Meeting Abstract

P3.157  Monday, Jan. 6 15:30  Head Stability During Walking in Alligator mississippiensis GEORGI, JA*; MANFREDI, KR; Midwestern University, Glendale; Midwestern University, Glendale jgeorgi@midwestern.edu

Increasingly more studies are addressing the connection between locomotion and the semicircular ducts. However, the relationship between these organs that sense the rotational movement of the head and locomotion is indirect. During most locomotion, movement of the head is mediated by the neck, trunk, and limbs. It is, therefore, critical to understand the patterns of head movement during locomotion. We used 3D motion capture on 8 walking American alligators (Alligator mississippiensis) ranging in total length from 0.92 to 1.58 m, and compared these data to previously reported data for African spurred tortoises (Geochelone sulcata). In alligators, as in tortoises, the length of the stride increases with body size (p = 0.005). In contrast to tortoises, alligators showed increases in stride duration (p = 0.028) and duty factor (p=0.031) with increasing body size. In tortoises, head instability increases with stride speed, but those increases are inversely proportional to body size with smaller increases in larger tortoises. Although there is also an increase in head instability in alligator (n = 5), this relationship is constant across body sizes (SMA slope comparison p = 0.478). In addition, the increase in head instability at higher stride speed (SMA slope = 0.069) is much smaller than that for even the largest tortoise (SMA slope = 0.208). These data show broad scale differences in movements of the head in response to limb-based locomotion between vertebrate taxa. This supports the growing evidence that semicircular duct morphology may be adapted to different types of locomotion. Whether the changes in head stability simply relate to the ontogenetic differences in step cycle or whether there is a significant component of semicircular duct control is not addressed by this study and remains to be investigated.