MUTUALISM OR PARASITISM? USING A PHYLOGENETIC APPROACH TO CHARACTERIZE THE OXPECKER-UNGULATE RELATIONSHIP

Authors

  • Charles L. Nunn,

    1. Department of Human Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138
    2. E-mail: cnunn@oeb.harvard.edu
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  • Vanessa O. Ezenwa,

    1. Division of Biological Sciences, University of Montana, Missoula, Montana 59812
    2. Odum School of Ecology and Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, Georgia 30602
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  • Christian Arnold,

    1. Department of Human Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138
    2. Bioinformatics Group, Department of Computer Science and Interdisciplinary Center for Bioinformatics, University of Leipzig, Härtelstraße 16-18, D-04107 Leipzig, Germany
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  • Walter D. Koenig

    1. Hastings Reservation and Museum of Vertebrate Zoology, University of California, Berkeley, California 94720-3160
    2. Lab of Ornithology and Department of Neurobiology and Behavior, Cornell University, Ithaca, New York 14850
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Abstract

With their striking predilection for perching on African ungulates and eating their ticks, yellow-billed (Buphagus africanus) and red-billed oxpeckers (B. erythrorhynchus) represent one of the few potentially mutualistic relationships among vertebrates. The nature of the oxpecker–ungulate relationship remains uncertain, however, because oxpeckers are known to consume ungulate tissues, suggesting that the relationship between oxpeckers and ungulates may also be parasitic. To examine this issue further, we obtained data on oxpecker preferences for different ungulate species, the abundance of ticks on these ungulates, and ungulate hide thickness. In support of the mutualism hypothesis, we found that both species of oxpeckers prefer ungulate hosts that harbor a higher abundance of ticks. We found no evidence that hide thickness—a measure of the potential for parasitism by oxpeckers—predicts oxpecker preferences for different ungulate species. Oxpeckers also prefer larger-bodied ungulates, possibly because larger animals have more ticks, provide a more stable platform upon which to forage, or support more oxpeckers feeding simultaneously. However, the preference for ungulates with greater tick abundance was independent of host body mass. These results support the hypothesis that the relationship between oxpeckers and ungulates is primarily mutualistic.

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