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Functional Challenges of Tail Autotomy: Locomotor Responses to a Rapid Change in Mass and Loss of Tail Function

  • Author(s): Jagnandan, Kevin
  • Advisor(s): Higham, Timothy
  • et al.
Abstract

The ability to move effectively is critical in the survival of most animals, as locomotion plays a pivotal in prey capture, predator evasion, and other movements associated with acquiring resources and mates. However, terrestrial locomotion often requires compensation from the musculoskeletal system to overcome environmental or physiological demands. In this dissertation, I explore the demands associated with rapidly occurring changes in mass by addressing this phenomenon as a locomotor perturbation. In the leopard gecko, Eublepharis macularius, the tail accounts for 25% of the animal’s mass, which is shed almost instantaneously via autotomy in response to a perceived threat. Autotomy thus provides an effective natural model for studying the impacts of rapid mass change on locomotor mechanics and neuromuscular function. Investigations of morphology, 3D kinematics, and ground-reaction forces (GRFs) before and after autotomy in this species revealed a significant anterior shift in the animal’s center of mass (CoM) after sacrificing the tail, resulting in a shift to a more sprawled posture to preserve stability while adjusting to the change. Experimentally restricting natural undulatory movements of the tail revealed that this postural shift occurs when the tail is compromised in any way, not necessarily because of the altered mass. The tail is also suggested to be biomechanically linked to step length by rotation of the pelvic girdle and retraction of the femur, illuminating an additional source of the locomotor consequences of tail autotomy. Finally, electromyography (EMG) analyses were used to elucidate how motor control of the locomotor muscles are modulated in response to tail autotomy, revealing differential impacts in the forelimb and hind limb muscles that coincide with their locomotor functions. These results highlight the utility of tail autotomy as a system for studying the mechanical consequences of rapid mass change, the functional role of the tail, and the neuromuscular control of locomotion in response to altered demands. By understanding the functional consequences and adaptations of the locomotor system in response to tail autotomy, an evolutionary framework can be used to determine how selective pressures have shaped these responses.

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