Meeting Abstract

P3.128  Thursday, Jan. 6  The Vertebral Column of Sharks: Regional Variation in Dynamic Mechanical Properties and Locomotor Function DIAZ, C.*; LONG, J.H.; PORTER, M.E.; Vassar College; Vassar College; Vassar College cadiaz@vassar.edu

The mechanical behavior of any structural system can be understood by the following approach: (1) measure how the structure is loaded during operation, (2) analyze the structure’s geometry and the arrangement of its structural elements, and (3) the mechanical properties of its elements. Our goal was to apply this integrated approach to the understanding the mechanical behavior of the vertebral columns of sharks. First, we measured the motion of the vertebral column in swimming and turning sharks. Second, we used those kinematic inputs to measure the apparent composite modulus, E (in Pa), of 10 segment sections of vertebral columns from two species of sharks, Squalus acanthias and Mustelus canis. The E of a structure is an estimate of stiffness, the resistance, at a material level, to imposed motions and is calculated using the applied bending curvature and the resisting bending moments that result. Using a customized bending rig on a single-axis dynamic testing machine (MTS Tytron 250), precaudal and caudal vertebral segments were bent over a range of frequencies and curvatures in an environmental chamber. The most dramatic finding was the clear difference, in both species, between the E of the vertebral column in precaudal and caudal regions. The caudal region is much stiffer, suggesting that, compared to the precaudal region, it stores and releases more elastic spring energy during swimming. The fact that this pattern occurs in two phylogenetically-distant species suggests that regional differences in the function of the vertebral column may be a general solution to the problem of thrust production in sharks. This work was supported by NSF DBI-0442269 and IOS-0922605.