Effects of Periodic Migration on Selection in Subdivided Populations

Mohammad Amin Masoumi; Kamran Kaveh; Mohammad Reza Ejtehadi

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arXiv · 2610.08160

Effects of Periodic Migration on Selection in Subdivided Populations

Mohammad Amin Masoumi·Kamran Kaveh·Mohammad Reza Ejtehadi

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Abstract

Migration and selection jointly shape evolutionary outcomes in spatially structured populations. Migration can vary over time as ecological shifts, such as changes in sea level, alter habitat connectivity. Here, we study the impact of periodic migration on selection within a geographically subdivided population. Using a two-deme Moran model with spatially heterogeneous selection, we analyze a scenario in which a mutant genotype is advantageous in one habitat and disadvantageous in the other. Keeping the time-averaged migration rate fixed, we vary the period, relative phase, and directional asymmetry of migration and examine the resulting steady-state mutant frequency. We find that migration periodicity generally drives the population toward neutrality: relative to constant migration, it decreases the mutant frequency when mutants are advantageous on average and increases it when they are deleterious, without reversing the direction of selection in the parameter regimes examined. This effect is strongest for out-of-phase migration, which models seasonal migration, and is further enhanced by directional asymmetry. The response to the migration period is generally non-monotonic, with an intermediate characteristic period producing the largest deviation from constant-migration behavior under in-phase migration. These results arise from the coupling between migration and local selection in Moran process: temporal modulation of migration changes not only the exchange of individuals between habitats but also the local population composition on which selection acts. Our results show that populations with identical mean migration rates can show different evolutionary outcomes depending on the temporal organization of gene flow.

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Mohammad Amin Masoumi, Kamran Kaveh, Mohammad Reza Ejtehadi. 2026-10-06. Effects of Periodic Migration on Selection in Subdivided Populations. https://arxiv.org/abs/2610.08160

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