Abstract
It has been hypothesized that species occurring in the eastern and the western Qinghai–Tibet Plateau (QTP) responded differently to climate changes during the Pleistocene. Here, we test this hypothesis by phylogeographic analysis of two sister species, Allium cyathophorum and A. spicata. We sequenced two chloroplast DNA (cpDNA) fragments (accD-psaI and the rpl16 intron) of 150 individuals, and the nuclear (ITS) region of 114 individuals, from 19 populations throughout the distributional ranges of these species. The divergence between the two species was dated at 779 - 714 thousand years before the present and was likely initiated by the most major glaciation in the QTP. Analysis of chlorotype diversity showed that A. spicata, the species occurring in the western QTP, contains much lower genetic diversity (0.25) than A. cyathophorum (0.93), which is distributed in the eastern QTP. Moreover, multiple independent tests suggested that the A. spicata population had expanded recently, while no such expansion was detected in A. cyathophorum, indicating a contrasting pattern of responses to Pleistocene climate changes. These findings highlight the importance of geographical topography in determining how species responded to the climate changes that took place in the QTP during the Pleistocene.
Highlights
Responses to climate changes during the Pleistocene have previously been investigated for many plant and animal species in the Qinghai–Tibet Plateau (QTP) and other regions using phylogeographical analyses (Hewitt 2000; Arbogast and Kenagy 2001; Hickerson et al 2010; Sandel et al 2011; Liu et al 2012)
Many of the species distributed in the eastern QTP have been hypothesized to contain higher genetic diversity than species occurring the western QTP (Liu et al 2012, 2014), indicating that geological topography may have played a role in determining the responses of different species to Pleistocene climate changes, such as the responses in genetic diversity and range size (Bellard et al 2012)
Dating analyses using the approximate Bayesian computation (ABC) method suggested that the divergence between A. cyathophorum and A. spicata occurred 779–714 Ka, at the time of the most major glacial period (~600–1200 Ka) in the QTP (Shi et al 1998)
Summary
Responses to climate changes during the Pleistocene have previously been investigated for many plant and animal species in the Qinghai–Tibet Plateau (QTP) and other regions using phylogeographical analyses (Hewitt 2000; Arbogast and Kenagy 2001; Hickerson et al 2010; Sandel et al 2011; Liu et al 2012). Many of the species distributed in the eastern QTP have been hypothesized to contain higher genetic diversity than species occurring the western QTP (Liu et al 2012, 2014), indicating that geological topography may have played a role in determining the responses of different species to Pleistocene climate changes, such as the responses in genetic diversity and range size (Bellard et al 2012). These comparative analyses have always focused on taxa with different life histories and/or biological preference. We report the findings of a study that investigates the responses to these climate changes in a pair of sister species, Allium cyathophorum Bur. & Franch. and A. spicata Prain, which are distributed in the QTP and adjacent regions (Chen et al 2000)
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