Evolutionary history of an alpine shrub Hippophae tibetana (Elaeagnaceae): allopatric divergence and regional expansion

Abstract

Increasing evidence suggests that geological or climatic events in the past promoted allopatric speciation of alpine plants in the Qinghai-Tibetan Plateau and adjacent region. However, few studies have been undertaken to examine whether such allopatric divergences also occurred within a morphologically uniform species. In the present study, we report the evolutionary history of an alpine shrub species, Hippophae tibetana, based on examining chloroplast DNA (cpDNA) and nuclear ribosomal internal transcribed spacer (ITS) DNA variations. We sequenced two cpDNA fragments (trnL-F and trnS-G) and the nuclear ITS region in 183 individuals collected from 21 natural populations. Ten chlorotypes and 17 ITS types were identified. Phylogenetic analyses of both chlorotypes and ITS sequence variations suggested two distinct lineages distributed in the eastern and western region, respectively. On the basis of the fast and low plant substitution rates, these two lineages were estimated to have diverged from each other between 1 and 4 million years ago, during the period of the major glaciations and orogenic processes. In addition, ITS has undergone the accelerated evolution in two populations in the southern Himalaya isolated by the high mountains with a surprising accumulation of the private variations. The east-west split was also supported by an analysis of molecular variance, which partitioned around 91% of the total cpDNA variance between these two groups of populations. A single chlorotype was found for most populations in eastern or western region, suggesting a recent postglacial expansion within each region. Star-phylogeny and mismatch analyses of all chlorotypes within the eastern group of populations suggested an earlier regional expansion before the Last Glacial Maximum (LGM). The local fixture of the different chlorotypes in multiple populations suggested more than one refugia remained for eastern or western region. Coalescent tests rejected the hypothesis that all current populations originated from a single refugium during the LGM. Instead, they supported hypothesis that two lineages diverged before the late Pleistocene. These findings, when taken together, suggested that this species had experienced long allopatric divergence and recent regional range expansions in response to orogenic processes and the climate changes. The evolutionary history of this shrub species highlights importance of geographical isolations to the intraspecific divergence of alpine plants occurring in the world's ruff.

Evolutionary history of Orinus thoroldii (Poaceae), endemic to the western Qinghai-Tibetan Plateau in China

“…Deep divergences within this species seem to have started since the late Pleistocene, which is in accord with conclusions from numerous studies of other species in this region (e.g., Liu et al, 2002;Wang et al, 2009a;Jia et al, 2011). Moreover, we thought that this kind of deep divergence within O. thoroldii may possibly be as a result of adaption to the origin of divergent aridity habitats, whose mechanism is similar to some previous studies of other arid/desert species Wang et al, 2013;Meng et al, 2014).…”

“…For example, some species that were sensitive to these climate changes retreated from eastern refugia during the glacial stage and re-colonized the central plateau platform (e.g., Zhang et al, 2005;Chen et al, 2008;Yang et al, 2008). However, other cold-tolerant species were able to survive in situ during glacial periods in ice-free microrefugia (Wang et al, 2009a;Opgenoorth et al, 2010;Jia et al, 2011). In such situations, independent genetic lineages appeared in different plateau regions due to isolations among developed ice sheets.…”

Biogeography and evolution of seeder and resprouter forms of Erica coccinea (Ericaceae) in the fire-prone Cape fynbos

“…The high frequency of private ribotypes in seeder populations can neither be explained by geographic isolation, since average pairwise geographic distances are actually shorter in seeder than in resprouter populations (Segarra-Moragues and Ojeda 2010), and both seeder and resprouter forms have equal pollination and seed dispersal traits (Malan 2013). A high frequency of private ribotypes has also been suggested as a signature of accelerated ITS evolution (see Jia et al 2011). Interestingly, our results parallel the higher frequency of private microsatellite alleles in E. coccinea seeder populations reported by Segarra-Moragues and Ojeda (2010), which these authors interpreted as the result of faster rates of new alleles arising in seeder populations owing to their comparatively shorter generation times.…”

“…increased rate of molecular change-in different taxa (e.g. SegarraMoragues and Ojeda 2010; Jia et al 2011).…”

Chloroplast phylogeography of Helianthemum songaricum (Cistaceae) from northwestern China: implications for preservation of genetic diversity

“…In addition, many studies have also indicated that within different allopatric regions, patterns of range shift have been distinct; in some regions, range expansion might have occurred. For example, in the eastern Qinghai-Tibetan Plateau (QTP), most populations of Allium przewalskianum contained multiple haplotypes and showed significant genetic divergence from each other, but in the western QTP, this species experienced an earlier range expansion at the end of the last glacial maximum (LGM) (Wu et al 2010); two distinct lineages of Hippophae tibetana were found distributed in eastern and western regions of the QTP, but within each, populations had experienced a recent postglacial expansion (Jia et al 2011). For those species which are in decline, the identified differentiated populations should be taken into consideration for conservation measures.…”