Asymmetric Mutualism in Two- and Three-Dimensional Range Expansions

TL;DR

This paper investigates how asymmetry and dimensionality influence mutualism in range expansions, revealing that three-dimensional expansions support mutualism over wider conditions and exhibit complex front roughening effects.

Contribution

It introduces a model accounting for asymmetry and interaction strength, showing that 3D expansions favor mutualism more than 2D, with significant effects on front roughness at phase boundaries.

Findings

Mutualism persists over wider parameter ranges in 3D expansions.

Front roughening increases dramatically at mutualistic phase boundaries.

3D expansions allow mutualism for any positive symmetric benefit.

Abstract

Genetic drift at the frontiers of two-dimensional range expansions of microorganisms can frustrate local cooperation between different genetic variants, demixing the population into distinct sectors. In a biological context, mutualistic or antagonistic interactions will typically be asymmetric between variants. By taking into account both the asymmetry and the interaction strength, we show that the much weaker demixing in three dimensions allows for a mutualistic phase over a much wider range of asymmetric cooperative benefits, with mutualism prevailing for any positive, symmetric benefit. We also demonstrate that expansions with undulating fronts roughen dramatically at the boundaries of the mutualistic phase, with severe consequences for the population genetics along the transition lines.