, Volume 138, Issue 8, pp 869–883 | Cite as

Introgression at differentially aged hybrid zones in red-tailed chipmunks

  • Sarah Hird
  • Noah Reid
  • John Demboski
  • Jack Sullivan


Hybrid zones allow us to investigate the maintenance and the break down of reproductive isolation; they are a window into the speciation process. Tamias ruficaudus (red-tailed chipmunk) has a roughly ring-like distribution in the Inland Northwest and includes two morphologically well-differentiated subspecies, T. r. ruficaudus (in the eastern portion of its range) and T. r. simulans (in the western portion). These taxa meet at two contact zones: the Lochsa River in Idaho and 200 km to the north, near Whitefish, Montana. The Lochsa Zone is encompassed within the Clearwater River Drainage, which has been proposed as a glacial refugium for many taxa throughout the Pleistocene, whereas the Whitefish Zone was under the Cordilleran ice sheet during the most recent glacial maxima approximately 10,000 years ago. Mitochondrial DNA introgression has been documented at both contact zones, yet the subspecies remain significantly distinct with respect to bacular morphology and no intermediate morphologies have ever been reported. Here, we elucidate differentiation and introgression of the nuclear genome using ten microsatellite loci and compare findings to previously described mitochondrial DNA haplotype distribution and introgression. We found significant substructure in the nuclear data; each subspecies is divided into at least two genetically distinct demes. At the Lochsa contact zone, individuals restricted to the mtDNA zone of introgression form a distinct deme at microsatellite loci whereas in the younger, Whitefish contact zone, there is no hybrid-zone specific group. The genetic distances of the demes within these two subspecies indicate recent northward expansion.


Hybridization Introgression Speciation Tamias 



We thank J. Good and the UI Mammalogy classes (1999–2003) for assistance with field collection. The Field Museum of Natural History, Royal British Columbia Museum, Victoria, Burke Museum of Natural History and Culture and the Connor (Washington State University) provided tissue samples. L. Waits, M. Cantrell, B. Carstens, M. Koopman and T. Pelletier, C. Baers and two anonymous reviewers provided valuable comments on this manuscript. This work was funded by NSF DEB-0717426 (to JS) and DEB-0716200 (to JD). Analyses were run on the bioinformatics core facility supported by the Initiative for Bioinformatics and Evolutionary Studies (IBEST) and funded by NHI (NCRR 1P20RRO16448-01) and NSF (EPS-809935).


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Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  • Sarah Hird
    • 1
  • Noah Reid
    • 1
  • John Demboski
    • 2
  • Jack Sullivan
    • 3
  1. 1.Department of Biological SciencesLouisiana State UniversityBaton RougeUSA
  2. 2.Department of ZoologyDenver Museum of Nature & ScienceDenverUSA
  3. 3.Department of Biological SciencesUniversity of IdahoMoscowUSA

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