Meeting Abstract

P1.167  Sunday, Jan. 4  Modularity and Integration of the Stapes: analysis of variation in the guinea pig SWIDERSKI, D.L.*; BASU, I.; ZELDITCH, M.L.; Univ. of Michigan; Univ. of Michigan; Univ. of Michigan dlswider@umich.edu

Like other model systems analyzed in studies of modularity and integration, the stapes has a complex developmental history: three ossification centers form in the cartilage of the second branchial arch, which fuses to the wall of the otic capsule, and is also excavated by the stapedial artery. Unlike those other models, the stapes has but one simple function: the transmission of sound as it is driven forcefully into the fluid-filled inner ear. Thus, the goal of our study was to determine whether variation in stapedial shape reflects the modularity of development or the integration of function. We collected stapes from adult guinea pigs that had been the subjects of unrelated surgical experiments, and quantified shape geometrically, using landmarks at discrete anatomical loci and semilandmarks outlining the crura and footplate (the legs of the arch and the elliptical saucer it stands in). Preliminary results indicate that the outer edges of the crura are more variable than the inner margins of the arterial foramen, and that the feet of the crura are more variable than the head of the stapes. The long axis of the footplate appears to be proportional to height of the arch, but its width and depth are independent. These results suggest that stapes shape is not highly integrated despite the apparent simplicity of its functional role.