An analysis of genetic variation in Astragalus cremnophylax var cremnophylax a critically endangered plant, using AFLP markers

A recently developed molecular technique (amplified fragment length polymorphisms, AFLP) was used for characterizing genetic heterogeneity within and among populations of a critically endangered species of plant, Astragalus cremnophylax var. cremnophylax. Using AFLP, up to 50 polymorphic genetic markers per AFLP-PCR amplification were generated, and a total of 220 variable markers overall. This information was used first to assess genetic diversity within each of the three known populations of Astragalus cremnophylax var. cremnophylax from Grand Canyon National Park in Arizona, USA: North Rim (NR; n = 970), South Rim Site 1 (SR1; n = 500), and South Rim Site 2 (SR2; n = 2). Diversity in the form of average heterozygosity (H) and the proportion of polymorphic genes [P] was greatest in the NR population ([H]= 0.13 and [P] = 0.38) and least in the SR2 population ([H] = 0.02 and [P] = 0.04). Diversity was also quite low for the SR1 population ([H] = 0.04 and [P] = 0.10). In addition, substantial genetic differentiation among populations was indicated by both phenetic (AMOVA) and genetic analyses (overall corrected F-ST = 0.41). This finding was corroborated by the results of several multivariate analyses which utilized the genetic data, including a UPGMA cluster analysis and a principal coordinate analysis which revealed the existence of discrete groups corresponding to the populations. Population structure was further revealed within the NR population which was known to consist of four spatially separated groups of plants. Several recommendations for the future management of the species are discussed.