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Estimating seed vs. pollen dispersal from spatial genetic structure in the common ash

Authors

  • M. Heuertz,

    Corresponding author
    1. Centre de Recherche Public-Gabriel Lippmann, CREBS Research Unit, avenue de la Faïencerie 162a, L-1511 Luxembourg, Luxembourg,
    2. Université Libre de Bruxelles, Laboratoire de Génétique et Ecologie Végétales, chaussée de Wavre 1850, B-1160 Bruxelles, Belgium,
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  • X. Vekemans,

    1. Université Libre de Bruxelles, Laboratoire de Génétique et Ecologie Végétales, chaussée de Wavre 1850, B-1160 Bruxelles, Belgium,
    2. Université de Lille 1, Laboratoire de Génétique et Evolution des Populations Végétales, UMR CNRS 8016 — FR CNRS 1818, F-59655 Villeneuve d’Ascq cedex, France,
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  • J.-F. Hausman,

    1. Centre de Recherche Public-Gabriel Lippmann, CREBS Research Unit, avenue de la Faïencerie 162a, L-1511 Luxembourg, Luxembourg,
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  • M. Palada,

    1. ICAS — Statiunea Simeria & Arboretumul Simeria, RO-2625 Simeria, Romania
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  • O. J. Hardy

    1. Université Libre de Bruxelles, Laboratoire de Génétique et Ecologie Végétales, chaussée de Wavre 1850, B-1160 Bruxelles, Belgium,
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and present address: Myriam Heuertz, Uppsala University, Department of Conservation Biology and Genetics, Norbyvägen 18d, SE−752 36 Uppsala, Sweden. Fax: 0046 18 471 64 24; E-mail: myriamheuertz@gmx.net

Abstract

Spatial genetic structure was analysed with five highly polymorphic microsatellite loci in a Romanian population of common ash (Fraxinus excelsior L.), a wind-pollinated and wind-dispersed tree species occurring in mixed deciduous forests over almost all of Europe. Contributions of seed and pollen dispersal to total gene flow were investigated by analysing the pattern of decrease in kinship coefficients among pairs of individuals with geographical distance and comparing it with simulation results. Plots of kinship against the logarithm of distance were decomposed into a slope and a shape component. Simulations showed that the slope is informative about the global level of gene flow, in agreement with theoretical expectations, whereas the shape component was correlated with the relative importance of seed vs. pollen dispersal. Hence, our results indicate that insights into the relative contributions of seed and pollen dispersal to overall gene flow can be gained from details of the pattern of spatial genetic structure at biparentally inherited loci. In common ash, the slope provided an estimate of total gene dispersal in terms of Wright's neighbourhood size of Nb = 519 individuals. No precise estimate of seed vs. pollen flow could be obtained from the shape because of the stochasticity inherent to the data, but the parameter combinations that best fitted the data indicated restricted seed flow, σs £ 14 m, and moderate pollen flow, 70 m £ σp £ 140 m.

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