Phylogeographic patterns of the Aconitum nemorum species group (Ranunculaceae) shaped by geological and climatic events in the Tianshan Mountains and their surroundings

Abstract

To investigate the impacts of ancient geologi- cal and climatic events on the evolutionary history of the Aconitum nemorum species group, including A. nemorum s. str., A. karakolicum, and A. soongoricum; a total of 18 natural populations with 146 individuals were sampled, mainly from grassy slopes or the coniferous forest under- story of the Tianshan Mountain Range and its surround- ings. Two cpDNA intergenic spacer regions (trnS-trnG and psbA-trnH) were sequenced and 16 haplotypes were identified. These were clustered into three divergent lin- eages 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 suggest 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. Our molecular dating indicates 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.