History and evolution of alpine plants endemic to the Qinghai‐Tibetan Plateau: Aconitum gymnandrum (Ranunculaceae)

Abstract

How Quaternary climatic oscillations affected range distributions and intraspecific divergence of alpine plants on the Qinghai-Tibetan Plateau (QTP) remains largely unknown. Here, we report a survey of chloroplast DNA (cpDNA) and nuclear ribosomal internal transcribed spacer (ITS) DNA variation aimed at exploring the phylogeographical history of the QTP alpine endemic Aconitum gymnandrum. We sequenced three cpDNA fragments (rpl20-rps12 intergenic spacer, the trnV intron and psbA-trnH spacer) and also the nuclear (ITS) region in 245 individuals from 23 populations sampled throughout the species' range. Two distinct lineages, with eastern and western geographical distributions respectively, were identified from a phylogenetic analysis of ITS sequence variation. Based on a fast substitution rate, these were estimated to have diverged from each other in the early Pleistocene approximately 1.45 Ma. The analysis of cpDNA variation identified nine chlorotypes that clustered into two major clades that were broadly congruent in geographical distribution with the two ITS lineages. The east-west split of cpDNA divergence was supported by an amova which partitioned approximately half of the total variance between these two groups of populations. Analysis of the spatial distribution of chlorotypes showed that each clade was subdivided into two groups of populations such that a total of four population groups existed in the species. It is suggested that these different groups derive from four independent glacial refugia that existed during the Last Glacial Maximum (LGM), and that three of these refugia were located at high altitude on the QTP platform itself at that time. Coalescent simulation of chlorotype genealogies supported both an early Pleistocene origin of the two main cpDNA clades and also the 'four-refugia' hypothesis during the LGM. Two previous phylogeographical studies of QTP alpine plants indicated that such plants retreated to refugia at the eastern/south-eastern plateau edge during the LGM and/or previous glacial maxima. However, the results for A. gymnandrum suggest that at least some of these cold-tolerant species may have also survived centrally on the QTP platform throughout the Quaternary.

Range shifts of Potentilla fruticosa on the Qinghai-Tibetan Plateau during glacial and interglacial periods revealed by chloroplast DNA sequence variation

“…This conclusion is supported by the unimodal mismatch distribution of the northeastern populations (Figure 4a), suggesting historical population expansion, and by the star-shaped phylogeny of haplotypes derived from haplotype A (Figure 2), the reduced levels of haplotypic and nucleotide diversity (Table 1), and the prevalence of haplotype A in the northeastern populations (Figure 1). The homogeneous genetic pattern in the northeastern populations is consistent with the AMOVA result, which showed relatively low genetic variation among populations (48.7%) in comparison with other alpine plant species on the Plateau (Chen et al, 2008;Yang et al, 2008;Wang et al, 2009). These patterns are consistent with the results of a simulation study in which sudden expansion from a few populations produced reduced allele diversity and areas of genetic homogeneity (Avise, 2000).…”

“…Recent phylogeographic studies have examined the demographic history of alpine plants across the Plateau (Chen et al, 2008;Yang et al, 2008;Wang et al, 2009). Wang et al (2009) suggested that Aconitum gymnandrum has survived on high-altitude parts of the central Plateau throughout the Quaternary.…”

“…Recent phylogeographic studies have examined the demographic history of alpine plants across the Plateau (Chen et al, 2008;Yang et al, 2008;Wang et al, 2009). Wang et al (2009) suggested that Aconitum gymnandrum has survived on high-altitude parts of the central Plateau throughout the Quaternary. In contrast, Metagentiana striata and Pedicularis longiflora probably expanded from refugia on the eastern edge to the central Plateau during the interglacial and postglacial periods (Chen et al, 2008;Yang et al, 2008).…”

Dispersals of Hyoscyameae and Mandragoreae (Solanaceae) from the New World to Eurasia in the early Miocene and their biogeographic diversification within Eurasia

“…The population structure of Aconitum gymnandrum (Ranunculaceae) recovered two genetic diversification centers on the platform, suggesting that this cold-tolerant species may have survived in some ice-free places on the TP platform during the Quaternary glaciations (Wang et al, 2009). The scenario may be applicable to interpret the origin of Przewalskia.…”

Genetic consequences of postglacial colonization by the endemic Yarkand hare (Lepus yarkandensis) of the arid Tarim Basin

“…In contrast, studies on the Asian biota have been rather limited. The complex topography of East Asia probably provided refugia for species during times of Pleistocene glaciation [14], yet only a few plant and bird species restricted to the Qinghai-Tibetan Plateau (QTP) have been evaluated [15][16][17][18][19][20].…”