Pentadactyl pattern of the avian wing autopodium and pyramid reduction hypothesis
Article first published online: 23 JUL 2002
Copyright © 2002 Wiley-Liss, Inc.
Journal of Experimental Zoology
Volume 294, Issue 2, pages 152–159, 15 August 2002
How to Cite
KundráT, M., Seichert, V., Russell, A. P. and Smetana, K. (2002), Pentadactyl pattern of the avian wing autopodium and pyramid reduction hypothesis. J. Exp. Zool., 294: 152–159. doi: 10.1002/jez.10140
- Issue published online: 26 DEC 2002
- Article first published online: 23 JUL 2002
- Manuscript Accepted: 1 MAY 2002
- Manuscript Received: 15 APR 2002
- Granting Agency of Charles University in Prague, Czech Republic. Grant Number: 136/2000/B BIO/ PřF
- Ministry of Education, Youth and Sport of the Czech Republic. Grant Number: MSM 111100005
- Natural Sciences and Engineering Research Council of Canada. Grant Number: OGP0009745
We report herein that a pentadactyl developmental pattern is evident in early wing morphogenesis of Gallus (chicken) and Struthio (ostrich). Five avascular zones (spatially predestined locations of contiguous metacarpal and phalangeal aggregation) and four interdigital vascular spaces are established by the regression patterns of autopodial vasculature. Transient vestiges of the first and fifth metacarpals are confirmed histologically and histochemically. They lie within the preaxial-most and postaxial-most avascular zones, respectively. These observations reveal conservative patterning of the avian hand and corroborate a II-III-IV metacarpal interpretation, argue for II-III-IV identity of ossified digits in birds, and favour a simple reduction rather than a homeotic shift in terms of the phenotype expressed by Hox genes in the phylogeny of the avian manus. We suggest that gradual, bilateral reduction of phalanges and metacarpals, via apoptosis mediated by BMP, occurred during the evolution of birds (Pyramid Reduction Hypothesis). This is congruent with the establishment of a central wing axis that became co-opted for coordinated movements. On the basis of evidence presented here, the direct avian ancestor is predicted to have been five-fingered with dominant digits (+ metacarpals) as follow: II, III, IV. J. Exp. Zool. (Mol. Dev. Evol.) 294:152–159, 2002. © 2002 Wiley-Liss, Inc.