Effects of habitat fragmentation, population size and demographic history on genetic diversity: the cross river gorilla in a comparative context

Authors

  • Richard A. Bergl,

    Corresponding author
    1. Anthropology Department, City University of New York Graduate Center, New York, New York
    2. New York Consortium in Evolutionary Primatology, New York, New York
    • North Carolina Zoological Park, 4401 Zoo Parkway, Asheboro, NC 27205
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  • Brenda J. Bradley,

    1. Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
    Current affiliation:
    1. Department of Zoology and Christ's College, University of Cambridge, Cambridge CB2 3EJ, UK
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  • Anthony Nsubuga,

    1. Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
    Current affiliation:
    1. Genetics Division, Conservation and Research for Endangered Species, 15600 San Pasqual Valley Road, Escondido, CA 92027
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  • Linda Vigilant

    1. Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
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Abstract

In small and fragmented populations, genetic diversity may be reduced owing to increased levels of drift and inbreeding. This reduced diversity is often associated with decreased fitness and a higher threat of extinction. However, it is difficult to determine when a population has low diversity except in a comparative context. We assessed genetic variability in the critically endangered Cross River gorilla (Gorilla gorilla diehli), a small and fragmented population, using 11 autosomal microsatellite loci. We show that levels of diversity in the Cross River population are not evenly distributed across the three genetically identified subpopulations, and that one centrally located subpopulation has higher levels of variability than the others. All measures of genetic variability in the Cross River population were comparable to those of the similarly small mountain gorilla (G. beringei beringei) populations (Bwindi and Virunga). However, for some measures both the Cross River and mountain gorilla populations show lower levels of diversity than a sample from a large, continuous western gorilla population (Mondika, G. gorilla gorilla). Finally, we tested for the genetic signature of a bottleneck in each of the four populations. Only Cross River showed strong evidence of a reduction in population size, suggesting that the reduction in size of this population was more recent or abrupt than in the two mountain gorilla populations. These results emphasize the need for maintaining connectivity in fragmented populations and highlight the importance of allowing small populations to expand. Am. J. Primatol. 70:848–859, 2008. © 2008 Wiley-Liss, Inc.

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