Initial diversification, glacial survival, and continuous range expansion of Gentiana straminea (Gentianaceae) in the Qinghai–Tibet Plateau

Abstract

The Qinghai–Tibet Plateau (QTP) has been considered as one of the most sensitive regions to climate change on Earth, and the growth and distribution of alpine species on this plateau have been suggested to depend greatly on their ability to survive within a small range of temperatures. However, the responses of most species in the QTP to the Quaternary climatic oscillation remain largely unknown. We sequenced two cpDNA fragments and nrITS to examine genetic variations in 22 natural populations across the range of distribution in this region to investigate the phylogeographical distributional pattern of Gentiana straminea (Gentianaceae) in the QTP. The high haplotype diversity from populations on the platform suggested the existence of intraspecific diversification. Molecular dating estimated that all haplotypes have differentiated before the Last Glacial Maximum (LGM). Moreover, the haplotype distribution map based on both cpDNA and nrDNA data suggested expansions from QTP to its outer edges. Finally, ecological niche modeling further demonstrated the glacial survival of this species on the platform and continuous expansion to the platform edge. These findings imply that G. straminea should have experienced initial diversification, glacial survival on the platform, and continuous expansion to the QTP edge during the glacial period.