Big sagebrush (Artemisia tridentata) is the most widely distributed shrub in North America.  There are five subspecies, and these often hybridize along environmental gradients.  Two of these subspecies, basin big sagebrush (A. t. tridentata) and mountain big sagebrush (A. t. vaseyana), hybridize along elevational gradients throughout the Great Basin and Rocky Mountains.  These hybrid zones are important laboratories for testing hybrid zone theory.

The two subspecies of big sagebrush differ in morphology and terpene biochemistry.
                         Basin Big Sagebrush

         Mountain Big Sagebrush

Basin big sagebrush grows at lower elevations.  It usually has a single main trunk. Mountain big sagebrush grows at higher elevations.  It generally has no single main trunk.

                             Salt Creek at Basin Site

Mountain Big Sagebrush on Mt. Nebo

We have planted sagebrush from five populations within the hybrid zone at Salt Creek into three gardens spanning the zone (basin, hybrid, mountain).  From this reciprocal transplant experiment at Salt Creek, we have shown that hybrids have highest fitness within the hybrid zone, which supports the bounded hybrid superiority model rather than the dynamic equilibrium or mosaic hybrid zone models.  Additional studies of this hybrid zone include fitness (Graham et al. 1993, Wang et al. 1997), developmental stability (Freeman et al 1995), respiration and water potential (McArthur et al. 1998), soils (Wang et al. 1998), and terpene biochemistry (Byrd et al. 1999).

     Reciprocal Transplant Garden in the Hybrid Zone Site
      Salt Creek During a Storm

References

Freeman, Byrd, D. W., E. D. McArthur, H. Wang, J. H. Graham, and D. C. Freeman.  1999. Narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata: Asteraceae). VIII. Spatial and temporal patterns of terpenes. Biochemical Systematics and Ecology  27: 11-25.

Freeman, D. C., J. H. Graham, D. W. Byrd, E. D. McArthur, and W. D. Turner.  1995. Narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata: Asteraceae). III. Developmental instability.  American Journal of Botany 82: 1144-1152.

Freeman, D.C., W. A. Turner, E. D. McArthur, and J. H. Graham. 1991. The characterization of a narrow hybrid zone between two subspecies of Big Sagebrush (Artemisia tridentata tridentata and A. t. vaseyana).  American Journal of Botany 78: 805-815.

Graham, J. H., D. C. Freeman, and E. D. McArthur. 1995. Narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata: Asteraceae). II. Selection gradients and hybrid fitness.  American Journal of Botany 82: 709-716.

McArthur, E. D., D. C. Freeman, J. H. Graham, H. Wang, S. C. Sanderson, T. A. Monaco, B. N. Smith. 1998. Narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata: Asteraceae). VI. Respiration and water potential. Canadian Journal of Botany 76: 567-574. (pdf)

Wang, H. D., W. Byrd, J. L. Howard, E. D. McArthur, J. H. Graham, and D. C. Freeman. 1998. Narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata: Asteraceae). V. Soil  properties. International Journal of Plant Science 159: 139-147.

Wang, H., E. D. McArthur, J. H. Graham, and D. C. Freeman. 1997. Narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata: Asteraceae). IV. Reciprocal transplant experiments. Evolution 51: 95-102.

Wang, H., E. D. McArthur, and D. C. Freeman. 1999. Narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata Asteraceae) IX.  Elemental uptake and niche separation.  American Journal of Botany 86: 1099-1107.

Last Updated 6 August 2015