentation genes in fish, and almost nothing is known about the evolution of these genes in different fish lineages.ResultsUsing a comparative genomic approach including phylogenetic reconstructions and synteny analyses, we have studied two major pigment synthesis pathways in teleost fish, the melanin and the pteridine pathways, with respect to different types of gene duplication. Genes encoding three of the four enzymes involved in the synthesis of melanin from tyrosine have been retained as duplicates after the FSGD. In the pteridine pathway, two cases of duplicated genes originating from the FSGD as well as several lineage-specific gene duplications were observed. In both pathways, genes encoding the rate-limiting enzymes, tyrosinase and GTP-cyclohydrolase I (GchI), have additional paralogs in teleosts compared to tetrapods, which have been generated by different modes of duplication. We have also observed a previously unrecognized diversity of gchI genes in vertebrates. In addition, we have found evidence for divergent resolution of duplicated pigmentation genes, i.e., differential gene loss in divergent teleost lineages, particularly in the tyrosinase gene family.ConclusionMainly due to the FSGD, teleost fishes apparently have a greater repertoire of pigment synthesis genes than any other vertebrate group. Our results support an important role of the FSGD and other types of duplication in the evolution of pigmentation in fish.
Highlights
Coloration and color patterning belong to the most diverse phenotypic traits in animals
Coloration is the result of diverse pigments synthesized by pigment cells or chromatophores, which are derived from the neural crest
We find that the fish-specific genome duplication (FSGD) had a deep impact on the melanin synthesis pathway, with three out of four enzyme-encoding genes being duplicates in teleosts
Summary
Coloration and color patterning belong to the most diverse phenotypic traits in animals. Teleost fishes possess more pigment cell types than any other group of vertebrates. As the result of an ancient fish-specific genome duplication (FSGD), teleost genomes might contain more copies of genes involved in pigment cell development than tetrapods. Coloration and color patterning of skin, scales, feathers, and hair belong to the most diverse phenotypic traits in vertebrates and have a plethora of functions such as camouflage, warning or threatening of predators, and species recognition [1,2]. BMC Evolutionary Biology 2007, 7:74 http://www.biomedcentral.com/1471-2148/7/74 able differences in the number of chromatophore types among vertebrate groups. Some pigment cell types in teleosts are even further partitioned into distinct sublineages that are under different genetic control [3,4]
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