Multilocus analysis of nucleotide variation and speciation in three closely related Populus (Salicaceae) species

Abstract

Historical tectonism and climate oscillations can isolate and contract the geographical distributions of many plant species, and they are even known to trigger species divergence and ultimately speciation. Here, we estimated the nucleotide variation and speciation in three closely related Populus species, Populus tremuloides, P. tremula and P. davidiana, distributed in North America and Eurasia. We analysed the sequence variation in six single-copy nuclear loci and three chloroplast (cpDNA) fragments in 497 individuals sampled from 33 populations of these three species across their geographic distributions. 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.

Phylogenetic and Taxonomic Status Analyses of the Abaso Section from Multiple Nuclear Genes and Plastid Fragments Reveal New Insights into the North America Origin of Populus (Salicaceae)

“…The oldest fossil species ( P. wilmattae ), which occurred in northeastern Utah (USA) in the Middle Eocene (Manchester et al, 1986), is most similar to modern P. mexicana . Many poplar leaves and pollen fossils have been reported from the Eocene sediments of NA (Manchester et al, 1986, 2006; Boucher et al, 2003), which predates any fossil records in Asia (Du et al, 2015). The modern Turanga lineage is also likely an ancestral lineage based on heteroblastic characteristic, with willow-like juvenile leaves and tri-valvate capsules strongly differentiating it from other Populus species.…”

“…The exact location of the origin of the genus Populus remains unclear (Du et al, 2015), although large-scale morphological and molecular phylogenetic analyses of the Populus genus have been conducted in previous studies. Currently, there are two main hypotheses about the origin of the genus.…”

Populus х jrtyschensis Chang Y. Yang in the Altai-Sayan mountain country

“…Тополи возникли на территории Северной Америки (Wang et al, 2014;Du et al, 2015;Liu et al, 2017), откуда расселились в Евразию через Северо-атлантический и Берингов сухопутные мосты. После распада этих межкон-тинентальных трасс дальнейшее видообразование в Евразии было аллопат-рическим, вследствие пространственной репродуктивной изоляции.…”

“…Гибридизация, вероятно, сыграла значительную роль в эволюции рода (Wang et al, 2014;Du et al, 2015;Liu et al, 2017). Древность процессов ги-бридизации в роде Populus была подтверждена филогенетическими иссле-дованиями на основе молекулярных маркеров наследуемых по материнской линии хлоропластной и ядерной ДНК.…”

“…При этом виды секции Aigeiros, вероятно, возникли позже в результате древней гибридизации предков Populus и Tacamahaca, что согла-суется с палеоботаническими результатами, поскольку ископаемые остатки видов секции Aigeiros появляются в отложениях позже (Eckenwalder, 1996). Вероятно, на ранних стадиях эволюции генетическая дивергенция между предками разных секций была слабой, что, в частности, подтверждается фактами древних захватов пластид вследствие гибридизации (Wang et al, 2014;Du et al, 2015;Liu et al, 2017). В настоящее время межсекционная ги-бридизация успешно протекает только между видами Aigeiros и Tacamahaca (Vanden Broeck et al, 2005).…”