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Fig. 3. Pigment pattern metamorphosis differs between D. rerio
(A-E') and D. nigrofasciatus (F-J'). Panels shown are of
selected days from a complete image series for individual, representative
larvae. In A and F, the 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 D. rerio,
pigment pattern metamorphosis begins with the differentiation of pioneer
metamorphic melanophores over the ventral myotomes (A, arrow), with additional
metamorphic melanophores (B, arrow) appearing both dorsally and ventrally over
a period of several days (B-D). Adult primary stripes become evident as
dispersed melanophores migrate to sites of stripe formation and additional
metamorphic melanophores differentiate within the stripes (D,E). A few early
larval melanophores move from the horizontal myoseptum to join the adult
dorsal primary melanophore stripe (C-E, arrowheads). Near the end of pigment
pattern metamorphosis the larvae have developed an adult dorsal primary
melanophore stripe and an adult ventral primary melanophore stripe (1D, 1V,
respectively, in panel E). The adult ventral primary melanophore stripe
develops just ventral to the level of the aorta (a, in panel E), about halfway
between the horizontal myoseptum and the ventral margin of the myotomes
(E'). In D. nigrofasciatus, pigment pattern metamorphosis
begins with early larval melanophores becoming displaced from the larval
stripes (F, melanophores 1-6). Whereas some metamorphic melanophores
differentiate de novo (G,H, arrows), these are markedly fewer than in D.
rerio. As metamorphosis proceeds, melanophores initially present in the
ventral early larval stripe (H, arrowheads) become increasingly distant from
the ventral margin of the myotomes. By late stages of pigment pattern
metamorphosis, a complete adult ventral primary melanophore stripe has formed
(J), and both dorsal and ventral stripes contain numerous early larval
melanophores. The D. nigrofasciatus ventral primary melanophore
stripe develops further ventrally relative to the level of the aorta (a, J),
and closer to the ventral margin of the myotome (J'), compared to D.
rerio. Inset (J) shows brownish cast of an adult stripe melanophore (6)
that originated in the early larval stripe. (E',J') Schematics of
fish shown in E and J, showing melanophores associated with the adult primary
melanophore stripes, and residual melanophores from the early larval stripes
dorsally and ventrally, as determined by following individual melanophores
from early larval stages throughout the image series (i.e. by analyzing cell
lineage rather than by examination of final melanophore colors). For
consistency with Fig. 2,
melanophores that originated in the early larval pattern are shown in brown,
and melanophores that differentiated during metamorphosis are shown in black.
Dorsal metamorphic melanophores that will cover the dorsum and dorsal scales
are omitted for clarity. Double arrowheads in B and F indicate deep, internal
melanophores that are ventral to the notochord, or dorsal to the neural tube,
respectively, and that do not contribute to pigment patterns beneath the skin.
Standard lengths of larvae (mm): A, 6.7; B, 7.4; C, 8.6; D, 10.3; E, 11.5; F,
6.7; G, 7.1; H, 8.6; I, 9.4; J, 10.3.
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