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Polygenic Adaptation in a Population of Finite Size

1
Leibniz Institute for Evolution and Biodiversity Science, Natural History Museum, 10115 Berlin, Germany
2
Department of Life Science Systems, Technical University of Munich, 85354 Freising, Germany
*
Author to whom correspondence should be addressed.
Entropy 2020, 22(8), 907; https://doi.org/10.3390/e22080907
Received: 5 July 2020 / Revised: 31 July 2020 / Accepted: 15 August 2020 / Published: 18 August 2020
(This article belongs to the Special Issue Statistical Physics of Living Systems)
Polygenic adaptation in response to selection on quantitative traits has become an important topic in evolutionary biology. Here we review the recent literature on models of polygenic adaptation. In particular, we focus on a model that includes mutation and both directional and stabilizing selection on a highly polygenic trait in a population of finite size (thus experiencing random genetic drift). Assuming that a sudden environmental shift of the fitness optimum occurs while the population is in a stochastic equilibrium, we analyze the adaptation of the trait to the new optimum. When the shift is not too large relative to the equilibrium genetic variance and this variance is determined by loci with mostly small effects, the approach of the mean phenotype to the optimum can be approximated by a rapid exponential process (whose rate is proportional to the genetic variance). During this rapid phase the underlying changes to allele frequencies, however, may depend strongly on genetic drift. While trait-increasing alleles with intermediate equilibrium frequencies are dominated by selection and contribute positively to changes of the trait mean (i.e., are aligned with the direction of the optimum shift), alleles with low or high equilibrium frequencies show more of a random dynamics, which is expected when drift is dominating. A strong effect of drift is also predicted for population size bottlenecks. Our simulations show that the presence of a bottleneck results in a larger deviation of the population mean of the trait from the fitness optimum, which suggests that more loci experience the influence of drift. View Full-Text
Keywords: rapid adaptation; highly polygenic trait; population genetics; genetic drift rapid adaptation; highly polygenic trait; population genetics; genetic drift
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Stephan, W.; John, S. Polygenic Adaptation in a Population of Finite Size. Entropy 2020, 22, 907.

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