Meeting Abstract
Locomotor performance is fundamental to the ability of many vertebrates to survive and reproduce. Evolutionary changes in the attachments of a muscle can change its line of action, potentially altering its effectiveness in contributing to particular motions and overall locomotor performance. In cryptodire turtles, the hind limb muscles originate on the pelvis before inserting on the limb. In pleurodire turtles, derived fusion of the pelvis to the shell has caused the origins of many hind limb muscles to shift from the pelvis to the shell. To test the locomotor effects of these rearrangements, we measured hind limb kinematics, muscle moment arms, and muscle activity (EMGs), for representative aquatic generalist species of pleurodire (Emydura subglobosa) and cryptodire (Trachemys scripta) turtles in walking and swimming. We found that the hind limb muscles in pleurodires exhibited relatively greater mechanical advantage than those in cryptodires, primarily in abduction and adduction. Among muscles with different attachment locations between lineages, some (e.g., flexor tibialis internus) maintained similar activity patterns between taxa. However, other muscles showed differences in activity. For example, puboischiofemoralis internus (PIFI), which cryptodires use to protract the hip, exhibited a novel burst during stance in walking pleurodires. Due to the ventral shift of the origin of PIFI, we suspect this novel burst may stabilize or adduct the limb. Matching this prediction, pleurodires show greater hind limb adduction than cryptodires during both behaviors. Altogether, our results suggest that changes in attachment location can lead to changes in muscle activity, but such changes are not necessarily linked.
