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Science 18 January 2008:
Vol. 319. no. 5861, pp. 318 - 320
DOI: 10.1126/science.1151182
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Reports

A Localized Negative Genetic Correlation Constrains Microevolution of Coat Color in Wild Sheep

J. Gratten,1 A. J. Wilson,2 A. F. McRae,3 D. Beraldi,2 P. M. Visscher,3 J. M. Pemberton,2 J. Slate1

The evolutionary changes that occur over a small number of generations in natural populations often run counter to what is expected on the basis of the heritability of traits and the selective forces acting upon them. In Soay sheep, dark coat color is associated with large size, which is heritable and positively correlated with fitness, yet the frequency of dark sheep has decreased. This unexpected microevolutionary trend is explained by genetic linkage between the causal mutation underlying the color polymorphism and quantitative trait loci with antagonistic effects on size and fitness. As a consequence, homozygous dark sheep are large, but have reduced fitness relative to phenotypically indistinguishable dark heterozygotes and light sheep. This result demonstrates the importance of understanding the genetic basis of fitness variation when making predictions about the microevolutionary consequences of selection.

1 Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.
2 Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JT, UK.
3 Genetic Epidemiology, Queensland Institute of Medical Research, Brisbane 4029, Australia.

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