Vortex arrays and chaotic mixing by swimming invertebrate larvae - Gilpin, William Carl; Prakash, Manu; Dabiri, John O. (John Oluseun); Greenleaf, William James; Stanford University, Department of Applied Physics ([Stanford, California] : [Stanford University], 2019)
The first animals evolved in the oceans, which formed the context for evolutionary innovations spanning from the first specialized locomotory appendages, to the first nervous systems. Fluid dynamical constraints thus provide insight into biomechanical adaptations in early animals, illustrating how physical forces shaped the diversity of early body plans and life history strategies. This thesis seeks to bridge the existing body of work on the locomotion of microorganisms at low Reynolds numbers, with broader questions related to the origin of multicellularity and the invertebrate nervous systems. First, I review the existing literature on the biophysics of cilia and flagella, the fundamental cellular organelles that enable locomotion at low Reynolds numbers. This review specially focuses on the different modeling paradigms that apply across scales---from singularity-type hydrodynamic models describing single flagella, to topological models describing large ensembles of interacting cilia. Next, I describe a new type of cilia-driven swimming behavior that we recently observed in starfish larvae. This swimming gait involves the formation of dense vortex arrays around the swimming animal, which we find entrain and capture edible algae, the animals' primary food source. I describe how this adaptation is novel among known low-Reynolds number swimmers, and how it is enabled by the larvae's unique ability to control its cilia using its nervous system. Next, I discuss more broadly the appearance and role of neuronally-controlled ciliary bands in the swimming behavior of invertebrates. I highlight an unusual behavioral phenomenon occurring in many invertebrates, wherein the animal periodically and rapidly modulates its global ciliary beat pattern, producing substantial changes in the the larval flow field. Using a combination of hydrodynamic experiments and theoretical models, I show that these modulations are sufficient to induce strong chaotic mixing of the local flow field, further enhancing the organism's feeding rate.
Submitted to the Department of Applied Physics.
Thesis Ph.D. Stanford University 2019.
Rights: (c) Copyright 2019 by William Carl Gilpin
Rights: This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
Keywords: theses; text