Elucidating the role of genetic drift and natural selection in cork oak differentiation regarding drought tolerance |
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Authors: | J A RAMÍREZ-VALIENTE‡ Z LORENZO†‡ A SOTO†‡ F VALLADARES§¶ L GIL†‡ I ARANDA†‡ |
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Institution: | Instituto Nacional de Investigación Agraria y Tecnología Agroalimentaria, Centro de Investigación Forestal, Carretera Coruña Km 7.5, E-28040 Madrid, Spain;, G.I. Genética y Fisiología Forestal. ETSI Montes Universidad Politécnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain;, Unidad Mixta de Genética y Ecofisiología Forestal INIA-UPM;, Instituto de Recursos Naturales, Centro de Ciencias Medioambientales, CSIC, Serrano 115, E-28006 Madrid, Spain;, Departamento de Biología y Geología. Escuela Superior de Ciencias Experimentales y Tecnológicas, Universidad Rey Juan Carlos, c/Tulipán s/n, E-28933 Móstoles, Spain |
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Abstract: | Drought is the main selection agent in Mediterranean ecosystems and it has been suggested as an important evolutionary force responsible for population diversification in these types of environments. However, population divergence in quantitative traits can be driven by either natural selection, genetic drift or both. To investigate the roles of these forces on among-population divergence in ecophysiological traits related to drought tolerance (carbon isotope discrimination, specific leaf area, leaf size and leaf nitrogen content), we compared molecular and quantitative genetic differentiation in a common garden experiment including thirteen cork oak ( Quercus suber L.) populations across a gradient of rainfall and temperature. Population differentiation for height, specific leaf area, leaf size and nitrogen leaf content measured during a dry year far exceeded the molecular differentiation measured by six nuclear microsatellites. Populations from dry-cool sites showed the lowest nitrogen leaf content and the smallest and thickest leaves contrasting with those from humid-warm sites. These results suggest (i) these traits are subjected to divergence selection and (ii) the genetic differences among populations are partly due to climate adaptation. By contrast, the low among-population divergence found in basal diameter, annual growth and carbon isotopic discrimination (a surrogate for water use efficiency) suggests low or no divergence selection for these traits. Among-population differentiation for neutral markers was not a good predictor for differentiation regarding the quantitative traits studied here, except for leaf size. The correlation observed between the genetic differentiation for leaf size and that for molecular markers was exclusively due to the association between leaf size and the microsatellite Qp ZAG46, which suggests a possible linkage between Qp ZAG46 and genes encoding for leaf size. |
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Keywords: | adaptation carbon isotope discrimination drift F ST leaf size Q ST Quercus suber selection |
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