Polymerase chain reaction–single strand conformation polymorphism analyses of nuclear and chloroplast DNA provide evidence for recombination, multiple introductions and nascent speciation in the Caulerpa taxifolia complex

Authors

  • I. Meusnier,

    1. Laboratoire de Génétique et Evolution des Populations Végétales, UPRESA CNRS 8016, Bât. SN2, Université de Lille I, 59655 Villeneuve d’Ascq cedex, France,
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  • M. Valero,

    Corresponding author
    1. Laboratoire de Génétique et Evolution des Populations Végétales, UPRESA CNRS 8016, Bât. SN2, Université de Lille I, 59655 Villeneuve d’Ascq cedex, France,
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    • §

      Present address: Equipe Evolution et Génétique des Populations Marines, UMR CNRS 7127, Station Biologique de Roscoff, Place Georges Teissier, BP74, 29682 Roscoff cedex, France.

  • C. Destombe,

    1. Laboratoire de Génétique et Evolution des Populations Végétales, UPRESA CNRS 8016, Bât. SN2, Université de Lille I, 59655 Villeneuve d’Ascq cedex, France,
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    • §

      Present address: Equipe Evolution et Génétique des Populations Marines, UMR CNRS 7127, Station Biologique de Roscoff, Place Georges Teissier, BP74, 29682 Roscoff cedex, France.

  • C. Godé,

    1. Laboratoire de Génétique et Evolution des Populations Végétales, UPRESA CNRS 8016, Bât. SN2, Université de Lille I, 59655 Villeneuve d’Ascq cedex, France,
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  • E. Desmarais,

    1. Laboratoire Génome, Populations, Interactions, CNRS UMR 5000, Université de Montpellier II, SMEL, 1 quai de la daurade, 34200 Sète, France,
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  • F. Bonhomme,

    1. Laboratoire Génome, Populations, Interactions, CNRS UMR 5000, Université de Montpellier II, SMEL, 1 quai de la daurade, 34200 Sète, France,
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  • W. T. Stam,

    1. Department of Marine Biology, Centre for Ecological and Evolutionary Studies, Biological Centre, University of Groningen, PO Box 14, 9750 AA Haren, the Netherlands
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  • J. L. Olsen

    1. Department of Marine Biology, Centre for Ecological and Evolutionary Studies, Biological Centre, University of Groningen, PO Box 14, 9750 AA Haren, the Netherlands
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M. Valero, Equipe Evolution et Génétique des Populations Marines, UMR CNRS 7127, Station Biologique de Roscoff, Place Georges Teissier, BP74, 29682 Roscoff cedex, France. Fax: + 33 2 98 29 23 24; E-mail: valero@sb-roscoff.fr

Abstract

Independent lines of evidence support an Australian origin for the Mediterranean populations of the tropical alga Caulerpa taxifolia. To complement previous biogeographical studies based on nuclear rDNA internal transcribed spacer (ITS), a new chloroplast marker was developed — the cp 16S rDNA intron-2. Sequence variability for both nuclear and chloroplast markers were assessed in 110 individuals using single strand conformation polymorphism. Comparison of intrapopulation genetic diversity between invasive Mediterranean and ‘native’ Australian populations revealed the occurrence of two divergent and widespread clades. The first clade grouped nontropical invasive populations with inshore-mainland populations from Australia, while the second clustered all offshore-island populations studied so far. Despite our finding of nine distinct nuclear and five distinct chloroplast profiles, a single nucleocytoplasmic combination was characteristic of the invasive populations and sexual reproduction was found to be very rare. C. taxifolia is clearly a complex of genetically and ecologically differentiated sibling species or subspecies.

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