24.2 Wednesday, Jan. 4 Regional Variation in the Dynamic Mechanical Properties of Shark Vertebral Columns PORTER, M.E.*; DIAZ, C; LONG, J.H. Jr; Vassar College; Vassar College; Vassar College email@example.com
In swimming fishes, body curvature varies among species, individuals, and even within an individual depending on anatomical position and swimming speed. The magnitude and pattern of body curvature of the axial midline is thought to be a function of the stiffness of the body and the vertebral column.. Our goal was to examine body stiffness, and other dynamic mechanical properties, of the vertebral column along the length of the body in two conspecific, but phylogenetically distant, shark species, Squalus acanthias and Mustelus canis. We used a customized rig on dynamic testing machine (MTS Tytron 250) to translate single axis movement into bending. We tested segments of ten centra over a range of frequencies and curvatures, similar to those experienced by these species when swimming, in an environmental chamber. We measured the apparent composite modulus, E (in Pa), which is an estimate of structural stiffness or the resistance, at a material level, to imposed motions. E was calculated using the applied bending curvature and the bending moments that result. There are clear differences, in both species, between the E of the vertebral column in precaudal and caudal regions: the caudal region is much stiffer. These data suggest that the caudal region, compared to the precaudal region, stores and releases more elastic spring energy during swimming. We hypothesize that since this pattern occurs in two phylogenetically-distant species, these regional differences in vertebral column function may be a general solution for thrust production in sharks. This work was supported by NSF IOS-0922605.