Microsatellite analysis of genetic divergence among populations of giant Galápagos tortoises

Authors

  • Claudio Ciofi,

    Corresponding author
    1. Department of Ecology and Evolutionary Biology, and
    2. Yale Institute for Biospheric Studies, Yale University, New Haven, CT 06520–8106, USA,
      Claudio Ciofi. Fax: + 1203 4326066; E-mail: claudio.ciofi@yale.edu
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  • Michel C. Milinkovitch,

    1. Unit of Evolutionary Genetics, Institute of Molecular Biology and Medicine, Free University of Brussels, Rue Jeener and Brachet 12, B-6041 Gosselies, Belgium,
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  • James P. Gibbs,

    1. College of Environmental Science and Forestry, State University of New York, Syracuse, NY 13210, USA
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  • Adalgisa Caccone,

    1. Department of Ecology and Evolutionary Biology, and
    2. Yale Institute for Biospheric Studies, Yale University, New Haven, CT 06520–8106, USA,
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  • Jeffrey R. Powell

    1. Department of Ecology and Evolutionary Biology, and
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Claudio Ciofi. Fax: + 1203 4326066; E-mail: claudio.ciofi@yale.edu

Abstract

Giant Galápagos tortoises represent an interesting model for the study of patterns of genetic divergence and adaptive differentiation related to island colonization events. Recent mitochondrial DNA work elucidated the evolutionary history of the species and helped to clarify aspects of nomenclature. We used 10 microsatellite loci to assess levels of genetic divergence among and within island populations. In particular, we described the genetic structure of tortoises on the island of Isabela, where discrimination of different taxa is still subject of debate. Individual island populations were all genetically distinct. The island of Santa Cruz harboured two distinct populations. On Isabela, populations of Volcan Wolf, Darwin and Alcedo were significantly different from each other. On the other hand, Volcan Wolf showed allelic similarity with the island of Santiago. On Southern Isabela, lower genetic divergence was found between Northeast Sierra Negra and Volcan Alcedo, while patterns of gene flow were recorded among tortoises of Cerro Azul and Southeast Sierra Negra. These tortoises have endured heavy exploitation during the last three centuries and recently attracted much concern due to the current number of stochastic and deterministic threats to extant populations. Our study complements previous investigation based on mtDNA diversity and provides further information that may help devising tortoise management plans.

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