The emergence and transient behaviour of collective motion in active filament systems

Ryo Suzuki,Andreas R Bausch

doi:10.1038/s41467-017-00035-3

Abstract

Most living systems, ranging from animal flocks, self-motile microorganisms to the cytoskeleton rely on self-organization processes to perform their own specific function. Despite its importance, the general understanding of how individual active constituents initiate the intriguing pattern formation phenomena on all these different length scales still remains elusive. Here, using a high density actomyosin motility assay system, we show that the observed collective motion arises from a seeding process driven by enhanced acute angle collisions. Once a critical size is reached, the clusters coarsen into high and low density phases each with fixed filament concentrations. The steady state is defined by a balance of collision induced randomization and alignment effects of the filaments by multi-filament collisions within ordered clusters.

Highlights

Most living systems, ranging from animal flocks, self-motile microorganisms to the cytoskeleton rely on self-organization processes to perform their own specific function
Active systems show a plethora of intriguing spatio-temporal patterns, a remarkable self-organizing process that exhibits structures ranging from cooperative animal group motion[1, 2] to as diverse as swarming microorganisms[3,4,5] or aster-like structures in cytoskeletal systems[6, 7]
The transition is driven by the emergence of seeds as quantified by the effective binary collision statistics in a system above the critical transition concentration but in a disordered state that is seen well before the time point where polar order structures appear

Summary

Introduction

Most living systems, ranging from animal flocks, self-motile microorganisms to the cytoskeleton rely on self-organization processes to perform their own specific function. To understand the origins of such fascinating structures, theoretical approaches ranging from micro- and mesoscopic studies[8,9,10,11,12,13,14] to hydrodynamic descriptions[15,16,17,18,19,20] have been developed They have been followed by experimental studies in reconstituted[21,22,23,24,25] and synthetic[26,27,28,29,30] systems. The transition is driven by the emergence of seeds as quantified by the effective binary collision statistics in a system above the critical transition concentration but in a disordered state that is seen well before the time point where polar order structures appear. We identify the self-amplification of the weak effect of the binary collisions at acute angles along with the resulting increased number of collisions at all angles to be the contributing factors that enable the order transition in the active filament system

Methods

Results

Conclusion