A Study Of Pattern And Drivng Forces Of Species Diversification Of Dryopteris In The Sino-Himalayan Region

Dryopteris Adanson(Dryopteridaceae,Polypodiales)is one of the most complex genera in ferns,which contains about 400 species and is widely distributed in tropical,subtropical mountainous and temperate regions across the globe.The Asia continent,especially the Sino-Himalayan and Sino-Japanese floristic regions,is the distribution and diversification center of this genus.There are about 125 Dryopteris species in the Sino-Himalayan region,of which about 56% are endemic.The main objective of this study is to reveal the pattern of species diversity of Dryopteris in this region;and the driving force that promotes the diversity of this genus in the Sino-Himalayan region.Based on extensive sampling and collection of habitat information,305 samples(representing 265 Dryopteris taxa and 25 outgroup taxa)were collected to construct a plastid phylogenetic frameworks and 215 samples(representing 121 Dryopteris taxa and 12 outgroup taxa)were collected to construct a RNA-Seq data phylogenetic frameworks of Dryopteris.The spatio-temporal evolutionary history of Dryopteris was revealed by inferring molecular clock,analyzing the diversification rate and reconstructing the ancestral areas.The phylogeny of the plastid genome data and the low copy nuclear sequences of 233 samples(representing 110 Dryopteris taxa),estimated ploidy level and reproductive model were combined to further infer the species diversity pattern of the Sino-Himalayan Dryopteris.In addition,the correlation analyses between the speciation and environmental factors were also carried out.The main results are as follows.Firstly,a phylogenetic framework of Dryopteris was reconstructed based on plastid genome and RNA-Seq data.The results showed that there were four major clades(MC)in Dryopteris(MC I.Fragrantes,MC II.Dryopteris,MC III.Erythrovariae,and MC IV.Nothoperanema).The MC I is sister to all other three lineages,the MC III and the MC IV are sister to each other,and together are sister to the MC II.The study further showed that within the four major clade,twenty-seven clades can be divided,and the phylogenetic relationships among these clades were largely resolved.However,D.subg.Pycnopteris is not monophyly as species of this subgenus are nested in different clades.Based on the current phylogenetic framework,we focused our next study on the Sino-Himalayan Dryopteris clades within the MC II: the Hirtipedes clade,the Lepidopodae clade,the Fibrillosae clade,the Dryopteris clade,and the Goeringianae clade,and further explore their phylogenetic relationships.The results showed that there were many species with distinct morphological differences from different sections clustered within the Dryopteris clade,implying that taxonomic revisions of some sections should be undertaken.Nuclear-cytoplasmic conflict was found in the Dryopteris clade and the Lepidopodae clade,which may be related to ancient hybridization events.We further analyzed the divergence time and the diversification rate,and reconstructed the ancestral distribution of Dryopteris.The results showed that the divergence time and the diversification rate of Dryopteris are related to global geological history and climate change.It is possible that Dryopteris diverged from its sister group Arachnioides in the Laurasia in the late Cretaceous(ca.73 Ma).During the Oligocene,the main clades of Dryopteris differentiated in different regions of the world.The stem and crown groups of all clades of the Sino-Himalayan Dryopteris clades differentiated in the late Miocene(< 13 Ma),and the diversification rate was highly related to temperature fluctuations and intensification of South Asian monsoon.The species sampling density of the Sino-Himalayan Dryopteris clades was further increased(> 95 %)in order to predict the speciation patterns in this region.Eight possible hybridization,polyploidy and/or apomixis speciation patterns in the 114 SinoHimalayan Dryopteris clades taxa were speculated by integrating all phylogenies of the plastid genome,the low copy nuclear gene(AK1 and pgi C)sequences,the structure analysis,ploidy and reproductive model evaluation.There were 40 apomictic diploid taxa of hybrid origin(35%),followed by 28 apomictic polyploidy of hybrid origin(24%),26 sexual diploid taxa(23%),and 20 taxa of other five speciation patterns(18%).Combined with the analysis of environmental factors,we found that various environments in the Sino-Himalaya region provided physical basis for the species differentiation in Dryopteris.Hybridization greatly enriched species divergence,and apomixis and polyploidy played important roles in species diversification of Dryopteris in the Sino-Himalayan region.It seems that hybridization and polyploidy events happened in the Sino-Himalayan Dryopteris clades with no special environmental factors.The combination of sexual and apomictic reproduction provides alternative basis for the reproduction of different taxa,and apomictic taxa are even likely more adaptive to extreme environments.In sum,this study reconstructed a global phylogenetic framework of Dryopteris,and revealed that the species diversification of Dryopteris in the Sino-Himalayan region was driven by the diversified environment provided,by global temperature change and the intensification of South Asia monsoon since the Miocene.Hybridization and polyploidy events with both sexual and apomictic regeneration modes enhanced the differentiation of species of Dryopteris in the Sino-Himalayan region.