Meeting Abstract
12.2 Sunday, Jan. 4 Molecular evidence of a digit identity frameshift in the Italian Three-toed Skink (Chalcides chalcides) YOUNG, R. L.*; CAPUTO, V.; GIOVANNOTTI, M.; KOHLSDORF, T.; WAGNER, G. P.; Yale University; University of Ancona; University of Ancona; Yale University; Yale University rebecca.youngbrim@yale.edu
While modifications of trait development are required for evolutionary change in phenotypes, evolutionary persistence of phenotypes across taxa does not require maintenance of developmental pathways. Several studies of digit reduction exemplify this phenomenon by calling into question the homology of the remaining digits. In birds, the debate results from a conflict between embryological and anatomical evidence of digit identity. The avian hand contains three digits. Morphologically the digits resemble ancestral digits I, II, and III; however, embryological data reveals that these structures develop from digit condensations II, III, and IV. Extensive investigations of developmental and molecular mechanisms of digit formation in the avian hand have resolved this conflict by providing evidence of a digit identity frameshift during development. In this case, the properties of development critical for generating digits I, II, and III are shifted onto digit condensations II, III, and IV. In the Italian Three-toed Skink (Chalcides chalcides), a similar conflict between anatomical and embryological evidence of digit homology has been described. Here we ask whether the same mechanism, a homeotic frameshift in digit identity, can resolve the conflict between the developmental origins and adult morphology of digits in both the fore- and hindlimb of Chalcides chalcides. We first detail the anatomical and embryological evidence of digit homology in this system. Second, we examine expression patterns of posterior HoxD genes with known expression and function in digit identity determination. Finally, we discuss the implications of our findings for the role of the frameshift as a mechanism of dissociation of character identity and morphology and the importance of this mechanism for character evolution.
