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A restricted hybrid zone between native and introduced red fox (Vulpes vulpes) populations suggests reproductive barriers and competitive exclusion

Authors

  • BENJAMIN N. SACKS,

    1. Canid Diversity and Conservation Laboratory, Center for Veterinary Genetics
    2. Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, Davis, CA 95616, USA
    3. Department of Biological Sciences, California State University, Sacramento, CA 95819, USA
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  • MARCELLE MOORE,

    1. Department of Biological Sciences, California State University, Sacramento, CA 95819, USA
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  • MARK J. STATHAM,

    1. Canid Diversity and Conservation Laboratory, Center for Veterinary Genetics
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  • HEIKO U. WITTMER

    1. Department of Wildlife, Fish, and Conservation Biology, University of California, Davis, CA 95616, USA
    2. School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand
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Ben Sacks, Fax: +1 530 752-3556; E-mail: bnsacks@ucdavis.edu

Abstract

Introduced species can threaten native taxa in multiple ways, including competition and hybridization, which can reduce fitness, alter ecological niches or swamp native genomes. Encroachment and hybridization by introduced species also provide opportunities to study the dynamics of invasiveness and hybridization during early stages following contact. We used 33 microsatellites, 51 single nucleotide polymorphisms and a mtDNA marker to characterize the extent and spatial pattern of encroachment and hybridization between a native, endemic subspecies of red fox (Vulpes vulpes patwin) and an introduced red fox population composed of highly admixed, phylogenetically divergent stock, resulting from a century of domestication. Both nuclear and mtDNA markers indicated that hybridization was primarily restricted to a narrow zone where the two populations came into contact. Although a few introgressed genotypes were detected in the interior of the native range, we found no immigrant foxes or F1 or F2 hybrids there, suggesting native foxes excluded introduced individuals. We speculate that the observed interbreeding at the periphery was facilitated by low densities. In total, 98% of mtDNA haplotypes in the native range were native and 96% of the nuclear ancestry was estimated to be native. Although the introduced range had expanded fivefold over the past four decades, native and non-native haplotypes from museum samples collected in and near the native range three decades earlier showed a similar geographic distribution as today, suggesting that the native range and hybrid zone were relatively stable. We hypothesize that the monogamous mating system of red foxes and other wild canids may enhance their resistance to hybridization because of greater fitness consequences associated with mate discrimination.

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