Phylogeographic Patterns of the Aconitum nemorum species group (Ranunculaceae) Shaped by Geological and Climatic Events in the Tianshan Mountains and Their Surroundings

Phylogeography, a new discipline which began at 1980s, plays an important role in connecting population genetics and phylogenetic systematics. Since the recent rapid development of this discipline, it has been recognized as an appropriate method to detect the present spatial genetic structures of species and infer the antecedent historical events.

Tianshan Mountains, located between the Tarim and Dzungarian basins in Northwestern China, were mainly formed as a result of the intensive Cenozoic India–Asia collision. Although the chronological process of this uplift is still in debate, it is believed that the most recent uplift of the Tianshan Mountains occurred in the late Tertiary. Also, according to evidence from analysis of palynology and ancient alpine glaciers, climatic cycles of cold-dry to warm-humid conditions were experienced during the late Quaternary in the Tianshan Mountains. These geological events and climatic changes are believed to have profoundly affected the genetic structure and distribution patterns of species.

Considering the timescale of the uplift of the Tianshan Mountains, JIANG Xiaolong et al. studied the phylogeography of the Aconitum nemorum species group, containing A. nemorum s. str., A. soongoricum, and A. karakolicum to provide new perspectives on the evolutionary history of this species group in relation to events in this area.

To investigate the impacts of ancient geological and climatic events on the evolutionary history of the A. nemorum species group, a total of 18 natural populations with 146 individuals were sampled, mainly from grassy slopes or the coniferous forest understory of the Tianshan Mountains and its surroundings. Two cpDNA intergenic spacer regions (trnS-trnG and psbA-trnH) were sequenced and 16 haplotypes were identified. These were clustered into three divergent lineages which almost entirely corresponded to the three species.

Analysis of molecular variance indicated restricted gene flow, mainly among species. High levels of genetic distance were detected among eastern populations in A. nemorum s. str. and A. karakolicum from spatial genetic landscape analysis. Neutral tests and mismatch distribution analysis suggested that A. nemorum s. str. experienced demographic expansions during interglacial periods. Based on haplotype distribution and the median-joining network, it was inferred that this species underwent two periods of eastward expansion. The molecular dating indicated that the lineages of the complex separated during the period of the late Tertiary to late Pleistocene (11.74–0.064 million years ago), which was most likely triggered by recent rapid uplift of the Tianshan Mountains, while genetic variation at the intra-specific level might be attributed to climatic cycles in the late Quaternary.

The result was published in Plant Systematics and Evolution in June 2013.