Wind-dispersed seeds blur phylogeographic breaks:The complex evolutionary history of Populus lasiocarpa around the Sichuan Basin

The strength of phylogeographic breaks can vary among species in the same area despite being subject to the same geological and climate history due to differences in biological traits.Several important phylogeographic breaks exist around the Sichuan Basin in Southwest China but few studies have focused on wind-dispersed plants.Here,we investigated the phylogeographic patterns and the evolutionary history of Populus lasiocarpa,a wind-pollinated and wind-dispersed tree species with a circum-Sichuan Basin distribution in southwest China.We sequenced and analyzed three plastid DNA fragments(ptDNA) and eight nuclear microsatellites(nSSRs) of 265 individuals of P.lasiocarpa from 21 populations spanning the entire distribution range.Distribution patterns based on nSSR data revealed that there are three genetic groups in P.lasiocarpa.This is consistent with the three phylogeographic breaks(Sichuan Basin,the Kaiyong Line and the 105°E line),where the Sichuan basin acts as the main barrier to gene flow between western and eastern groups.However,the distribution pattern based on ptDNA haplotypes poorly matched the phylogeographic breaks,and wind-dispersed seeds may be one of the main contributing factors.Species distribution modelling suggested a larger potential distribution in the last glacial maximum with a severe bottleneck during the last interglacial.A DIYABC model also suggested a population contraction and expansion for both western and eastern lineages.These results indicate that biological traits are likely to affect the evolutionary history of plants,and that nuclear molecular markers,which experience higher levels of gene flow,might be better indicators of phylogeographic breaks.

Recent advances on phylogenomics of gymnosperms and a new classification

Living gymnosperms comprise four major groups:cycads,Ginkgo,conifers,and gnetophytes.Relationships among/within these lineages have not been fully resolved.Next generation sequencing has made available a large number of sequences,including both plastomes and single-copy nuclear genes,for reconstruction of solid phylogenetic trees.Recent advances in gymnosperm phylogenomic studies have updated our knowledge of gymnosperm systematics.Here,we review major advances of gymnosperm phylogeny over the past 10 years and propose an updated classification of extant gymnosperms.This new classification includes three classes(Cycadopsida,Ginkgoopsida,and Pinopsida),five subclasses(Cycadidae,Ginkgoidae,Cupressidae,Pinidae,and Gnetidae),eight orders(Cycadales,Ginkgoales,Araucariales,Cupressales,Pinales,Ephedrales,Gnetales,and Welwitschiales),13 families,and 86 genera.We also described six new tribes including Acmopyleae Y.Yang,Austrocedreae Y.Yang,Chamaecyparideae Y.Yang,Microcachrydeae Y.Yang,Papuacedreae Y.Yang,and Prumnopityeae Y.Yang,and made 27 new combinations in the genus Sabina.

Reproduction and genetic diversity of Juniperus squamata along an elevational gradient in the Hengduan Mountains

Elevation plays a crucial factor in the distribution of plants,as environmental conditions become increasingly harsh at higher elevations.Previous studies have mainly focused on the effects of large-scale elevational gradients on plants,with little attention on the impact of smaller-scale gradients.In this study we used 14 microsatellite loci to survey the genetic structure of 332 Juniperus squamata plants along elevation gradient from two sites in the Hengduan Mountains.We found that the genetic structure(single,clonal,mosaic)of J.squamata shrubs is affected by differences in elevational gradients of only 150 m.Shrubs in the mid-elevation plots rarely have a clonal or mosaic structure compared to shrubs in lower-or higher-elevation plots.Human activity can significantly affect genetic structure,as well as reproductive strategy and genetic diversity.Sub-populations at mid-elevations had the highest yield of seed cones,lower levels of asexual reproduction and higher levels of genetic diversity.This may be due to the trade-off between elevational stress and anthropogenic disturbance at mid-elevation since there is greater elevational stress at higher-elevations and greater intensity of anthropogenic disturbance at lower-elevations.Our findings provide new insights into the finer scale genetic structure of alpine shrubs,which may improve the conservation and management of shrublands,a major vegetation type on the Hengduan Mountains and the Qinghai-Tibet Plateau.