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Effective population size dynamics reveal impacts of historic climatic events and recent anthropogenic pressure in African elephants

Authors

  • J. B. A. OKELLO,

    1. Molecular Biology Laboratory, Institute of Environment & Natural Resources, Makerere University, PO Box 7298, Kampala, Uganda,
    2. McMaster Ancient DNA Centre, Department of Anthropology, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4L9,
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  • G. WITTEMYER,

    1. Molecular Biology Laboratory, Institute of Environment & Natural Resources, Makerere University, PO Box 7298, Kampala, Uganda,
    2. Save the Elephants, PO Box 54667, Nairobi 00200, Kenya,
    3. Department of Fish Wildlife & Conservation Biology, 115 Wager, Colorado State University, Fort Collins, CO 80523-1401, USA,
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  • H. B. RASMUSSEN,

    1. Save the Elephants, PO Box 54667, Nairobi 00200, Kenya,
    2. Animal Behaviour Research Group, Department of Zoology, University of Oxford, South Park Road, Oxford, OX1 3PS, UK,
    3. Department of Biology, University of Copenhagen, Universitetsparken 15, DK–2100, Copenhagen, Denmark
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  • P. ARCTANDER,

    1. Department of Biology, University of Copenhagen, Universitetsparken 15, DK–2100, Copenhagen, Denmark
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  • S. NYAKAANA,

    1. Molecular Biology Laboratory, Institute of Environment & Natural Resources, Makerere University, PO Box 7298, Kampala, Uganda,
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  • I. DOUGLAS-HAMILTON,

    1. Save the Elephants, PO Box 54667, Nairobi 00200, Kenya,
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  • H. R. SIEGISMUND

    1. Department of Biology, University of Copenhagen, Universitetsparken 15, DK–2100, Copenhagen, Denmark
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  • J. B. A. Okello and G. Wittemyer contributed equally to this study.

Fax: +1 905 522 5993; jokello@mcmaster.ca; georgew@nature.berkeley.edu

Abstract

Two hundred years of elephant hunting for ivory, peaking in 1970–1980s, caused local extirpations and massive population declines across Africa. The resulting genetic impacts on surviving populations have not been studied, despite the importance of understanding the evolutionary repercussions of such human-mediated events on this keystone species. Using Bayesian coalescent-based genetic methods to evaluate time-specific changes in effective population size, we analysed genetic variation in 20 highly polymorphic microsatellite loci from 400 elephants inhabiting the greater Samburu-Laikipia region of northern Kenya. This area experienced a decline of between 80% and 90% in the last few decades when ivory harvesting was rampant. The most significant change in effective population size, however, occurred approximately 2500 years ago during a mid–Holocene period of climatic drying in tropical Africa. Contrary to expectations, detailed analyses of four contemporary age-based cohorts showed that the peak poaching epidemic in the 1970s caused detectable temporary genetic impacts, with genetic diversity rebounding as juveniles surviving the poaching era became reproductively mature. This study demonstrates the importance of climatic history in shaping the distribution and genetic history of a keystone species and highlights the utility of coalescent-based demographic approaches in unravelling ancestral demographic events despite a lack of ancient samples. Unique insights into the genetic signature of mid-Holocene climatic change in Africa and effects of recent poaching pressure on elephants are discussed.

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