S.H. is interested in chipmunk hybridization and bioinformatics. J.S. is a mammalian systematist.
Assessment of gene flow across a hybrid zone in red-tailed chipmunks (Tamias ruficaudus)
Article first published online: 15 JUN 2009
© 2009 Blackwell Publishing Ltd
Volume 18, Issue 14, pages 3097–3109, July 2009
How to Cite
HIRD, S. and SULLIVAN, J. (2009), Assessment of gene flow across a hybrid zone in red-tailed chipmunks (Tamias ruficaudus). Molecular Ecology, 18: 3097–3109. doi: 10.1111/j.1365-294X.2009.04196.x
- Issue published online: 29 JUN 2009
- Article first published online: 15 JUN 2009
- Received 31 July 2008; revision received 14 March 2009; accepted 17 March 2009
- gene flow;
The role of hybridization in animal speciation is controversial and recent research has challenged the long-standing criterion of complete reproductive isolation to attain species status. The speciation-with-gene-flow model posits that the genome is semi-permeable and hybridization may be a phase in the process of divergence. Here, we apply these concepts to a previously identified zone of mtDNA introgression between the two strongly morphologically differentiated subspecies of red-tailed chipmunk (Tamias ruficaudus) in the US Inland Northwest. Using multilocus genotype data from the southern, older contact zone, we demonstrate that neutral gene flow is unusually low between the subspecies across the Lochsa River. This is geographically congruent with the discontinuity in bacular morphology, indicating that the cline of mitochondrial DNA (mtDNA) haplotypes is displaced. Furthermore, we elucidate the evolutionary forces responsible by testing hypotheses of lineage sorting and hybridization. We determined that introgressive hybridization is the cause of mtDNA/morphology incongruence because there are non-zero levels of migration and gene flow. Although our estimate of the age of the hybrid zone has wide credibility intervals, the hybridization events occurred in the Late Pleistocene and the divergence occurred in the Middle Pleistocene. Finally, we assessed substructure within and adjacent to the hybrid zone and found that the hybrid zone constitutes a set of populations that are genetically differentiated from parental sets of populations; therefore, hybridization in this system is not likely an evolutionary sink, but has generated novel combinations of genotypes.