Abstract
Determining the factors promoting speciation is a major task in ecological and evolutionary research and can be aided by phylogeographic analysis. The Qinling–Daba Mountains (QDM) located in central China form an important geographic barrier between southern subtropical and northern temperate regions, and exhibit complex topography, climatic, and ecological diversity. Surprisingly, few phylogeographic analyses and studies of plant speciation in this region have been conducted. To address this issue, we investigated the genetic divergence and evolutionary histories of three closely related tree peony species (Paeonia qiui, P. jishanensis, and P. rockii) endemic to the QDM. Forty populations of the three tree peony species were genotyped using 22 nuclear simple sequence repeat markers (nSSRs) and three chloroplast DNA sequences to assess genetic structure and phylogenetic relationships, supplemented by morphological characterization and ecological niche modeling (ENM). Morphological and molecular genetic analyses showed the three species to be clearly differentiated from each other. In addition, coalescent analyses using DIYABC conducted on nSSR variation indicated that the species diverged from each other in the late Pleistocene, while ecological niche modeling (ENM) suggested they occupied a larger area during the Last Glacial Maximum (LGM) than at present. The combined genetic evidence from nuclear and chloroplast DNA and the results of ENM indicate that each species persisted through the late Pleistocene in multiple refugia in the Qinling, Daba, and Taihang Mountains with divergence favored by restricted gene flow caused by geographic isolation, ecological divergence, and limited pollen and seed dispersal. Our study contributes to a growing understanding of the origin and population structure of tree peonies and provides insights into the high level of plant endemism present in the Qinling–Daba Mountains of Central China.
Highlights
It is widely known that climatic fluctuations during the Pleistocene strongly impacted the distribution and genetic structure of plant and animal species in both Northern and Southern Hemispheres (Hewitt, 2004; Lu, Heckel, Liang, & Zhang, 2013; Song et al, 2009)
In step 2, the same scenario was the best sup‐ ported (PP = 0.6104), indicating that P. qiui split from P. jishanensis at time t1, while P. rockii split from P. jishanensis at time t2 (Figure 2b)
Results from the approximate Bayesian computation (ABC) analysis indicated that the current population sizes of P. jishanensis (NJ) and P. qiui (NQ) decreased to 9.21 × and 3.29 × from a larger ancestral population size of 9.52 × 103 (A2), respectively (Figure S6)
Summary
It is widely known that climatic fluctuations during the Pleistocene strongly impacted the distribution and genetic structure of plant and animal species in both Northern and Southern Hemispheres (Hewitt, 2004; Lu, Heckel, Liang, & Zhang, 2013; Song et al, 2009). During the Quaternary, the Qinling–Daba Mountains were glacial refugia for such iconic fauna as the giant panda (Ailuropoda melanoleuca) and golden takin (Budorcas taxicolor bedfordi; Axelrod, Shehbaz, & Raven, 1998; Ying, 1994), and are thought to have served as refugia for more than 1,620 endemic Chinese plant species (Dong et al, 2011; Ying, 1994) For this reason and because of their geological, climatic, and ecological diversity, the Qinling–Daba Mountains provide an excel‐ lent setting for studying factors underlying divergence and speciation during the Pleistocene. Our research aimed to (a) investigate patterns of interspecific and intraspecific genetic differ‐ entiation among the three species; (b) estimate times of divergence; (c) test modes of origin and infer the demographic history of each species; and (d) consider effective conservation and management strategies separately for each of the three peony species in Central China
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