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Fig. 9. Danio rerio mutants exclude and identify pathways for evolutionary changes in D. nigrofasciatus. Shown are selected images of representative larvae that were imaged throughout pigment pattern metamorphosis. Schematics (bottom row) illustrate the locations of early larval melanophores (brown) and metamorphic melanophores (black), as determined by the tracing of individual cells from the early larval pigment pattern into the adult pigment pattern (dorsal scale-associated melanophores are omitted for clarity). (A-D) ednrb1 mutant D. rerio develop an adult pattern of stripe and spots, superficially similar to D. nigrofasciatus (Parichy and Johnson, 2001). Nevertheless, the underlying mode of pigment pattern metamorphosis differs from D. nigrofasciatus, as few early larval melanophores contribute to the developing adult stripes. Arrow in A indicates a newly differentiated metamorphic melanophore. (E-H) puma mutant D. rerio exhibit a severe reduction in metamorphic melanophore numbers, whereas early larval melanophores (arrowheads) spread laterally over the flank, similar to D. nigrofasciatus. (I,J) picasso mutant D. rerio also have fewer metamorphic melanophores, and increased persistence of early larval melanophores (arrowheads). (M-P) Hybrids between D. rerio and D. nigrofasciatus exhibit fewer metamorphic melanophores than D. rerio, yet early larval melanophores only rarely contribute to the adult stripes (arrowheads), similar to D. rerio but unlike D. nigrofasciatus (compare with Fig. 3E,J). A few early larval melanophores at the horizontal myoseptum persist into the adult pigment pattern (as in D. rerio), but early larval melanophores along the ventral myoseptum typically do not join the developing adult ventral primary melanophore stripe (as in D. rerio, but unlike D. nigrofasciatus). (Q-T) Hybrids between puma mutant D. rerio and D. nigrofasciatus exhibit early larval melanophore behaviors similar to those seen in D. nigrofasciatus. Although a few early larval melanophores leave their initial positions in control hybrids (P'), these cells are increased in number in puma tester hybrids, particularly among melanophores in the vicinity of the anal fin (arrowheads, T). Sites of early larval melanophore stripes are indicated at the dorsal and ventral margins of the myotomes (horizontal arrowheads), and at the horizontal myoseptum (squares) in A, E, I, M and Q.

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