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Fig. 2
Iridophore development differs between D. rerio and D. nigrofasciatus.
(A) Young adult patterns of the two species, illustrating fewer melanophores of D. nigrofasciatus compared to D. rerio. Stripes and interstripes are marked at the left. 1D, 1V: primary dorsal and ventral stripes. 2V, secondary ventral stripe. I1, I2, I3: Primary, secondary and tertiary interstripes. (B) Iridophores during primary stripe and secondary interstripe formation. Shown are representative individuals imaged repeatedly for D. rerio (upper) and D. nigrofasciatus (lower), with iridophores of the primary interstripe indicated by blue arrowheads. Fish were imaged throughout adult pattern formation with stages PB through J [14] illustrated here (corresponding to days ~14 through 38 post fertilization, shown for heuristic purposes only). Insets show iridophores at higher magnification. In D. nigrofasciatus, iridophores are comparatively few, and do not as extensively populate the region of the secondary ventral stripe or the secondary ventral interstripe (blue arrow in D. rerio). Melanophores of the primary ventral stripe occur more ventrally than in D. rerio and tended to be more closely associated with vertical myosepta (marked by red asterisks). Apparent differences in melanophore sizes between species may reflect lower densities and more spread morphologies in D. nigrofasciatus compared to D. rerio [26,79]. Sample sizes (N): 9 D. rerio; 6 D. nigrofasciatus. (C) Clonally related iridophores increased in number in both species between formation of primary interstripe (left; stage PB+) and subsequent pattern reiteration (right; J++). Points connected by lines represent individuals at each developmental stage. Starting numbers were not significantly different (F1,10 = 0.94, P = 0.4), whereas final numbers were significantly fewer in D. nigrofasciatus than in D. rerio (repeated measures, species x stage interaction, F1,10 = 7.47, P<0.05; N = 5 D. rerio, N = 6 D. nigrofasciatus).