1Present address: Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
Frame-shifts of digit identity in bird evolution and Cyclopamine-treated wings
Version of Record online: 24 FEB 2009
© 2009 The Author(s). Journal compilation © 2009 Wiley Periodicals, Inc.
Evolution & Development
Volume 11, Issue 2, pages 163–169, March/April 2009
How to Cite
Vargas, A. O. and Wagner, G. P. (2009), Frame-shifts of digit identity in bird evolution and Cyclopamine-treated wings. Evolution & Development, 11: 163–169. doi: 10.1111/j.1525-142X.2009.00317.x
- Issue online: 24 FEB 2009
- Version of Record online: 24 FEB 2009
SUMMARY A highly conserved spatio-temporal pattern of cartilage formation reveals that the digits of the bird wing develop from positions that become digits 2, 3, and 4 in other amniotes. However, the morphology of the digits of early birds like Archaeopteryx corresponds to that of digits 1, 2, and 3 of other archosaurs. A hypothesis is that a homeotic “frame-shift” occurred, such that in the bird wing, digits 1, 2, and 3 develop from the embryological positions of digits 2, 3, and 4. Experimental homeotic transformations of single digits are well-documented, but frame-shifts of more than one digit are not. We investigated the pattern of cartilage formation in the development of Cyclopamine-treated wings. When Cyclopamine was applied between stages 18 and 21, morphologies that normally develop from positions 2 and 3 developed from positions 3 and 4. The serial shift of digit identity toward posterior confirms a mechanistic possibility that was previously inferred from the evolutionary history of birds.