Maintenance of genetic differentiation across a transition zone in the sea: discordance between nuclear and cytoplasmic markers

Authors

  • C. Lemaire,

    1. Laboratoire Génome, Populations, Interactions, Adaptation, UMR 5171 CNRS-IFREMER-Université Montpellier II, Station Méditerranéenne de l'Environnement Littoral, Sète, France
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  • J.-J. Versini,

    1. Laboratoire Génome, Populations, Interactions, Adaptation, UMR 5171 CNRS-IFREMER-Université Montpellier II, Station Méditerranéenne de l'Environnement Littoral, Sète, France
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  • F. Bonhomme

    1. Laboratoire Génome, Populations, Interactions, Adaptation, UMR 5171 CNRS-IFREMER-Université Montpellier II, Station Méditerranéenne de l'Environnement Littoral, Sète, France
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François Bonhomme, Laboratoire Génome, Populations, Interactions, Adaptation, UMR 5171 CNRS-IFREMER-Université Montpellier II, Station Méditerranéenne de l'Environnement Littoral, 1 Quai de la daurade, 34200 Séte, France.
Tel.: (+33) 4 67 46 33 72; fax: (+33) 4 67 46 33 99;
e-mail: bonhomme@univ-montp2.fr

Abstract

To investigate the origin and maintenance of the genetic discontinuity between Atlantic and Mediterranean populations of the common sea bass (Dicentrarchus labrax) we analysed the genetic variation at a fragment of mitochondrial cytochrome b sequence for 18 population samples. The result were also compared with new or previously published microsatellite data. Seven mitochondrial haplotypes and an average nucleotidic divergence of 0.02 between Atlantic and Mediterranean populations that matches a Pleistocene allopatric isolation were found. The frequency variation at the cytochrome b locus was many times greater between Atlantic and Mediterranean populations (inline image = 0.67) than at microsatellite loci (inline image = 0.02). The examination of the different evolutionary forces at play suggests that a sex-biased hybrid breakdown is a likely explanation for part of the observed discrepancy between mitochondrial and nuclear loci. In addition, an analysis is made of the correlation between microsatellite loci points towards the possible existence of a hybrid zone in samples from the Alboran Sea.

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