Across two phylogeographic breaks: Quaternary evolutionary history of a mountain aspen (Populus rotundifolia) in the Hengduan Mountains

Biogeographical barriers to gene flow are central to plant phylogeography.In East Asia,plant distribution is greatly influenced by two phylogeographic breaks,the Mekong-Salween Divide and Tanaka-Kaiyong Line,however,few studies have investigated how these barriers affect the genetic diversity of species that are distributed across both.Here we used 14 microsatellite loci and four chloroplast DNA fragments to examine genetic diversity and distribution patterns of 49 populations of Populus rotundifolia,a species that spans both the Mekong-Salween Divide and the Tanaka-Kaiyong Line in southwestern China.Demographic and migration hypotheses were tested using coalescent-based approaches.Limited historical gene flow was observed between the western and eastern groups of P.rotundifolia,but substantial flow occurred across both the Mekong-Salween Divide and Tanaka-Kaiyong Line,manifesting in clear admixture and high genetic diversity in the central group.Wind-borne pollen and seeds may have facilitated the dispersal of P.rotundifolia following prevalent northwest winds in the spring.We also found that the Hengduan Mountains,where multiple genetic barriers were detected,acted on the whole as a barrier between the western and eastern groups of P.rotundifolia.Ecological niche modeling suggested that P.rotundifolia has undergone range expansion since the last glacial maximum,and demographic reconstruction indicated an earlier population expansion around 600 Ka.The phylogeographic pattern of P.rotundifolia reflects the interplay of biological traits,wind patterns,barriers,niche differentiation,and Quaternary climate history.This study emphasizes the need for multiple lines of evidence in understanding the Quaternary evolution of plants in topographically complex areas.

Evolutionary history and phylogeography of Scots pine (Pinus sylvestris L.) in Europe based on molecular markers

In this review we summarized recent historical records and molecular studies on evolutionary history and phylogeography of Scots pine with focus on the European highly fragmented distribution area of the species. Fossilized pollen, plant micro- and macrofossil records provided evidences on the large-scale species’ range shifts and demographic changes during the Quaternary. Populations of Scots pine were documented both in the glacial (incl. full glaciation) and interglacial periods. Recolonization of Europe after the glaciation originated from the (Sub) Mediterranean areas like the Balkan Peninsula but also from around the Eastern Alps and the surroundings of the Danube plain. Fennoscandia and northern European Baltic regions were most probably colonized from two main directions, from Western Europe and from the Russian Plain. Modern history of Scots pine was hardly affected by anthropogenic activities that started to strengthen in the Bronze and Iron Age. Along with the fossil records, molecular genetic tools were used to infer the origin and putative history including migration, differentiation and demography of the species. In this paper we compiled the major publications (30) of molecular genetic studies of the past 20?years derived from distinctly inherited organelle genomes (mitochondrial, chloroplast, nuclear) revealed by different marker systems (mtDNA-cox1, -nad1, -nad3, -nad7, ISSR, cpSSR, nSSR, B-SAP, SNP). It is important to consider that different phylogeographic patterns can be drawn by the analysis of different DNA marker types. Accordingly the use of more than one marker simultaneously outlines the most sophisticated phylogeographical pattern on the genetic lineages and can reveal high differentiation of the European distribution. Combined marker systems and markers derived from coding sequences have also been used to detect species’ phylogeographic patterns, but these were rarely applied to Scots pine. Although new molecular techniques can provide higher resolution data for populations, the reviewed results can shape the direction of further studies.