Department of Anthropology, University of Texas at Austin
Thursday 11:15-11:30, Ballroom B
The semicircular canals detect head rotations and trigger compensatory movements that stabilize gaze and prevent blurring of images on the retina. Precise gaze stabilization is presumably of greater importance in animals with large eyes because loss of visual resolution will begin at a lower threshold of uncompensated motion in species with high visual acuity. Semicircular canals with larger radii are more sensitive to angular accelerations and are therefore theoretically capable of providing the vestibular feedback necessary to stabilize gaze more precisely in large-eyed species. Nevertheless, the relationship between eye size and semicircular canal sensitivity has not been examined in a comparative context.
We collected data on semicircular canal mean radius of curvature (R) and axial eye diameter (AD) for 110 species across twelve mammalian orders to evaluate the relationship between semicircular canal size and eye size. PGLS analyses show that animals with larger eyes also tend to have larger semicircular canals (p<0.001; r2=0.58). Though both variables are independently significantly correlated with body mass, the relationship between AD and R remains highly significant when the effects of body mass are accounted for using both PGLS multiple regression (p<0.001; partial r2AD= 0.30) and phylogenetically informed partial regressions (p< 0.001).
These results suggest that a significant portion of the interspecific variation in semicircular canal size among mammals is attributable to increased need for precise gaze stabilization in species with large eyes and acute vision. Evolutionary increases in eye size may therefore create selective pressure favoring concomitant increases in semicircular canal sensitivity.