Population Genetics And Intraspecific Divergence Of Picea Likiangensis Complex

It is difficult to determine intraspecific divergence and range expansions of dominant tree species caused by geological and climatic changes because genetic signatures of these processes are often weak at individual loci due to large effective population sizes and long generation times. However, the analysis of genetic changes across multiple loci can help solve this problem. We sequenced13nuclear loci, two mitochondrial DNAs and three chloroplast DNAs in177individuals sampled from22natural populations of Picea likiangensis. This conifer is a dominant tree of forests that occur in eastern and southern areas of the Qinghai-Tibet Plateau (QTP) and comprises several morphologically distinguished varieties. We tested the hypothesis that the evolutionary history of this species was markedly affected by recent QTP uplifts and Quaternary climatic oscillations. Consistent with the taxonomic delimitation of three varieties examined, all individuals clustered into three genetic groups with inter-variety admixture detected in regions of geographical overlap. Divergence between varieties was estimated to have occurred within the Pliocene during a period of recent QTP uplift and ecological niche modeling based on20ecological variables suggested that niche differentiation between the three varieties was high. Furthermore, modeling of population genetic data indicated that two of the varieties (var. rubescens and var. linzhiensis) had expanded their population sizes after the largest Quaternary glaciation in the QTP, while expansion of the third variety (var. likiangensis) began prior to this, probably following the Pliocene QTP uplift. These findings point to the importance of geological and climatic changes during the Pliocene and Pleistocene as causes of intraspecific diversification and range shifts of dominant tree species in the QTP region.