Coalescent processes in subdivided populations subject to recurrent mass extinctions

TL;DR

This paper models the genealogical effects of recurrent mass extinctions on subdivided populations, revealing different coalescent processes depending on recolonization mechanisms and highlighting the impact of local versus global extinction events.

Contribution

It introduces a limiting genealogy framework for subdivided populations under mass extinctions, distinguishing between Kingman's coalescent and multiple merger coalescents based on recolonization dynamics.

Findings

Genealogy can be described by Kingman's coalescent or multiple mergers.

Recolonization mechanisms influence the coalescent process.

Mass extinctions alter the structure of genealogical trees.

Abstract

We investigate the infinitely many demes limit of the genealogy of a sample of individuals from a subdivided population subject to sporadic mass extinction events. By exploiting a separation of timescales property of Wright's island model, we show that as the number of demes tends to infinity the limiting form of the genealogy can be described in terms of the alternation of instantaneous 'scattering' phases dominated by local demographic processes, and extended 'collecting' phases dominated by global processes. When extinction and recolonization events are local, this genealogy is given by Kingman's coalescent and the scattering phase influences only the overall rate of the process. In contrast, if the vacant demes left by a mass extinction event can be recolonized by individuals emerging from a small number of demes, then the limiting genealogy is a colaescent with simultaneous multiple mergers. In this case, the details of the within-deme population dynamics influence not only the overall rate of the coalescent process, but also the statistics of the complex mergers that can occur within sample genealogies. This study gives some insight into the genealogical consequences of mass extinction in structured populations.