Book Description

The physics of behavior is a rapidly growing discipline which seeks simple descriptions of an animal's behavior in the language of low dimensional dynamical systems constructed from data driven approaches. Despite rapid progress, we still do not generally understand the rules which shape these emergent behavioral manifolds in the face of complicated neuro-construction -- even in the simplest of animals. In this work, we introduce a non-neuromuscular model system which is complex enough to teach us something new but also simple enough for us to understand deeply: Trichoplax Adhaerens. Through the study of this experimental model, we stand to learn more about how the animal kingdom builds successful animals from millions of specialized cells. Central to this work, we report five experimental discoveries: 1. a broad crossover regime between swimming and stalling in ciliary oscillators interacting with a surface via an adhesion energy which we call 'ciliary walking', 2. sub-second ciliary reorientations can self-organize into a collective phenomena which we call 'ciliary flocking', 3. the dominant behavioral manifold of ciliary flocking is shaped by a stable emergent coherent structure topologically classified as a +1 defect, 4. the top layer of the organism exhibits ultrafast cellular contractions which can reduce the cellular cross section by 50\% in a single second generating nonlinear contraction waves, and 5. the bottom tissue of the organism mixes different cell types to tune the material response introducing the concept of an 'epithelial alloy'. We complement these discoveries with a suite of models by construction at every scale of the problem from organelle to organism. Through a careful study of these frameworks of many-body dynamical systems driven out-of-equilibrium by distributed activity, we report an array of conceptual tools (excitable mechanics of spatio-temporal fields, active-elastic parametric resonance, and an inverse energy cascade) which enable these non-neuromuscular animals to perform agile locomotion across millions of cells without a central controller. We hope these results can inspire future approaches to technologies which exploit distributed agency such as swarm robotics and edge computing. Looking ahead, we suggest that the simple perception-actions cycles of this organism provide a promising opportunity to study the morphological computation embedded in this physical reservoir of high-dimensional, nonlinear tissue dynamics.