L\'evy processes with marked jumps II : Application to a population model with mutations at birth

TL;DR

This paper studies the genealogy of a population with mutations at birth, using Lévy processes to model the coalescent point process and its enrichment with mutation history, establishing convergence results to a Poisson point process.

Contribution

It introduces a framework for the marked coalescent point process with mutations, proving its convergence to a Poisson process under large population limits and different mutation regimes.

Findings

Convergence of the marked coalescent point process to a multivariate Poisson process.

Characterization of the intensity measure using excursion theory for Lévy processes.

Description of mutation patterns as regenerative sets along lineages.

Abstract

Consider a population where individuals give birth at constant rate during their lifetimes to i.i.d. copies of themselves. Individuals bear clonally inherited types, but (neutral) mutations may happen at the birth events. The smallest subtree containing the genealogy of all the extant individuals at a fixed time \tau, is called the coalescent point process. We enrich this process with the history of the mutations that appeared over time, and call it the marked coalescent point process. With the help of limit theorems for L\'evy processes with marked jumps established in a previous work (arXiv:1305.6245), we prove the convergence of the marked coalescent point process with large population size and two possible regimes for the mutations - one of them being a classical rare mutation regime, towards a multivariate Poisson point process. This Poisson point process can be described as the coalescent point process of the limiting population at \tau, with mutations arising as inhomogeneous regenerative sets along the lineages. Its intensity measure is further characterized thanks to the excursion theory for spectrally positive L\'evy processes. In the rare mutations asymptotic, mutations arise as the image of a Poisson process by the ladder height process of a L\'evy process with infinite variation, and in the particular case of the critical branching process with exponential lifetimes, the limiting object is the Poisson point process of the depths of excursions of the Brownian motion, with Poissonian mutations on the lineages.