Genetic Structure of an Endangered Shrub with a Disjunctive Distribution and the Implications for Conservation

Helianthemum songaricum is a shrub with a disjunctive distribution in Central Asia, the Yili Valley of Xinjiang and the western Ordos Plateau of Inner Mongolia. This plant is at risk of extinction in deteriorating environments. For conservation purposes, we used genotyping by sequencing (GBS) to investigate the full population structure and evolutionary history of this shrub. Based on the GBS data, H. songaricum populations had a low to moderate level of nucleotide diversity, and the populations were classified into six distinct groups by genetic structure analysis. The single nucleotide polymorphism (SNP) data showed strong genetic divergence in the areas of Central Asia, the Yili Valley and the western Ordos Plateau; thus, populations in the western Ordos Plateau should be treated as an independent taxon, integrated based on their other morphology differences from previous studies. We speculate that intense uplift of the crust in the northern Tibetan Plateau and Tianshan Mountains since the late Tertiary caused geographic isolation between the western Ordos Plateau and the Yili Valley, and subsequent Quaternary climate change led to a disruption of gene flow between the regions, leaving those populations distributed deep in valleys of the Tianshan Mountains and western Ordos Plateau at a higher altitude through that period. Within the isolated valleys in the Tianshan Mountains, populations also showed obvious genetic differences from each other. Based on our data, we propose conservation strategies for the species.