SummaryWarm-temperate evergreen (WTE) forest represents the typical vegetation type of subtropical China, but how its component species responded to past environmental change remains largely unknown. Here, we reconstruct the evolutionary history of Tetrastigma hemsleyanum, an herbaceous climber restricted to the WTE forest.Twenty populations were genotyped using chloroplast DNA sequences and nuclear microsatellite loci to assess population structure and diversity, supplemented by phylogenetic dating, ancestral area reconstructions and ecological niche modeling (ENM) of the species distributions during the Last Glacial Maximum (LGM) and at present.Lineages in Southwest vs Central-South-East China diverged through climate/tectonicinduced vicariance of an ancestral southern range during the early Pliocene. Long-term stability in the Southwest contrasts with latitudinal range shifts in the Central-South-East region during the early-to-mid-Pleistocene. Genetic and ENM data strongly suggest refugial persistence in situ at the LGM.Pre-Quaternary environmental changes appear to have had a persistent influence on the population genetic structure of this subtropical WTE forest species. Our findings suggest relative demographic stability of this biome in China over the last glacial-interglacial cycle, in contrast with palaeobiome reconstructions showing that this forest biome retreated to areas of today's tropical South China during the LGM.
Context Disturbances may affect the spatial patterns of plant genetic diversity, but these effects are not yet well understood for lack of direct experimental evidence. Grazing is one of such environmental disturbance factors which may lead to small-scale spatial heterogeneity in natural grasslands. Objectives Our main goal was to determine whether a grazing disturbance alters population genetic diversity and genetic structure of the dominant species in the Inner Mongolia Steppe. Methods We performed inter-simple sequence repeat (ISSR) molecular marker analysis on populations of Stipa grandis and S. krylovii which were exposed to five consecutive years of varying degrees of grazing disturbance. Results The amplification results showed that the genetic diversity of both S. grandis and S. krylovii populations varied under different grazing intensities; the highest diversity (Nei's index and Shannon's index) were under moderate disturbance, whereas the lowest under the heavy grazing. The coefficient of gene differentiation (G ST ) of S. grandis and S. krylovii populations were 16.82 and 21.00°%, respectively. These results suggest that the genetic diversity of these two dominant populations was altered by the smallscale grazing disturbance, which provides new evidence supporting the theories of landscape genetics. Conclusions The enhancement of moderate grazing on genetic diversity implies the necessity to involve animal grazing in the design of management regimes for biodiversity conservation of the Inner Mongolia steppes.
Genetic diversity information will be very valuable for future rapeseed {Brassica napus L.) improvement. The genetic diversity and relationships among 92 rapeseed accessions, including 44 from China, 22 from Europe, 16 from the United States, and 10 fronn Canada, were assessed by 60 random amplified polymorphic DNA (RAPD) and 22 expressed sequence tag (EST)-simple sequence repeat (SSR) primers. In total, 618 RAPD and 117 EST-SSR polymorphic fragments were detected. The average number of polymorphic fragments found by each RAPD primer was 10.3 ranging from 3 to 17 and that detected by each pair of EST-SSR primer was 5.3 ranging from 4 to 7. The unweighted pair-group method with arithmetic mean (UPGMA) cluster analysis revealed that these 92 accessions could be classified into three major clusters. Cluster I consisted of accessions mainly from China, which belong to the semi-winter type. Cluster II contained accessions from Europe and the United States, which belong to the winter type. Cluster III was a semi-winter and spring type mixture group, which contained accessions mainly from China and Canada. The principal component analysis and population structure analysis revealed similar results to the cluster analysis. Analysis of molecular variance result based on four geographic groups indicated that genetic variation was 8.24% among populations of geographic regions and 91.76% within geographic regions. Rapeseed accessions from the United Stated have the greatest genetic distance from accessions of other geographic origins, especially those from China. United States rapeseed could be important germplasm resources for enriching the genetic background of Chinese rapeseed and vice versa.
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