Advisor:  Daniel I. Goldman, Ph.D. (Georgia Institute of Technology)
Committee:  Stephen P. DeWeerth, Ph.D. (Georgia Institute of Technology / Khalifa University), David Hu, Ph.D. (Georgia Institute of Technology), T. Richard Nichols, Ph.D. (Georgia Institute of Technology) and Kurt Wiesenfeld, Ph.D. (Georgia Institute of Technology)

A diversity of animals live on and within granular media, materials that can display both solid and fluid-like features. Dry granular media, such as those found in sandy deserts, are collections of particles that interact through dissipative, repulsive contact forces; dry deserts account for more than 6% of the Earth’s surface. Wet granular media make up an even larger proportion of the planet, occurring in rainforest soils, beaches, agricultural land and even at the bottom of oceans. Despite the numerous animals that move on and within these substrates, little is known about the biomechanics and neural control strategies used to locomote effectively within these terrains.

This dissertation work will explore burial and subsurface movement strategies in dry and wet granular materials, in which animals become completely surrounded by the substrate and material properties can strongly influence animal behavior. The first aim will interrogate the neural control strategies employed during movement in dry sand using the sandfish (Scincus scincus), a lizard native to the Sahara desert.  We will use synchronized electromyogram (EMG) recordings in epaxial musculature with visible light and x-ray imaging to quantify changes in activation timing and EMG intensity with varying speed, depth and media compaction. In the second aim, kinematic analysis will be used to characterize the fast burial process used by sandfish. Specifically, the function of the limbs in rapid burial will be investigated by comparing normal burial with the burial when the limbs are restrained. In the last aim, both animal and physics experiments will be used to study the differences between locomotion in wet and dry media. Resistive forces will be quantified in granular media of varying water content and controlled compaction. In addition, the kinematics of the ocellated skink (Chalcides ocellatus), a desert generalist found in both dry arid regions and wet coastal areas, will be compared during subsurface locomotion in a wet and dry substrate. This research will aid in the discovery of basic control principles for locomotion within granular media and may lead to advances in the design of robotic devices capable of moving within these complex environments.