The relative contributions of multiarticular snake muscles to movement in different planes
Project
ID: 000495574
Public
Tingle, J.L., D.J. Jurestovsky, and H.C. Astley. 2030. The relative contributions of multiarticular snake muscles to movement in different planes. Journal of Morphology. Muscles spanning multiple joints play important functional roles in a wide range of systems across tetrapods; however, their fundamental mechanics are poorly understood, particularly the consequences of anatomical position on mechanical advantage. Snakes provide an excellent study system for advancing this topic. They rely on the axial muscles for many activities, including striking, constriction, defensive displays, and locomotion. Moreover, those muscles span from one or a few vertebrae to over 30, and anatomy varies among muscles and among species. We characterized the anatomy of major epaxial muscles in a size series of corn snakes (Pantherophis guttatus) using diceCT scans, and then took several approaches to calculating contributions of each muscle to force and motion generated during body bending, starting from a highly simplistic model and moving to increasingly complex and realistic models. Only the most realistic model yielded equations that included the consequence of muscle span on torque-displacement trade-offs, as well as resolving ambiguities that arose from simpler models. Next, we used an ANCOVA to test whether muscle cross-sectional areas or lever arms (total magnitude or pitch/yaw/roll components) were significantly related to snake mass, longitudinal body region (anterior, middle, posterior), and/or muscle group (semispinalis-spinalis, multifidus, longissimus dorsi, iliocostalis, levator costae). Finally, we examined whether vertebral length, muscle cross-sectional areas, and lever arms scaled with geometric similarity (isometry) or allometrically. Our results contribute to knowledge of snake muscles specifically and multiarticular muscle systems generally, providing a foundation for future comparisons across species and bioinspired multiarticular systems.