Data from: Divergence-with-gene-flow within the recent chipmunk radiation (Tamias)

Increasing data have supported the importance of divergence with gene flow
(DGF) in the generation of biological diversity. In such cases, lineage
divergence occurs on a shorter timescale than does the completion of
reproductive isolation. Although it is critical to explore the mechanisms
driving divergence and preventing homogenization by hybridization, it is
equally important to document cases of DGF in nature. Here we synthesize
data that have accumulated over the last dozen or so years on DGF in the
chipmunk (Tamias) radiation with new data that quantify very high rates of
mitochondrial DNA (mtDNA) introgression among para- and sympatric species
in the T. quadrivittatus group in the central and southern Rocky
Mountains. These new data (188 cytochrome b sequences) bring the total
number of sequences up to 1871; roughly 16% (298) of the chipmunks we have
sequenced exhibit introgressed mtDNA. This includes ongoing introgression
between subspecies and between both closely related and distantly related
taxa. In addition, we have identified several taxa that are apparently
fixed for ancient introgressions and in which there is no evidence of
ongoing introgression. A recurrent observation is that these
introgressions occur between ecologically and morphologically diverged,
sometimes non-sister taxa that engage in well-documented niche
partitioning. Thus, the chipmunk radiation in western North America
represents an excellent mammalian example of speciation in the face of
recurrent gene flow among lineages and where biogeography, habitat
differentiation and mating systems suggest important roles for both
ecological and sexual selection.