Cytogeography And Molecular Phylogeography Of Allium Przewalskianum Regel (Liliaceae)

Polyploidization plays an important role in generating high diversity of the current plants. Studies of distributional pattern of diploid and derivative autopolyploid have provided an important insight into evolutionary processes of polyploidization within the morphologically taxonomic species.Few researches have been designed to examine the distribution and origin of intraspecific polyploids in the Qinghai-Tibetan Plateau(QTP).Allium przewalskianum occurs widely in the QTP and adjacent regions with altitudes ranging from 2000 m to 4500 m.We collected a total of 844 individuals from 62 populations and determined their cytotypes over the distribution range of this species.Tetraploids tend to occur in the high altitude;however,the positive association between the ploidy and altitude was only marginally significant(P＜0.05). Contact zones between diploids and tetraploids continued from the north toward the south in the eastern QTP.Two cytotypes have no distinct segregation suture and both of them overlapped in the northeast of this region.Three sets of chloroplast DNA(cpDNA)sequences(trnL-trnF,psbA-trnH,accD-psaI)were obtained for 422 plants of 62 populations also over the distribution range of this species.Eleven cpDNA haplotypes(chlorotypes)were identified and nine of them were found in diploids.In tetraploids,five were found with two endemic ones and the chlorotype B is the commonest.The ITS variations for each plant and population were further sequenced.The genetic divergence was detected between the diploid populations and this cryptic divergence is especially obvious between the north and south diploids.From north to south and west,tetraploids tended to have additive sites that distinguished different diploids.Phylogenetic analyses of ITS sequences further suggested that(1)the north and south diploids clustered into different clades;(2)the north tetraploids clustered together with the local diploids;and(3)the west and south tetraploids clustered with the south diploids.These data together suggested a complex polyploidization process had occurred in this species characterized by the following three factors.First,tetraploids have multiple independent origins.This can be illustrated by the multiple chrolotypes found in the tetraploids.Second,a few tetraploids(those occurring in the north)probably originated by a way of"autopolyploidization".Third,the west and south tetraploids originated following hybridization between the two cryptic diploid lineages,similar to "segmental allopolyploids".The wider distribution of tetraploids may mainly be due to their higher colonization ability to the new niches created by the Quaternary climatic oscillations in the QTP.