Natural selection on cork oak: allele frequency reveals divergent selection in cork oak populations along a temperature cline
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A recent study of population divergence at neutral markers and adaptive traits in cork oak has observed an association between genetic distances at locus QpZAG46 and genetic distances for leaf size and growth. In that study it was proposed that certain loci could be linked to genes encoding for adaptive traits in cork oak and, thus, could be used in adaptation studies. In order to investigate this hypothesis, here we (1) looked for associations between molecular markers and a set of adaptive traits in cork oak, and (2) explored the effects of the climate on among-population patterns in adaptive traits and molecular markers. For this purpose, we chose 9-year-old plants originating from thirteen populations spanning a broad range of climatic conditions. Plants established in a common garden site were genotyped at six nuclear microsatellites and phenotypically characterized for six functional traits potentially related to plant performance. Our results supported the proposed linkage between locus QpZAG46 and genes encoding for leaf size and growth. Temperature caused adaptive population divergence in leaf size and growth, which was expressed as differences in the frequencies of the alleles at locus QpZAG46.
KeywordsQuercus suber Natural selection Overdominance Dominance Additive effects Adaptation
This study was funded by the Spanish Ministry of Environment and DGB (Convenio UPM-DGB), the Spanish Ministry of Science and Innovation (PLASTOFOR, AGL-00536/FOR and BOSALIM, CGL2007-66066-C04-02/CGL2007-66066-C04-03 projects and BES-2005-7573 fellowship). We thank Pedro Díaz-Fernández, Laura Castro, Regina Chambel, José María Climent, Pilar Jiménez and the rest of the people who collaborated in the setting up of the cork oak field common gardens under the EU concerted action on cork oak, FAIR I CT 95 0202. We thank to AEMET (Agencia estatal de Meteorología) for providing the climatic data. We thank Matthew Robson who made a thorough review of the English version and contributed with valuable suggestions. We thank Santiago de Blas, José Antonio Mancha and other field assistants for their help during the experiment. We are grateful to Salustiano Iglesias and DGB for the maintenance of the common gardens. Finally, we would like to thank to Santiago González-Martínez for his useful suggestions and comments on the final version of the manuscript.
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