Biological Physics of Collective Motion: Circular Milling in Symsagittifera roscoffensis and Related Questions of Self-Organisation
type: CreativeWork
description: Collective motion, a phenomenon resulting from the interactions of many individuals, occurs across the natural world across all length scales, from the flocking of birds to the swirling of Bacillus subtilis bacteria. Understanding these phenomena is critical to understanding how the organism thrives in its chosen ecological niche. In this dissertation, we aim to identify the physical processes behind these phenomena, integrating experimental studies with accompanying theoretical models for organisms in a wide range of different taxa, and thus elucidate how they give the organism a competitive advantage in their ecosystem. Circular Milling in Symsagittifera roscoffensis. It has been observed that the plant-animal worm Symsagittifera roscoffensis exhibits circular milling behaviour, a stunning manifestation of collective motion, both naturally in rivulets on intertidal sand and in a shallow layer of sea water in a Petri dish. In the first part of this dissertation, we investigate this phenomenon, through experiment and theory, from a fluid dynamical viewpoint, focusing on the effect that an established circular mill has on the surrounding fluid. The induced fluid velocity field allows nutrient circulation as well as providing an efficient method of dispersal of waste products away from the main body of worms. A series of novel mathematical models are analyzed to understand how the flow field produced by a single worm contributes to the total flow field generated by a circular mill, in light of the particular boundary conditions that hold for flow in a Petri dish. In particular, a model that treats a circular mill as a rigid rotating disc that generates a Stokes flow is shown to capture basic experimental results very well, both in terms of the mill centre orbit direction but also the predicted streamlines. Utilising this understanding, we shed light on the fluid dynamical stability of circular mills. Secondary circular mills form around stagnation points of the flow. …
abstract: Collective motion, a phenomenon resulting from the interactions of many individuals, occurs across the natural world across all length scales, from the flocking of birds to the swirling of Bacillus subtilis bacteria. Understanding these phenomena is critical to understanding how the organism thrives in its chosen ecological niche. In this dissertation, we aim to identify the physical processes behind these phenomena, integrating experimental studies with accompanying theoretical models for organisms in a wide range of different taxa, and thus elucidate how they give the organism a competitive advantage in their ecosystem. Circular Milling in Symsagittifera roscoffensis. It has been observed that the plant-animal worm Symsagittifera roscoffensis exhibits circular milling behaviour, a stunning manifestation of collective motion, both naturally in rivulets on intertidal sand and in a shallow layer of sea water in a Petri dish. In the first part of this dissertation, we investigate this phenomenon, through experiment and theory, from a fluid dynamical viewpoint, focusing on the effect that an established circular mill has on the surrounding fluid. The induced fluid velocity field allows nutrient circulation as well as providing an efficient method of dispersal of waste products away from the main body of worms. A series of novel mathematical models are analyzed to understand how the flow field produced by a single worm contributes to the total flow field generated by a circular mill, in light of the particular boundary conditions that hold for flow in a Petri dish. In particular, a model that treats a circular mill as a rigid rotating disc that generates a Stokes flow is shown to capture basic experimental results very well, both in terms of the mill centre orbit direction but also the predicted streamlines. Utilising this understanding, we shed light on the fluid dynamical stability of circular mills. Secondary circular mills form around stagnation points of the flow. …
author: Fortune, George
language: eng
keywords: Biological Physics, Fluid Dynamics, Collective Motion, Active Matter
license: https://www.rioxx.net/licenses/all-rights-reserved/
date published: 2022-02-01
date modified: 2026-07-22T22:24:17Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.88334