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Absence of evidence for isolation by distance in an expanding cane toad (Bufo marinus) population: an individual-based analysis of microsatellite genotypes

Authors

  • Raphael Leblois,

    1. Department of Zoology and Entomology, University of Queensland, Queensland 4072, Australia,
    2. Laboratoire Modélisation et Biologie Evolutive, CBGP-INRA, 34090 Montpellier, France,
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  • François Rousset,

    1. Laboratoire Génétique et Environnement, CNRS-UMR 5554, 34095 Montpellier, France
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  • Dani Tikel,

    1. Department of Zoology and Entomology, University of Queensland, Queensland 4072, Australia,
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  • Craig Moritz,

    1. Department of Zoology and Entomology, University of Queensland, Queensland 4072, Australia,
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  • Arnaud Estoup

    Corresponding author
    1. Department of Zoology and Entomology, University of Queensland, Queensland 4072, Australia,
    2. Laboratoire Modélisation et Biologie Evolutive, CBGP-INRA, 34090 Montpellier, France,
      Arnaud Estoup. Department of Zoology and Entomology, University of Queensland, Queensland 4072, Australia. Fax: 61 7-33 65 16 55; E-mail:aestoup@zoology.uq.edu.au
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Arnaud Estoup. Department of Zoology and Entomology, University of Queensland, Queensland 4072, Australia. Fax: 61 7-33 65 16 55; E-mail:aestoup@zoology.uq.edu.au

Abstract

The cane toad (Bufo marinus) was introduced in 1935 in Australia, where it spread rapidly. We have tested for isolation by distance by analysing at a local geographical scale a continuous population using seven microsatellite markers and an individual-based method. The matrix of pairwise individual differentiation was not significantly correlated with that of geographical distance. Regression analyses gave a low positive slope of 0.00072 (all individuals) or a negative slope of 0.0017 (individuals with a distance higher than the previously estimated mean dispersal distance). The absence of evidence for isolation by distance favours the hypothesis that the substantial differentiation and autocorrelation previously observed at enzyme loci, mainly results from discontinuities in the colonization process with founder effects occurring at the time of the establishment of new populations.

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