Demographical history and genetic differentiation of an endemic and endangered Ulmus lamellosa (Ulmus)

Abstract Background: Ulmus lamellosa, an endemic and endangered species and one ancient species of Ulmus, has undergone the climate oscillations and geographical changes. Elucidating its demographical and genetic differentiation is very important for understanding the evolutionary history and ecological adaption of forests in Northern China. Results: According to ITS and Aat sequences, eighteen and twenty-three haplotypes were detected respectively. The haplotype distribution was polymorphic in most populations. All levels-phylogeographic clades were geographically structured, namely THM, YM and YSM groups. Within U. lamellose, higher genetic diversity and significant genetic variation were present, YSM and THM had a relatively higher diversity than that of YM. The divergence of U. lamellosa intraspecies haplotypes occurred during Miocene-Pliocene that associated with Tertiary major geological and/or climatic events, which was supported by the gene exchanges among three groups. During the glaciation, YSM and THM regions might be regarded as refugia for U. lamellose. A range expansion was not expected at the evolutionary process, except the THM group based on ITS data. The series Mountains uplift (such as Yanshan Mountains and Taihang Mountains) in North China after Miocene-Pliocene and subsequently Quaternary climatic oscillations further promoted the divergence among populations. Conclusions: Geographical topology and climate change played a critical role on the phylogeographic structure of U. lamellosa, leaded to the current pattern of U. lamellosa. These results would provide important information and clues for the demographical study of the trees in Northern China.