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1 November 2009 Predicting Adaptation Under Migration Load: The Role of Genetic Skew
Sam Yeaman, Frédéric Guillaume
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Quantitative genetics models have been used to predict the constraints on local adaptation caused by gene flow between populations under migration—selection balance. One key assumption of this approach is that genetic values within a population are normally distributed. Gene flow, however, may generate distributions that are skewed toward the immigrant's mean value. If the response to selection from a skewed distribution is different from that expected under the assumption of normality, models may result in inaccurate predictions. We use individual-based computer simulations to explore this problem, comparing our results to a recent model developed by Hendry et al. (2001). We show that this model underestimates the equilibrium divergence between populations at migration—selection balance. The extent of this underestimation is correlated with the amount of genetic skew generated by migration and is partly explained by the fact that the analytical model ignores direct selection against hybrid phenotypes. We also show that all else being equal, response to selection in a population with a skewed distribution of genotypes is greater than in a population with normally distributed genotypes. The production of skew under migration—selection balance, however, is itself dependent upon the genetic architecture, with greater deviations from normality produced when alleles contributing to population differentiation have very different effect sizes. We find that both the skew and discrepancies between the models are greatest at intermediate migration rates and moderate to strong selection, which is exactly the region of parameter space that is most empirically relevant.

©2009 The Society for the Study of Evolution.
Sam Yeaman and Frédéric Guillaume "Predicting Adaptation Under Migration Load: The Role of Genetic Skew," Evolution 63(11), 2926-2938, (1 November 2009).
Received: 28 January 2009; Accepted: 1 June 2009; Published: 1 November 2009

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Continuum-of-allele model
diallelic model
divergent selection
Gaussian approximation
genetic architecture
quantitative trait
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