The distribution of three aspen species

Populus davidiana, P. tremula and P. tremuloides are deciduous, obligated outcrossing trees in section Leuce (Populus, Salicaceae) and are keystone taxa in boreal forest communities. These congeners share similar ecological and latitudinal distribution ranges but reside on different continents. Populus davidiana is mainly distributed in mainland China, on the Korean peninsula and in Japan. Populus tremula occurs throughout Europe, Siberia and Xinjiang, China. Populus tremuloides is indigenous to North America and is commonly found above 500 m elevation in the western and northern areas of this continent. To date, the extent and mechanism of evolutionary isolation among these three closely related Populus species have not been specifically investigated. Zhang Jianguo’s research group in RIF, CAF sampled 497 individuals, representing 14 P. davidiana, 13 P. tremula and 6 P. tremuloides populations across the geographic distributions of these species to investigate the nucleotide variation and speciation of these three species with .6 single-copy nuclear loci and 3 chloroplast loci.

These three Populus species harboured relatively high levels of nucleotide diversity and showed high levels of nucleotide differentiation. Phylogenetic analysis revealed that P. tremuloides diverged earlier than the other two species. The cpDNA haplotype network result clearly illustrated the dispersal route from North America to eastern Asia and then into Europe. Molecular dating results confirmed that the divergence of these three species coincided with the sundering of the Bering land bridge in the late Miocene and a rapid uplift of the Qinghai-Tibetan Plateau around the Miocene/Pliocene boundary. Vicariance-driven successful allopatric speciation resulting from historical tectonism and climate oscillations most likely played roles in the formation of the disjunct distributions and divergence of these three Populus species.

This study was published in Molecualr Ecology (IF=6.494) titled “Multilocus Analysis of Nucleotide Variation and Speciation in Three Closely Related Populus (Salicaceae) Species”. Wang Zhaoshan and Du Shuhui from RIF were first co-authors of this paper. Financial support for this research was provided by the National Natural Science Foundation of China and Beijing Co-building Plan for Scientific Research and Postgraduate Education.