| dc.description.abstract | Digit identity in the avian wing is a classical
example of conflicting anatomical and embryological evidence
regarding digit homology. Anatomical in conjunction with
phylogenetic evidence supports the hypothesis that the three
remaining digits in the bird wing are digits 1, 2, and 3. At the
same time, various lines of embryological evidence support the
notion that these digits develop in positions that normally
produce digits 2, 3, and 4. In recent years, gene expression as
well as experimental evidence was published that supports the
hypothesis that this discrepancy arose from a digit identity shift
in the evolution of the bird wing. A similar but less well-known
controversy has been ongoing since the late 19th century
regarding the identity of the digits of the three-toed Italian skink,
Chalcides chalcides. Comparative anatomy identifies these
digits as 1, 2, and 3, while embryological evidence suggests
their derivation from embryological positions 2, 3, and 4. Here
we re-examine this evidence and add gene expression data to
determine the identity of the three digits of C. chalcides. The
data confirm that the adult and the embryological evidence for
digit identity are in conflict, and the expression of Hoxd11
suggests that digits 1, 2, and 3 develop in positions 2, 3, and 4.
We conclude that in C. chalcides, and likely in its close
relatives, a digit identity frame shift has occurred, similar to the
one in avian evolution. This result suggests that changes in of
digit identity might be a more frequent consequence of digit
reduction than previously assumed. | |
