Genetic diversity and structure of the endemic and critically endangered Populus caspica in the Hyrcanian forests

Caspian poplar (Populus caspica Bornm.) is an endemic species from Hyrcanian forests and classified as endangered in Iran. However, there is little information about population genetic structure of remnant populations that could support the development of the suitable conservation strategy for this species. This study was designed to understand how anthropogenic and environmental factors have influenced the pattern of genetic diversity of P. caspica. We sampled 359 individuals from 20 populations. However, after removing the clonal ramets, the genetic parameters were calculated for 314 trees using 14 microsatellite markers. Nine populations showed a significant reduction in effective population size and a genetic bottleneck. The inbreeding coefficient (FIS) ranged from 0.02 to 0.11, and the pairwise FST from 0.018 to 0.224, indicating a low to high level of differentiation among populations. The average proportion of migrants was low (0.008), and it was revealed that the Alborz mountains are a major barrier to gene flow between P. caspica populations in the Hyrcanian forests. Resistance analysis showed that elevation is a significant barrier for gene flow across the eastern and western range of the species. STRUCTURE analysis showed the existence of at least two genetic clusters, whereas GENELAND estimated the number of clusters as three. We propose the maintenance of three natural management units to reduce the risk of extinction of this species in the near future.