The Population Genetics of Cheatgrass Range Expansion in Western North America

Bromus tectorum L. (cheatgrass) has become a dominant species on millions of hectares of rangeland in the western United States.  Introduced from Europe and Asia over 130 years ago, most likely as a grain contaminant, it has established itself as a very successful invader across its North American range.  Not only is cheatgrass responsible for widespread ecological damage through the displacement of native shrub and grass species, but its role as a major fuel source for rangeland fires carries a high economic cost as well.  My lab has used genome resources to develop a set of neutral SNP markers that we are using to assess genetic differences between populations across both the invaded and native ranges.  Our results suggest there is a substantial genetic difference between cheatgrass populations located in mid-elevation sagebrush-steppe habitats and those found in warm and salt desert habitats.  We are testing the hypothesis that range expansion of cheatgrass into desert habitats is due to the relatively more recent arrival of pre-adapted haplotypes from populations located in similar habitats within the native Eurasian range.  Observing how various cheatgrass haplotypes sort into different habitats may help further our understanding of secondary invasion and range expansion of invasive species.