Comparative Population Genetics of Astragalus lentiginosus and Its Toxic Fungal Endophyte

Astragalus L. (Leguminosae, Fabaceae) is the most species-rich plant genus in the world, with roughly 3,000 species. These “locoweeds” cause grazing animals to suffer from chronic neurological wasting disease leading to an estimated loss of 100 million dollars annually. These conditions are the result of the toxin swainsonine, which is present in certain species of Astragalus. Swainsonine is not produced by the plant but is a secondary metabolite synthesized by mutualistic fungal endophytes. However, natural swainsonine levels are variable both across and within Astragalus species causing some questions about why some Astragalus varieties exhibit this mutualism and others do not.