Chloroplast phylogeography of Helianthemum songaricum (Cistaceae) from northwestern China: implications for preservation of genetic diversity

Abstract

Two chloroplast intergenic spacers (trnD-trnT and rps16-trnK) were used to study the phylogeographical structure of Helianthemumsongaricum in northwestern China, with 12 haplotypes detected. Phylogenetic analysis showed that H. songaricum comprised two lineages, one distributed in the Yili Valley and the other in the western Ordos Plateau. Nested clade phylogeographic analysis likewise indicated that haplotypes in the Yili Valley and those in the western Ordos Plateau formed sister monophyletic clades. This lineage split was also supported by AMOVA analysis and the Mantel test. AMOVA showed that 99.41% of variance in H. songaricum occurred between the two distribution regions, and correlation between genetic differentiation and geographical distances was significant (r2 = 0.877, P < 0.0001). All populations in the Yili Valley shared haplotype A with high frequency, and range expansion was detected by nested clade analysis and strongly supported by negative Fu’s FS-values, Tajima’s D-values, and mismatch distribution analysis. We speculate that aggravation of the dry and cold climate during the early Quaternary, combined with plant physiological features, were determining factors contributing to the lineage split, and climate oscillations most likely led to the Yili range expansion. The high drift load (FST = 0.9923, GST = 0.663) and inbreeding load (HS = 0.219) of H. songaricum indicate a significant extinction risk, and protective measures should be taken immediately.