article published yes Eniko Szep author 485BB5A4-F248-11E8-B48F-1D18A9856A87 Himani Sachdeva author 42377A0A-F248-11E8-B48F-1D18A9856A87 Nicholas H Barton author 4880FE40-F248-11E8-B48F-1D18A9856A870000-0002-8548-5240 NiBa department This paper analyses the conditions for local adaptation in a metapopulation with infinitely many islands under a model of hard selection, where population size depends on local fitness. Each island belongs to one of two distinct ecological niches or habitats. Fitness is influenced by an additive trait which is under habitat‐dependent directional selection. Our analysis is based on the diffusion approximation and accounts for both genetic drift and demographic stochasticity. By neglecting linkage disequilibria, it yields the joint distribution of allele frequencies and population size on each island. We find that under hard selection, the conditions for local adaptation in a rare habitat are more restrictive for more polygenic traits: even moderate migration load per locus at very many loci is sufficient for population sizes to decline. This further reduces the efficacy of selection at individual loci due to increased drift and because smaller populations are more prone to swamping due to migration, causing a positive feedback between increasing maladaptation and declining population sizes. Our analysis also highlights the importance of demographic stochasticity, which exacerbates the decline in numbers of maladapted populations, leading to population collapse in the rare habitat at significantly lower migration than predicted by deterministic arguments. https://research-explorer.ista.ac.at/download/9252/9886/2021_Evolution_Szep.pdf application/pdfno https://creativecommons.org/licenses/by-nc-nd/4.0/ Wiley2021 eng GeneticsEcologyEvolutionBehavior and SystematicsGeneral Agricultural and Biological Sciences 0014-3820 1558-5646 33742441 00063696630000110.1111/evo.14210 7551030-1045 https://research-explorer.ista.ac.at/record/13062 E. Szep, H. Sachdeva, N.H. Barton, Evolution 75 (2021) 1030–1045. Szep, E., Sachdeva, H., &#38; Barton, N. H. (2021). Polygenic local adaptation in metapopulations: A stochastic eco‐evolutionary model. <i>Evolution</i>. Wiley. <a href="https://doi.org/10.1111/evo.14210">https://doi.org/10.1111/evo.14210</a> Szep E, Sachdeva H, Barton NH. Polygenic local adaptation in metapopulations: A stochastic eco‐evolutionary model. <i>Evolution</i>. 2021;75(5):1030-1045. doi:<a href="https://doi.org/10.1111/evo.14210">10.1111/evo.14210</a> Szep, Eniko, et al. “Polygenic Local Adaptation in Metapopulations: A Stochastic Eco‐evolutionary Model.” <i>Evolution</i>, vol. 75, no. 5, Wiley, 2021, pp. 1030–45, doi:<a href="https://doi.org/10.1111/evo.14210">10.1111/evo.14210</a>. Szep, Eniko, Himani Sachdeva, and Nicholas H Barton. “Polygenic Local Adaptation in Metapopulations: A Stochastic Eco‐evolutionary Model.” <i>Evolution</i>. Wiley, 2021. <a href="https://doi.org/10.1111/evo.14210">https://doi.org/10.1111/evo.14210</a>. E. Szep, H. Sachdeva, and N. H. Barton, “Polygenic local adaptation in metapopulations: A stochastic eco‐evolutionary model,” <i>Evolution</i>, vol. 75, no. 5. Wiley, pp. 1030–1045, 2021. Szep E, Sachdeva H, Barton NH. 2021. Polygenic local adaptation in metapopulations: A stochastic eco‐evolutionary model. Evolution. 75(5), 1030–1045. 92522021-03-20T08:22:10Z2025-06-12T06:35:39Z