Introgression of phylogeography lineages of Convolvulus gortschakovii (Convolvulaceae) in the northwest China

The paleo-climatic and paleo-geological changes aggravated the aridification of northwest China during the Pleistocene. Thus, nowadays most regions of northwest China belong to the Asian desert flora subkingdom. However, Tianshan Mountains and Altay Mountains show relatively humid climate and belong to the Eurasian forest subkingdom. In order to investigate the effects of these two climate conditions on distribution of desert plants in northwest China, we selected the aridity adapted species Convolvulus gortschakovii (Convolvulaceae) to study its phylogeographical structure. Two plastid regions (rpl14 - rpl36 and trnT - trnY intron) and the nuclear ribosomal internal transcribed spacer (ITS) region were sequenced in individuals from 25 natural populations across the distribution range of this species in northwest China. Results revealed that all populations of C. gortschakovii were divided into three groups: Junggar Basin, Alataw Mountains – central Tianshan Mountains - Tarim Basin and Alxa Desert. Tianshan Mountains were considered to be great geographic barriers to gene flow between the Junggar Basin and Tarim Basin groups. Junggar Basin is thought to be the ancestral distribution range of C. gortschakovii. In addition, at least two dispersal routes were revealed. The eastern dispersal routes were from Junggar Basin to Alxa Desert, and from Junggar Basin to the central Tianshan Mountains. The western dispersal routes were from the Junggar Basin to the Alataw Mountains, from the Alataw Mountains to the central Tianshan Mountains, and from Tarim Basin to central Tianshan Mountains. In addition, a genetic intersection among the three phylogeographic lineages was identified in the Tianshan Mountains and southeastern Gurbantunggut Desert. According to the influence of mountains on the present conformation of genetic structure of C. gortschakovii, it is inferred that Eurasian forest subkingdom plays an important role in the genetic diversity and dispersal of xerophytes of Asian desert flora subkingdom. In addition, estimation of divergence times suggested that genetic structure in C. gortschakovii has been heavily affected by glaciation and climatic shifts during the Pleistocene.