Present addresses: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA, ¶Department of Genetics, University of Georgia, Athens, GA 30602, USA.
Molecular phylogeography of common garter snakes (Thamnophis sirtalis) in western North America: implications for regional historical forces
Article first published online: 3 SEP 2002
Volume 11, Issue 9, pages 1739–1751, September 2002
How to Cite
Janzen, F. J., Krenz, J. G., Haselkorn, T. S., Brodie, E. D. and Edmund D. Brodie III (2002), Molecular phylogeography of common garter snakes (Thamnophis sirtalis) in western North America: implications for regional historical forces. Molecular Ecology, 11: 1739–1751. doi: 10.1046/j.1365-294X.2002.01571.x
- Issue published online: 3 SEP 2002
- Article first published online: 3 SEP 2002
- Received 29 January 2002; revision received 16 May 2002; accepted 16 May 2002
- molecular phylogeography;
- Thamnophis sirtalis
Complete ND2 and partial ND4 and cytochrome b mitochondrial DNA (mtDNA) sequences were analysed to evaluate the phylogeographic patterns of common garter snakes (Thamnophis sirtalis) in western North America. This species is widely distributed throughout North America, and exhibits extensive phenotypic variation in the westernmost part of its range. The overall phylogeographic pattern based on mtDNA sequences is concordant with results from studies of other species in this region, implicating historical vicariant processes during the Pleistocene and indicating bottleneck effects of recent dispersal into postglacial habitat. Indeed, the topology is statistically consistent with the hypothesis of both southern (Great Basin and California) and northern (Haida Gwaii) refugia. Specifically, we identified genetic breaks among three major clades: Northwest Coastal populations, Intermountain populations, and all California populations. The California clade contained the only other well-supported branching patterns detected; relationships among populations within the two northern clades were indistinguishable. These molecular splits contrast sharply with all prior geographical analyses of phenotypic variation in T. sirtalis in this region. Our results suggest that the extensive phenotypic variation in western T. sirtalis has been shaped more by local evolutionary forces than by shared common ancestry. Consequently, we consider all morphologically based subspecies designations of T. sirtalis in this region invalid because they do not reflect reciprocal monophyly of the mtDNA sequences.