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Fig 1 Top, Striped pattern of D. rerio showing primary (1°) light interstripe with primary dark stripes dorsally and ventrally. Secondary and tertiary interstripes and stripes are indicated only ventrally. Right, Cells that comprise dark and light pattern elements. Lighting has been adjusted to highlight or eliminate the iridescence of iridophores, and pigment cells are shown both in their natural state and after treatment with epinephrine (epi), which contracts pigment granules of melanophores and xanthophores towards cell centers. Insets at far right show higher magnification views of boxed regions. Dark stripes comprise melanophores with black melanin granules as well as more superficial iridophores that have a bluish iridescence owing to precisely oriented stacks of guanine-containing reflecting platelets (upper insets). Interstripes and interspot regions contain densely packed iridophores with a yellowish hue owing to disordered stacks of reflecting platelets, as well as more superficially located xanthophores, marked by lipid droplets containing yellow–orange carotenoids [6,54]. Middle and Bottom, Striped and spotted patterns of D. quagga and D. kyathit. Cell types present in each species were indistinguishable from those of D. rerio. In older D. kyathit and D. quagga, red pigment cells—erythrophores—were present and especially prominent in males, whereas D. quagga developed fissures and other disruptions in their stripes, especially in females (S1 Fig). Neither of these features occurs in D. rerio and we do not consider them further in this study. Scale bars, 2 mm (left) and 200 μm (right).