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recent papers on digit homology
don't recall seeing these papers being cited on the DML (might be wrong
though, especially about the last one, which is from the january issue).
J Exp Zoolog B Mol Dev Evol. 2005 May 15;304(3)
"Hox genes, digit identities and the theropod/bird transition"
Frietson Galis 1 *, Martin Kundrát 2, Johan A.J. Metz 1 3
Vargas and Fallon (2005. J Exp Zool (Mol Dev Evol) 304B:86-90) propose that Hox
gene expression patterns indicate that the most anterior digit in bird wings is
homologous to digit 1 rather than to digit 2 in other amniotes. This
interpretation is based on the presence of Hoxd13 expression in combination
with the absence of Hoxd12 expression in the second digit condensation from
which this digit develops (the first condensation is transiently present). This
is a pattern that is similar to that in the developing digit 1 of the chicken
foot and the mouse hand and foot. They have tested this new hypothesis by
analysing Hoxd12 and Hoxd13 expression patterns in two polydactylous chicken
mutants, Silkie and talpid2. They conclude that the data support the notion
that the most anterior remaining digit of the bird wing is homologous to digit
1 in other amniotes either in a standard phylogenetic sense, or alternatively
in a (limited) developmental sense in agreement with the Frameshift
Hypothesis of Wagner and Gautier (1999, i.e., that the developmental pathway
is homologous to the one that leads to a digit 1 identity in other amniotes,
although it occurs in the second instead of the first digit condensation). We
argue that the Hoxd12 and Hoxd13 expression patterns found for these and other
limb mutants do not allow distinguishing between the hypothesis of Vargas and
Fallon (2005. J Exp Zool (Mol Dev Evol) 304B:86-90) and the alternative one,
i.e., the most anterior digit in bird wings is homologous to digit 2 in other
amniotes, in a phylogenetic or developmental sense. Therefore, at the moment
the data on limb mutants does not present a challenge to the hypothesis, based
on other developmental data (Holmgren, 1955. Acta Zool 36:243-328; Hinchliffe,
1984. In: Hecht M, Ostrom JH, Viohl G, Wellnhofer P, editors. The beginnings of
birds. Eichstätt: Freunde des Jura-Museum. p 141-147; Burke and Feduccia, 1997.
Science 278:666-668; Kundrát et al., 2002. J Exp Zool (Mol
Dev Evol) 294B:151-159; Larsson and Wagner, 2002. !
J Exp Zool (Mol Dev Evol) 294B:146-151; Feduccia and Nowicki, 2002.
Naturwissenschaften 89:391-393), that the digits of bird wings are homologous
to digits 2,3,4 in amniotes. We recommend further testing of the hypothesis by
comparing Hoxd expression patterns in different taxa. J. Exp. Zool. (Mol. Dev.
Evol.) 304B:198-205. 2005
"The digits of the wing of birds are 1, 2, and 3. a review "
Alexander O. Vargas 1 2 *, John F. Fallon 3
Fossil evidence documenting the evolutionary transition from theropod dinosaurs
to birds indicates unambiguously that the digits of the wing of birds are
digits 1, 2, and 3. However, some embryological evidence suggests that these
digits are 2, 3, and 4. This apparent lack of correspondence has been described
as the greatest challenge to the widely accepted theropod-bird link (Zhou 2004.
Naturwissenschaften 91:455-471). Here we review the pertinent literature
regarding the debate on the origin of birds and wing digital identity and the
evidence in favor of a 1, 2, 3 identity of the wing digits. Recent molecular
evidence shows that the expression of Hoxd12 and Hoxd13 in the developing wing
supports the theropod-bird link. In the chicken foot and in the mouse hand and
foot, digit 1 is the only digit to combine the expression of Hoxd13 with the
absence of expression of Hoxd12. The same is observed in the anterior digit of
the wing, suggesting it is a digit 1, as expected for a theropod.
Nevertheless, Galis et al. (2005. J Exp Zool (Mol Dev Evol) in press), argue
that Hoxd12 and Hoxd13 expression patterns in mutant limbs do not allow
distinguishing the most anterior digit in the bird wing from digit 2. They also
argue that constraints to the evolution of limb development support the 2, 3, 4
identity of the wing digits. However, the case put forward by Galis et al. is
biased and flawed with regard to interpretation of mutant limbs, developmental
mechanisms, stages observed, and the description of the evolutionary variation
of limb development. Importantly, Galis et al. do not present evidence from
wild-type limbs that counters the conclusions of Vargas and Fallon (2005. J Exp
Zool (Mol Dev Evol) 304B(1):85-89), and fail to provide molecular evidence to
specifically support the hypothesis that the wing digits are 2, 3, and 4. The
expression of Hoxd12 and Hoxd13 in the developing wing is consistent with the
hypothesis that birds are living dinosaurs; this view can lead
to a greater understanding of the actual l!
imits to the evolutionary variation of limb development. J. Exp. Zool. (Mol.
Dev. Evol.) 304B:206-219, 2005
J Exp Zoolog B Mol Dev Evol. 2005 Jan 15;304(1)
"Birds have dinosaur wings: The molecular evidence.
Vargas AO, Fallon JF".
Within developmental biology, the digits of the wing of birds are considered on
embryological grounds to be digits 2, 3 and 4. In contrast, within
paleontology, wing digits are named 1, 2, 3 as a result of phylogenetic
analysis of fossil taxa indicating that birds descended from theropod dinosaurs
that had lost digits 4 and 5. It has been argued that the development of the
wing does not support the conclusion that birds are theropods, and that birds
must have descended from ancestors that had lost digits 1 and 5. Here we use
highly conserved gene expression patterns in the developing limbs of mouse and
chicken, including the chicken talpid(2)mutant and polydactylous Silkie breed
(Silkie mutant), to aid the assessment of digital identity in the wing. Digit 1
in developing limbs does not express Hoxd12, but expresses Hoxd13. All other
digits express both Hoxd12and Hoxd13. We found this signature expression
pattern identifies the anteriormost digit of the wing as digit 1, in accordance
with the hypothesis these digits are 1, 2 and 3, as in theropod dinosaurs. Our
evidence contradicts the long-standing argument that the development of the
wing does not support the hypothesis that birds are living dinosaurs.
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