Demographic Histories Of Four Spruce(Picea) Species Of The Qinghai

Four closely related spruce species-Picea likiangensis,P. wilsonii,P. purpurea and P. schrenkiana are from Qinghai-Tibetan plateau (QTP) or its neighboring area. Evidents regarding the phylogenetic relationship of the four spruces from phenotypic(P. likiangensis & P. purpurea and P. wilsonii & P. schrenkiana are assigned into two different sects respectively) and Plastid DNA (P. purpurea and P. wilsonii cluster together into one subgroup this time) analyses are not consistent with each other, suggesting that P. purpurea might be the diploid hybrid of P. likiangensis and P. wilsonii. To understand and solve this inconsistence, we may resort to nuclear DNA variation and analyze this variation with several different methods. So far, very few studies have used nuclear DNA variation to study the tree species around QTP. In this study,16 nuclear gene loci were selected to study the demographic history of the four spruce species. The silent nuclear diversity reflected from the 16 nuclear gene loci showed that, except P. schrenkiana that was with restricted variation, all the other three QTP spruces exhibited even higher diversity than some boreal conifers that were more widely distributed. Coalescent-based analysis of the nuclear DNA variation suggested that all the three QTP spruces are compatible with either standard neutral model (P. wilsonii and P. likiangensis) or population growth model (P. purpurea), while the boreal conifers were shown to have suffered from a serious bottleneck by earlier studies. To check the suggested hybrid origin of P. purpurea from P. wilsonii and P. likiangensis, model-based inference of population structure, MIMAR analysis based on isolation-with-migration model (IM model), together with the latest theoretical achievement about how introgression influences diversity distribution, were combined. In the model-based inference of population structure using software Structure, P. likiangensis, P. wilsonii, and P. schrenkiana dominate three different clusters respectively, while P. purpurea scatters among the three clusters, and more prefers the cluster dominated by P. schrenkiana. In agreement with Structure analysis, MIMAR analysis showed that, the divergent time of P. purpurea from P. schrenkiana is shorter than that of P. wilsonii and P. likiangensis from P. schrenkiana. In a word, P. purpurea is not a simple diploid hybrid of P. wilsonii and P. likiangensis, its origin is very probably complicated and may be involved with other spruce species.