Abstract
Quaternary climate and environment oscillations have profoundly shaped the population dynamic history and geographic distributions of current plants. However, how the endangered and rare tree species respond to the climatic and environmental fluctuations in the subtropical regions of China in East Asia still needs elucidation. In this study, we collected 36 natural populations of an endangered and rare tree species Magnolia sprengeri Pamp. in subtropical China to determine the demographic history, and modeled the changes of geographic distributions of this species in East Asia based on the MaxEnt ecological niche analyses. In addition, we sequenced three maternally inherited chloroplast DNA fragments (matK, trnH-psbA, and rbcL) for all the natural populations which covered the whole geographic distributions of M. sprengeri. Population genetic analysis showed that the endangered tree species have a low level of chloroplast DNA diversity. However, the genetic variation contribution within populations was greater than that among populations (FST = 0.276), which demonstrated a high level of genetic differentiation. Interestingly, some unique chloroplast DNA haplotypes and higher genetic variations were identified in the Qinling-Daba Mountains, Central China, and Tianmu Mountains of Zhejiang province, East of China in East Asia. Combining with the species distribution modeling, we speculated that these areas might be the potential glacial refugia for the endangered plant M. sprengeri. Phylogeographic analysis demonstrated that the geographic factors (e.g., mountains, rivers, and other isolation barriers) had little effect on the genetic divergence among populations. Ecological niche modeling further revealed that the natural populations of M. sprengeri did not experience significant geographic distribution changes from the last glacial maximum to the present time. These findings are in line with the analysis results of the multimodal mismatch patterns of the chloroplast DNA variations. To protect the endangered species M. sprengeri, in situ and ex situ conservation strategies should be formulated for the natural populations with higher genetic variations.
Highlights
During the Quaternary periods, the global climate experienced repeated cycles of glacial and interglacial stages [1], which lead to the changes of geographic distributions and genetic structures of most organisms [2]
We focused on Magnolia sprengeri Pamp., a long-lived mediumsized deciduous tree belonging to the family Magnoliaceae [24]
The results showed that M. sprengeri was the most widely distributed in LGM, which indicated that the population expansion event occurred in the cold climate period of the Last Glacial Maximum
Summary
During the Quaternary periods, the global climate experienced repeated cycles of glacial and interglacial stages [1], which lead to the changes of geographic distributions and genetic structures of most organisms [2]. It is generally assumed that the isolations between biological refugees lead to the formation of new species or subspecies, especially those with a weak migratory capacity [5]. A recent study suggested that cold-tolerant trees in Europe had to keep a relatively stable population size in the distribution areas during the last glacial period [6]. The studies of the Quaternary glacial age’s influence on the genetic structure and geographical distribution of current biological populations are closely related to the origin, diffusion, and conservation of species diversity [9,10,11,12]. In conjunction with coalescent models of population genetic structure, these studies may improve our understanding of the factors that promote population divergence and form the regional patterns of biodiversity [13]
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