Graded BMP signals modulate yellow and red color in fishes, impacting adult pigment patterns and conspecific shoaling behavior

Among the most interesting adult traits are those with roles in animal communication. Yet, developmental mechanisms by which genes drive cell behaviors in building the final forms of such traits are rarely known. In this context, pigmentation is useful because colors and patterns often provide signals in mate choice, predation avoidance, and other behaviors,¹^,²^,³ and pigmentation is unusually accessible to observation and manipulation.⁴^,⁵ Here, we focus on some of the most prominent signaling colors-red, orange, and yellow-and show how BMP signaling at the cellular level allows for a very different kind of signal at the organismal level. Using pearl danio, Danio albolineatus,⁶ we find that spatially and temporally graded BMP signals promote the development of yellow/orange xanthophores over red erythrophores in the fin of this species and a distantly related minnow, Tanichthys albonubes, and that conserved mechanisms, involving BMP co-receptor Rgmb, regulate the differentiation of other pigment cell types in corresponding locations of zebrafish, D. rerio. We further use mutants of D. albolineatus with more red or more yellow cells than the wild type to demonstrate female responsiveness to carotenoid-based color differences between males in shoaling preference assays. Our findings illustrate a chain of functions spanning hierarchical levels and provide a deeper understanding of pigmentary form and function and its evolution.