High genetic diversity in an endemic and vulnerable species: evidence from Astragalus cyclophyllon (Fabaceae) in Iran

The genus Astragalus L. with about 3000 species is the largest genus of flowering plants. It is also the largest genus in the flora of Iran with more than 850 taxa. Astragalus cyclophyllon Beck is an endemic taxon belonging to Astragalus sect. Incani DC. It occurs scattered in the steppe and semi-steppe areas of the western and central parts of Iran. This species is one of the most important forage taxa of Astragalus. According to IUCN criteria it has been classified as a vulnerable taxon in Iran, as it occurs in habitats intensely used by herders for their livestock. Here we evaluate the genetic diversity of the populations of this species in Iran to see whether genetic diversity is high or if reductions have already happened. For this purpose, sampling was done in all geographical areas with A. cyclophyllon populations in Iran. In total, 80 individuals representing 29 populations were studied using 33 quantitative and qualitative morphological characters and 10 inter-simple sequence repeat (ISSR) primers. ISSR revealed 240 bands which all were polymorphic. Neighbor-joining cluster analysis divided the individuals in four groups, Principal Coordinate Analysis and Bayesian population assignment analysis in Structure resulted in three genetic units. Morphological variation showed no correlation with the molecular data. The mean of Gst and Nm indices are 0.516 and 0.468, respectively, which indicate a very high genetic differentiation and low gene flow between the studied populations. According to these results, we conclude that genetic diversity is high in this species and that, therefore, the major threat for A. cyclophyllon is currently not related to inbreeding depression in populations, but might be due to livestock grazing that could change the population demographic structure by reducing regular establishment of new offspring.