Abstract
The complex tectonic events and climatic oscillations in the Qinghai-Tibetan Plateau (QTP), the largest and highest plateau in the world, are thought to have had great effects on the evolutionary history of the native plants. Of great interest is to investigate plant population genetic divergence in the QTP and its correlation with the geologic and climatic changes. We conducted a range-wide phylogeographical analysis of M. integrifolia based on the chloroplast DNA (cpDNA) trnL-trnF and trnfM-trnS regions, and defined 26 haplotypes that were phylogenetically divided into six clades dated to the late Tertiary. The six clades correspond, respectively, to highly differentiated population groups that do not overlap in geographic distribution, implying that the mountain ranges acting as corridors or barriers greatly affected the evolutionary history of the QTP plants. The older clade of M. integrifolia only occurs in the southwest of the species' range, whereas the distributions of younger clades extend northeastward in the eastern QTP, suggesting that climatic divergence resulting from the uplift of the QTP triggered the initial divergence of M. integrifolia native to the plateau. Also, the nrDNA ITS region was used to clarify the unexpected phylogenetic relationships of cpDNA haplotypes between M. integrifolia and M. betonicifolia. The topological incongruence between the two phylogenies suggests an ancestral hybridization between the two species. Our study indicates that geographic isolation and hybridization are two important mechanisms responsible for the population differentiation and speciation of Meconopsis, a species-rich genus with complex polyploids.
Highlights
The evolutionary history of plant species could be dramatically influenced by habitat fragmentation [1], [2]
It is well known that complex topography could have great effects on the patterns of population genetic variation in space and time [10]
The common scenario is that the genetic variation was structured as a result of the interglacial re-colonization of the Qinghai-Tibetan Plateau (QTP) platform from multiple glacial refugia, as retrieved by the mtDNA and/or chloroplast DNA (cpDNA) analyses of different kinds of plants
Summary
The evolutionary history of plant species could be dramatically influenced by habitat fragmentation [1], [2]. An increasing number of studies indicated that the rapid decline of population size and restricted gene flow could result in genetic differentiation between populations and genetic diversity loss, giving rise to species extinction and biodiversity decrease [1], [2], [4]. Both evolutionary theory and empirical data indicate that global genetic variation could be maintained or even increased by a fragmented population, and allopatric speciation is prone to occur due to genetic isolation of fragmented populations [5], [6]. The analysis of genetic divergence and gene flow between fragmented populations would be greatly helpful in understanding the process of speciation or extinction under the effects of environmental changes
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