Genetic diversity and differentiation processes in the ploidy series of Olea europaea L.: a multiscale approach from subspecies to insular populations

Authors

  • C. GARCÍA-VERDUGO,

    1. Departamento de Biología Vegetal I, Universidad Complutense de Madrid, José Antonio Novais 2, 28040 Madrid, Spain,
    2. Real Jardín Botánico de Madrid, CSIC, Plaza Murillo 2, 28014 Madrid, Spain,
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  • M. F. FAY,

    1. Genetics Section, Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, UK,
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  • C. GRANADO-YELA,

    1. Departamento de Biología Vegetal I, Universidad Complutense de Madrid, José Antonio Novais 2, 28040 Madrid, Spain,
    2. Real Jardín Botánico de Madrid, CSIC, Plaza Murillo 2, 28014 Madrid, Spain,
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  • R. RUBIO DE CASAS,

    1. Departamento de Biología Vegetal I, Universidad Complutense de Madrid, José Antonio Novais 2, 28040 Madrid, Spain,
    2. Real Jardín Botánico de Madrid, CSIC, Plaza Murillo 2, 28014 Madrid, Spain,
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  • L. BALAGUER,

    1. Departamento de Biología Vegetal I, Universidad Complutense de Madrid, José Antonio Novais 2, 28040 Madrid, Spain,
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  • G. BESNARD,

    1. Department of Ecology and Evolution, Biophore, University of Lausanne, 1015 Lausanne, Switzerland,
    2. Imperial College, Silwood Park Campus, Buckhurst Road, Ascot, Berkshire SL5 7PY, UK
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  • P. VARGAS

    1. Real Jardín Botánico de Madrid, CSIC, Plaza Murillo 2, 28014 Madrid, Spain,
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Carlos García-Verdugo, Fax: +34913945034; E-mail: cgarciav@bio.ucm.es

Abstract

Geographical isolation and polyploidization are central concepts in plant evolution. The hierarchical organization of archipelagos in this study provides a framework for testing the evolutionary consequences for polyploid taxa and populations occurring in isolation. Using amplified fragment length polymorphism and simple sequence repeat markers, we determined the genetic diversity and differentiation patterns at three levels of geographical isolation in Olea europaea: mainland-archipelagos, islands within an archipelago, and populations within an island. At the subspecies scale, the hexaploid ssp. maroccana (southwest Morocco) exhibited higher genetic diversity than the insular counterparts. In contrast, the tetraploid ssp. cerasiformis (Madeira) displayed values similar to those obtained for the diploid ssp. guanchica (Canary Islands). Geographical isolation was associated with a high genetic differentiation at this scale. In the Canarian archipelago, the stepping-stone model of differentiation suggested in a previous study was partially supported. Within the western lineage, an east-to-west differentiation pattern was confirmed. Conversely, the easternmost populations were more related to the mainland ssp. europaea than to the western guanchica lineage. Genetic diversity across the Canarian archipelago was significantly correlated with the date of the last volcanic activity in the area/island where each population occurs. At the island scale, this pattern was not confirmed in older islands (Tenerife and Madeira), where populations were genetically homogeneous. In contrast, founder effects resulted in low genetic diversity and marked genetic differentiation among populations of the youngest island, La Palma.

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