Can deleterious mutations surf deterministic population waves? A functional law of large numbers for a spatial model of Muller's ratchet

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Hauptverfasser: Madeira, João Luiz de Oliveira, Ortgiese, Marcel, Penington, Sarah
Format: Preprint
Veröffentlicht: 2026
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author Madeira, João Luiz de Oliveira
Ortgiese, Marcel
Penington, Sarah
author_facet Madeira, João Luiz de Oliveira
Ortgiese, Marcel
Penington, Sarah
contents The spatial Muller's ratchet is a model introduced by Foutel-Rodier and Etheridge to study the impact of cooperation and competition on the fitness of an expanding asexual population. The model is an interacting particle system consisting of particles performing symmetric random walks that reproduce and die with rates that depend on the local number of particles. For each particle, we keep track of the number of deleterious mutations that it carries, and after each birth event, with some positive probability, the offspring particle can acquire an additional mutation that gives it a lower reproduction rate than its parent. We show that under an appropriate scaling, the process converges weakly to the solution of an infinite system of partial differential equations (PDEs), confirming non-rigorous computations of Foutel-Rodier and Etheridge. In the PDE limit, when the reaction term of the system of PDEs is monostable, we establish bounds on the ratio between the density of particles with a given number of mutations and the density of particles without mutations. If the reaction term satisfies a Fisher-KPP condition, we can also rigorously determine the spreading speed of the population into an empty habitat. Finally, by considering the PDE limit of a form of tracer dynamics, we answer the question of whether deleterious mutations can surf population waves in this setting.
format Preprint
id arxiv_https___arxiv_org_abs_2603_06478
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Can deleterious mutations surf deterministic population waves? A functional law of large numbers for a spatial model of Muller's ratchet
Madeira, João Luiz de Oliveira
Ortgiese, Marcel
Penington, Sarah
Probability
Analysis of PDEs
Populations and Evolution
The spatial Muller's ratchet is a model introduced by Foutel-Rodier and Etheridge to study the impact of cooperation and competition on the fitness of an expanding asexual population. The model is an interacting particle system consisting of particles performing symmetric random walks that reproduce and die with rates that depend on the local number of particles. For each particle, we keep track of the number of deleterious mutations that it carries, and after each birth event, with some positive probability, the offspring particle can acquire an additional mutation that gives it a lower reproduction rate than its parent. We show that under an appropriate scaling, the process converges weakly to the solution of an infinite system of partial differential equations (PDEs), confirming non-rigorous computations of Foutel-Rodier and Etheridge. In the PDE limit, when the reaction term of the system of PDEs is monostable, we establish bounds on the ratio between the density of particles with a given number of mutations and the density of particles without mutations. If the reaction term satisfies a Fisher-KPP condition, we can also rigorously determine the spreading speed of the population into an empty habitat. Finally, by considering the PDE limit of a form of tracer dynamics, we answer the question of whether deleterious mutations can surf population waves in this setting.
title Can deleterious mutations surf deterministic population waves? A functional law of large numbers for a spatial model of Muller's ratchet
topic Probability
Analysis of PDEs
Populations and Evolution
url https://arxiv.org/abs/2603.06478