UC Irvine

The evolution of novel locomotor modes has played a crucial role in the evolution of vertebrates. A shift in an organisms’ primary mode of locomotion or changes in the mechanical properties of the external environment require adjustments to kinematic and motor patterns. These adaptations are often associated with distinct morphological changes. Such modifications are necessary for maintaining performance in response to variation in the external physical environment. This provides the foundation for the evolution of novel modes of locomotion. Understanding this adaptability, the mechanistic, and functional implications of novel gaits and the substrates that shape biological systems can provide further insights for design parameters in synthetic and engineered systems. My dissertation seeks to understand this adaptability and the functional implications of novel gaits and substrates that affect them. I examined how the evolution of novel locomotor modes shape variation in: (Chapter 1) limb morphology, (Chapter 2) motor control strategies, and (Chapter 3) muscle properties in frogs. I used morphological, biomechanical, and physiological approaches to understand modulation of organismal locomotor patterns and responses to varying external conditions.

First, we explore how quadrupedal walking gaits are achieved in four frog species that are ancestrally specialized for jumping. We examine how the prominence of this gait correlates with a shift in limb morphology and limb posture. We find frogs specialized for walking accommodate a quadrupedal gait with an increase in relative forelimb length compared to the average anuran body plan and maintain greater vertical retraction in the hindlimb compared to the forelimb during walking. Second, I investigate the effects of substrate compliance on limb kinematics and motor control patterns of jumping Cuban tree frogs. We found evidence Cuban tree frogs use a feedforward control program and compliance substrates potentially disrupt the inertial catch mechanism used to store elastic energy. Last, I explore the effects of substrate compliance on elastic energy storage at the muscle-tendon level. We develop a spring-loaded latch analogue model using an in vitro muscle preparation. We find slower rates of energy release, less optimal latches, allow for greater energy recovery from compliant substrates.