Collective tug-of-war dynamics: from molecular motors to ant groups

The emergence of directed transport as a collective behaviour of many microscopic constituents is a ubiquitous problem in the statistical physics of active particles [1]. Examples include flocking and swarming behaviour in fish and birds [2], transport of large cargoes by molecular motors [3] and organisation of ant trails [4]. In all of these examples the active constituents may align their microscopic directions of motions so that a collective transport emerges at the macroscopic scale. A tug-of-war occurs when there are groups of individuals whose microscopic directions are in conflict. This can arise in different kinesin/dynein molecular motors moving along microtubules and connected to a cargo (L1) and in ant trails where there are effectively two directions possible for ants to pull cargoes along a trail (L4). In a tug of war there is a transient period where the two groups cancel each other out, then a transition to one group dominating and directed transport emerging. The objective is to elucidate general mechanisms and conditions which allow emergent directed transport.

We aim to construct and analyse simple particle-based models (T1) for emergent transport. Previously, specific models of molecular attachment [3] and, more recently, coarse-grained description of macroscopic entities [4] have shown that collective motion can emerge from a tug of war when the extrinsic noise in the system is low and the interactions are mean field in nature. The project aims to explore more general models that include nonequilibrium interactions and take into account dimensionality and/or range of interaction between constituents. The DC will identify different universality classes and explore finite size effects, direction reversals, and possible pulsing states. They will also perform analytical calculations (T8) and numerical simulations (T9), and confront the models developed with experimental data.

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[1] Ramaswamy, S. (2010) Annu Rev Condens Matter Phys 1:323 [2] Bialek, W, et al. (2012) Proc Nat Acad Sci 109:471 [3] Müller, MJ, et al. (2008) Proc Nat Acad Sci 105:4609 [4] Pinkoviezky, I, et al. (2018) Phys Rev E 97:032304