Meeting Abstract
Some animals appear to counter size-related increases in bone and muscle stress through changes in posture, with larger animals adopting an upright posture. Varanid lizards are a model system to study scaling as they exhibit a 3-fold increase in body size within a single genus, reducing phylogenentic influences. We would expect these lizards to become more upright as they increase in size, but posture does not change with body size. Instead, variations in posture are associated with habitat—arboreal species adopt a more crouched posture than terrestrial species. However, the underlying morphological basis for these differences in both posture and kinematics with habitat remains unclear. We present the first set of data of hindlimb muscle architecture, kinematics, and scaling of muscle properties in arboreal and terrestrial varanids. Architecture and masses of 12 hindlimb muscles were recorded for 15 varanids (body mass: 0.1 to 40 kg). Fascicle lengths scale with geometric similarity (M0.33) but muscle mass for thigh retractors do not scale with M1.0, but rather with a larger exponent M1.17. Terrestrial lizards have longer fascicles in the ankle flexors and extensors, likely related to the increased ankle range of motion during running in terrestrial as compared to arboreal species. Further, we collected 3D kinematics and ground reaction forces for 7 individuals running at various speeds. We look at differences in joint moments during running to determine how muscle stress changes with size and posture. Understanding the kinematic and musculoskeletal differences associated with size and posture provides valuable insight into the morphological adaptations associated with locomotor performance, size and habitat in animals.
