Fixation properties of subdivided populations with balancing selection

TL;DR

This paper studies how balancing selection influences fixation in subdivided populations, revealing phase transitions and complex fixation times, using a new approximation method and an effective voter model for stronger selection.

Contribution

It introduces a novel approximation method based on time scale separation and an effective voter model to analyze fixation under balancing selection in subdivided populations.

Findings

Predicts phase transition between coexistence and loss of biodiversity.

Shows nonmonotonic fixation time dependence on migration rate.

Provides accurate results for small effective selection and large number of subpopulations.

Abstract

In subdivided populations, migration acts together with selection and genetic drift and determines their evolution. Building up on a recently proposed method, which hinges on the emergence of a time scale separation between local and global dynamics, we study the fixation properties of subdivided populations in the presence of balancing selection. The approximation implied by the method is accurate when the effective selection strength is small and the number of subpopulations is large. In particular, it predicts a phase transition between species coexistence and biodiversity loss in the infinite-size limit and, in finite populations, a nonmonotonic dependence of the mean fixation time on the migration rate. In order to investigate the fixation properties of the subdivided population for stronger selection, we introduce an effective coarser description of the dynamics in terms of a voter model with intermediate states, which highlights the basic mechanisms driving the evolutionary process.