Abstract
East–west phylogeographic break is common among plant species in subtropical China. However, the estimation time of east–west phylogeographic break has always relied on inferences of calibrated phylogenies, and the contribution of environmental heterogeneity to population differentiation has largely been ignored. In this study, we estimated the divergence time of Asteropyrum populations through coalescent-based approaches based on DNA sequences of ten nuclear loci and evaluated the contribution of environmental heterogeneity to population differentiation. The results showed that there were two chloroplast clades and nuclear groups within Asteropyrum, displaying a subtle pattern of east–west differentiation. The divergence time of the two nuclear groups was dated to ~1.2 Ma, which is associated with climate changes during the Mid-Pleistocene transition. A genetic admixture event between the two genetic groups happened at ~0.46 Ma, resulting in several admixed populations. Isolation by environmental distance (IBE) explained the majority (46.32%) of population differentiation, but that isolation by geographic distance (IBD) only contributed 4.66%. The results of this study suggest that climate changes during the Pleistocene may be a major cause for the east–west phylogeographic break in subtropical China. However, the complex terrain and high environmental heterogeneity in the west of subtropical China (and adjacent regions such as the Hengduan Mountains and the Himalayan Moutains) caused by strong geological uplift may have profoundly shaped the population structure of plant species in subtropical China.
Highlights
In a milestone paper concerning plant molecular phylogeography in China about one decade ago, the authors encouraged Chinese phylogeographers to explicitly state the time scale to which they refer when interpreting their results with respect to refugial isolation or range expansions [1]
Afterwards, a large number of plant phylogeographic studies have been implemented in China following Qiu’s et al (2011) recommendation, which has substantially enhanced our understandings of the evolution and biogeographic history of the world’s most diverse temperate flora since the late Cenozoic [2,3,4,5,6,7,8]
Genetic differentiation was one owing to monomorphism in each population, which was not shown in this study
Summary
In a milestone paper concerning plant molecular phylogeography in China about one decade ago, the authors encouraged Chinese phylogeographers to explicitly state the time scale to which they refer when interpreting their results with respect to refugial isolation or range expansions [1]. DNA sequences of four chloroplast spacer regions, Sun et al (2014) found that the time to the most recent common ancestor of all haplotypes in Tetracentron sinense (Trochodendraceae) was 9.6 million years ago (Ma) [9]. The time estimates in most studies have been based on calibrated phylogenies [2,4,5,6,7,9,10,11], which may reflect the divergence history of genes ( chloroplast genes) rather than divergence history of populations [12] and may compromise the conclusions that have been made. Several coalescent-based approaches such as Approximate Bayesian Computation (ABC) [13] and Isolation with Migration (IM) [14]
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