Showing their stripes The adaptive radiation of East African cichlids has led to more than 1200 species across a number of lakes. Across these species, many convergent traits have emerged, including the presence or absence of horizontal stripes. Kratochwil et al. show that the appearance or loss of stripes is related to changes in the agouti-related peptide 2 gene, which acts as a kind of on-off switch for stripe generation (see the Perspective by Gante). This action has enabled rapid and repeated evolution of stripes across this speciose radiation. Science, this issue p. 457; see also p. 396 The color patterns of African cichlid fishes provide notable examples of phenotypic convergence. Across the more than 1200 East African rift lake species, melanic horizontal stripes have evolved numerous times. We discovered that regulatory changes of the gene agouti-related peptide 2 (agrp2) act as molecular switches controlling this evolutionarily labile phenotype. Reduced agrp2 expression is convergently associated with the presence of stripe patterns across species flocks. However, cis-regulatory mutations are not predictive of stripes across radiations, suggesting independent regulatory mechanisms. Genetic mapping confirms the link between the agrp2 locus and stripe patterns. The crucial role of agrp2 is further supported by a CRISPR-Cas9 knockout that reconstitutes stripes in a nonstriped cichlid. Thus, we unveil how a single gene affects the convergent evolution of a complex color pattern. A genetic switch that can turn horizontal stripe production on or off in East African cichlids is dissected. A genetic switch that can turn horizontal stripe production on or off in East African cichlids is dissected.

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