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Microsatellite and morphological analysis of population structure in the parthenogenetic freshwater snail Melanoides tuberculata: insights into the creation of clonal variability

Authors

  • S. Samadi,

    1. Génétique & Environnement — CC065, Institut des Sciences de l’Evolution, Université Montpellier II, Place Bataillon, 34095 Montpellier cedex 5, France,
    2. Populations, Génétique et Evolution, CNRS, 91198 Gif-sur-Yvette cedex, France,
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    • Correspondence: S. Samadi, Biologie des Invertébrés Marins et Malacologie, Museum National d’Histoire Naturelle, 55 rue Buffon, 75005 Paris, France. Fax: +33-1-40-79-30-89; E-mail: sarah@mnhn.fr

  • J. Mavárez,

    1. Génétique & Environnement — CC065, Institut des Sciences de l’Evolution, Université Montpellier II, Place Bataillon, 34095 Montpellier cedex 5, France,
    2. CEFE — CNRS, 1919 route de Mende, 34293 Montpellier cedex 5, France,
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  • J.-P. Pointier,

    1. Centre de Biologie et Ecologie Tropicale et Méditerranéenne, EPHE, UMR 5555 CNRS, Avenue de Villeneuve, 66860 Perpignan cedex, France
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  • B. Delay,

    1. CEFE — CNRS, 1919 route de Mende, 34293 Montpellier cedex 5, France,
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  • P. Jarne

    1. Génétique & Environnement — CC065, Institut des Sciences de l’Evolution, Université Montpellier II, Place Bataillon, 34095 Montpellier cedex 5, France,
    2. CEFE — CNRS, 1919 route de Mende, 34293 Montpellier cedex 5, France,
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Abstract

The distribution of variability was studied at various geographical scales in the tropical freshwater snail Melanoides tuberculata, in order to analyse the role of factors shaping this distribution, including the mating system and population dynamics. This parthenogenetic polyploid species reproduces mainly asexually, with males occurring at low frequency. About 800 individuals (38 sites) were sampled from Africa and the Middle East, where the species originated, and from recently colonized habitats in South and Central America, and especially the island of Martinique. We first described variation of general aspects and ornamentation of the shells. This analysis confirms the existence of discrete morphs. Second, individuals were studied at three microsatellite loci, showing that each morph is a genetic clone with some minor variation compatible with models of microsatellite evolution. The genetic analysis also showed much more variation within than between clones. However, two populations from Africa exhibited a large amount of variability, and a mixture of sexual and asexual reproduction might explain these genetic patterns. The worldwide distribution of variability is, therefore, compatible with the African origin of the species, and the introduction of a few clones in other parts of the world. These results also suggest that the distribution of variability in Martinique is influenced by flooding events, and that two morphs from Martinique can be interpreted as hybrids between two pre-existing morphs, based on morphological, genetic and geographical arguments.

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