PHYLOGEOGRAPHY AND HISTORY OF GIANT GALAPAGOS TORTOISES

Authors

  • Adalgisa Caccone,

    1. Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06520-8106
    2. Yale Institute of Biospherics Studies, Yale University, New Haven, Connecticut 06520-8106
    3. Yale Institute of Biospherics Studies, Yale University, New Haven, Connecticut 06520-8106 E mail: adalgisa.caccone@yale.edu
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  • Gabriele Gentile,

    1. Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06520-8106
    2. Dipartimento di Biologia, Università di Roma “Tor Vergata,” Rome, Italy
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  • James P. Gibbs,

    1. College of Environmental Science and Forestry, State University of New York, Syracuse, New York 13210
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  • Thomas H. Fritts,

    1. The Charles Darwin Foundation for the Galàpagos Islands, 4512 McMurry Avenue, Fort Collins, Colorado 80525
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  • Howard L. Snell,

    1. Charles Darwin Research Station, Puerto Ayora, Santa Cruz, Galàpagos, Ecuador
    2. Department of Biology and Museum of Southwestern Biology, University of New Mexico, Albuquerque, New Mexico 87131
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  • Jessica Betts,

    1. Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06520-8106
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  • Jeffrey R. Powell

    1. Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06520-8106
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Abstract

Abstract.— We examined the phylogeography and history of giant Galàpagos tortoise populations based on mito-chondrial DNA sequence data from 161 individuals from 21 sampling sites representing the 11 currently recognized extant taxa. Molecular clock and geological considerations indicate a founding of the monophyletic Galàpagos lineage around 2–3 million years ago, which would allow for all the diversification to have occurred on extant islands. Founding events generally occurred from geologically older to younger islands with some islands colonized more than once. Six of the 11 named taxa can be associated with monophyletic maternal lineages. One, Geochelone porteri on Santa Cruz Island, consists of two distinct populations connected by the deepest node in the archipelago-wide phylogeny, whereas tortoises in northwest Santa Cruz are closely related to those on adjacent Pinzón Island. Volcan Wolf, the northernmost volcano of Isabela Island, consists of both a unique set of maternal lineages and recent migrants from other islands, indicating multiple colonizations possibly due to human transport or multiple colonization and partial elimination through competition. These genetic findings are consistent with the mixed morphology of tortoises on this volcano. No clear genetic differentiation between two taxa on the two southernmost volcanoes of Isabela was evident. Extinction of crucial populations by human activities confounds whether domed versus saddleback carapaces of different populations are mono- or polyphyletic. Our findings revealed a complex phylogeography and history for this tortoise radiation within an insular environment and have implications for efforts to conserve these endangered biological treasures.

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