DNA methylation of the endothelin receptor B makes blue fish yellow

Natural selection shapes traits during evolution including animal coloration known to be important for concealment and communication and color has been particularly salient in the explosive radiation of cichlid fish species in the rift valley lakes of East Africa. Though selection can produce variation in color via genetic substrates during early development, plasticity in coloration can occur through endocrine, neural and transcriptional cues in response to various environmental stimuli. It is well known that some animals often change color to match their visual ecology. Adult male cichlid fish (Astatotilapia burtoni, Lake Tanganyika) can switch between blue and yellow body colors. Different colors result from the expression of pigment-bearing cells, which differ in density and function between these two color morphs. We show that A. burtoni switches from yellow to blue depending on their visual environment by downregulating endothelin receptor B (EdnRB) mRNA via DNA hypermethylation at a single cytosine residue within its promoter. EdnRB functions in yellow chromatophores to signal the aggregation of yellow pigments, making yellow less visible. Taken together, the regulation of EdnRB through DNA methylation in yellow chromatophores, in part, contributes to pigmentation changes from blue to yellow, depending on visual environment.