Study On The Species Distribution Pattern Of Chinese Polyploidy Angiosperms

Polyploidization plays a key role in the origin and diversification of angiosperms and is an important driving force of speciation.The Chinese angiosperm flora has a long evolutionary history and high species diversity,with more than 30,000 species.However,it is still remains unknown on the distribution patterns and driving forces of Chinese angiosperm polyploids.Thus,this study investigated this at three scales from the Chinese angiosperm flora to the genus Actinidia and to the Actinidia chinensis mixed-ploidy complex.The study methods and results are as follow.(1)Chinese angiosperm flora: This study inferred the ploidy of Chinese angiosperm species based on the chromosome number of 8,167 species and found that about 33.15% of species are polyploids.The monocot group has the highest polyploid frequency,and the magnoliids group has the highest polyploid speciation frequency.For the spatial distribution patterns of Chinese angiosperm species,the polyploid frequency showed a pattern of west-high and east-low alone the boundary of the Hu Huanyong line.The highest polyploid frequency region lied on the Qinghai-Tibet Plateau.The paleopolyploid frequency showed an opposite trend compared to polyploid frequency.Mean annual temperature and annual precipitation were the main driving forces of the geographic distribution patterns of polyploids and paleopolyploids.In addition,life-form was another important factor in shaping the geographic distribution patterns of polyploids and paleopolyploids.The “polyploid survival index” showed a west-high-east-low geographical trend.These results suggest that polyploidization and rediploidization play key roles in western differentiation centers of herbaceous plants and in the eastern “Cradle” and “Museum” of woody plants,respectively.(2)The Actinidia genus: Phylogenetic and evolutionary history of the Actinidia genus was reconstructed based on cp DNA+ITS sequences.Species within the genus Actinidia diverged in the early Neogene,with most of species(85%)formed within～10 million years.Simulation results of the chromosome evolution model found that the basic chromosome number of the Actinidia genus have underwent palaeopolyploidization followed by aneuploidization.Five polyploidization events have been occurred within the genus,two of which were associated with speciation.Mixed-ploidy species with diploids and polyploids have greater niche differentiation than both polyploid species and diploid species.We found that the higher the ploidy diversity is,the stronger the tolerance of the species to extreme climate.In addition,the stronger the mixed ploidy effect is,the wider the ecological amplitude of temperature and water,which leads to a stronger capacity of tolerance to low temperature and drought.(3)The Actinidia chinensis mixed-ploidy complex: We detected the mixedploidy populations of wild A.chinensis in the Siming mountain,Zhejiang province and the Junzipao mountain,Hubei province,respectively.The Siming mountain population in the east of China mainly include diploids and tetraploids,and the tetraploidy is the dominant ploidy.The Junzipao mountain population in the west of China mainly tetraploids and hexaploids,with the dominant ploidy of hexaploidy.The high ploidy species of the A.chinensis mixed-ploidy complex prefer to live at western regions and high altitude areas.The results are consistent with those from the Chinese angiosperm flora and the genus Actinidia scales,indicating that species with higher ploidy have wider ecological niche and higher tolerance.In summary,this study explored the distribution patterns and driving forces of polyploid species at the Chinese angiosperm flora,the Actinidia genus,and the mixedploidy populations of A.chinensis.Results support the hypothesis that polyploid species have advantage in adaptation to extreme environments,and elucidate the mechanisms of niche differentiation and ecological adaptation in mixed ploidy populations.