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Fig. 4 duox requirement for the timing of color pattern formation in zebrafish. (A) Graph representing T3 level (in pg of T3 normalized by the weight of the fish in g) in A. percula new recruits sampled in H. magnifica or S. gigantea (nonparametric Mann–Whitney U test, P = 0.0022). (B) Volcano plot of differentially expressed genes between A. percula new recruits living in H. magnifica or S. gigantea. Positive Log2FC values correspond to an increased expression in recruits from S. gigantea, while negative Log2FC corresponds to increased expression in recruits from H. magnifica. The blue and yellow points correspond to significantly differentially expressed genes. The vertical black lines delimit the Log2FC threshold of 1, while the horizontal line corresponds to the corrected P threshold. (C) Inverted fluorescence images show iridophores (dark cells) marked by pnp4a:mem-mCherry expression at 10.6-mm SL in wild-type (Left) and duox CRISPR/Cas9 mutants of zebrafish D. rerio (Right). (D) Numbers of interstripes were scored qualitatively over SL in wild-type (blue, n = 61) and duox CRISPR/Cas9 zebrafish mutants (yellow, n = 51). Complete interstripes received a score of 1 and developing interstripes received a score of 0.5. Each circle represents a single individual and points are jittered vertically for clarity, and equivalently smoothed splines are shown for ease of visualization. The differences in total numbers of interstripes and tractories of interstripe addition resulted in significant effects of genotype (likelihood ratio test, χ2 = 91.7, P < 0.0001, degrees of freedom [d.f.] = 1) and genotype × SL interaction (χ2 = 21.9, P < 0.0001, d.f. = 1). (E) Despite having fewer interstripes overall, duox-deficient zebrafish had proportionally more of the flank covered by dense, interstripe iridophores as compared to the wild type (F1,43 = 76.1, P < 0.0001). The bars indicate means ± 95% CIs (scale bar in A, 200 µm).