Fading to black doesn’t empower fish

Field studies of three-spined stickleback fish dash a textbook example of an evolutionary principle, claims an evolutionary biology team. Males of Gasterosteus aculeatus typically turn red on their bellies and blue-green on top when breeding—unless they live in Washington’s Chehalis River watershed. There, males turn jet-black.

That quirk achieved textbook status as the only documented example of the theory of convergent character displacement, explain Robert J.