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Vol. 97, Issue 1, 212-216, January 4, 2000
Department of Ecology and Evolutionary Biology, Yale University,
165 Prospect Street, New Haven, CT 06511
Communicated by Francis H. Ruddle, Yale University, New Haven,
CT, November 1, 1999 (received for review March 2, 1999)
Heterochrony, the relative change of developmental timing, is one
of the major modes of macroevolutionary change; it identifies temporally disassociated units of developmental evolution. Here, we
report the results of a fine-scale temporal study for the expression of
the developmental gene hairy and morphological
development in three species of Drosophila, D.
melanogaster, D. simulans, and D.
pseudoobscura. The results suggest that between and among closely related species, temporal displacement of ontogenetic trajectory is detected even at the earliest stage of development. Overall, D. simulans shows the earliest expression,
followed by D. melanogaster, and then by D.
pseudoobscura. Setting D. melanogaster as the
standard, we find the approximate time to full expression is
accelerated by 13 min, 48 s in D. simulans and
retarded by 24 min in D. pseudoobscura. Morphologically,
again with D. melanogaster setting the standard,
initiation of cellularization is faster in D. simulans
by 15 min, 42 s; and initiation of morphogenesis is faster in
D. simulans by 18 min, 7 s. These results seem to be consistent with the finding that the approximate time to full expression of hairy is accelerated by 13 min, 48 s
in D. simulans. On the other hand, the same
morphological events are delayed by 5 min, 32 s, and by 11 min,
32 s, respectively, in D. pseudoobscura. These
delays are small, compared with the 24-min delay in full expression.
The timing changes, in total, seem consistent with continuous phyletic
evolution of temporal trajectories. Finally, we speculate that
epigenetic interactions of hairy expression timing and
cell-cycle timing may have led to morphological differences in the
terminal system of the larvae.
Evolution
Molecular heterochrony in the early development
of Drosophila
*
To whom reprint requests should be addressed. E-mail:
junhyong.kim{at}yale.edu.
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