Historical Biogeography Study Of Cercis L.(Fabaceae)

Cercis L.belongs to Cercidoideae(Leguminosae),which shows a disjunct distribution across the warm temperate zones of Northern Hemisphere.East Asia is suggested to be the main distribution area and the potential origin and differentiation center of Cercis,the genus is considered as the perfect candidate to 1)study the evolutionary mechanism of intercontinental disjunction in Northern Hemisphere and 2)investigate the role of East Asia in diversification of Cerics in Northern Hemisphere.Representative populations were sampled from East Asia,Central Asia,Europe and North America after collecting distribution data by all kinds of means.Genotyping by Sequencing(GBS)and chloroplast genome data were applied to study the population genetic diversity,spatial distribution pattern of genetic variation,demographic history and lineage differentiation.We aim to elucidate the role of East Asia in diversification of Cerics in Northern Hemisphere and interpret the evolutionary mechanism of intercontinental disjunction and evolutionary history of Cercis in Northern Hemisphere.1.Potential habitat of Cercis species based on ecological niche modellingDistribution data of Cercis nine species and two varieties were collected and screened for predicting potential habitats based on environmental data in Last inter-glacial(LIG),Last Glacial Maximum(LGM),Mid-Holocene(MH)and current periods.Multiple glacial refugium of Cercis in different continents were predicted.Based on analysis of variable contributions,precipitation is significant for the xeric species Cercis griffithii Boiss.,while Cercis glabra Pampan.and Cercis chinensis Bunge.were mainly impacted by vairous variables.It is mostly due to their wide distribution range and high adaptability.2.Phylogenetic reconstruction of CercisPhylogenetic analysis of 241 Cercis samples(8 species)was analyzed for GBS and 29 samples(9 species)for chloroplast genomes.Species in East Asia are shown to be the basic clade.Cercis chuniana Met C.was the most divergent one in Cercis.Cercis glabra and Cercis racemosa Olivar.form a clade which is not monophyletic.This result might indicate the gene introgression and hybridization between the two species.Inconsistence occurs in the phylogenetic analysis as Cercis chingii Chun.in Nanling is within the clade of Cercis siliquastrum L.based on chloroplast genome tree,which might be resulted from chloroplast capture.Meanwhile,species in Central Asia,North America and Europe are also not constant in the phylogenetic analysis,which might be due to the maternal inheritance of chloroplast genome.3.Historical biogeography of CercisHistorical biogeographical analysis of 241 Cercis samples(8 species)was conducted based on GBS and 29 samples(9 species)were used for chloroplast genomes.In combination with ENM analysis,four genetic diversity centers were identified,including Nanling Mountains,Luoxiaoshan Mountains and Eastern Mountain area.Based on the phylogenetic reconstruction,divergence time estimation,ancestral areas inference,as well as historical geological events,glacial climatic osscilation and fossil records,Cercis is supposed to originate from East Asia,from where it dispersed to North America and Central Asia via the Bering land bridge and Europe-Asia mainland.Afterwards,species in North America dispersed to Europe via the Atlantic land bridge.Since the beginning of the middle Miocene,several geographical and climatic events occurred,including the Mid-Miocene Cold Event(14.2-13.6 Ma),the Late Miocene drought event(10 Ma)and the Messinian salinity crisis(6 Ma),which influenced the intercontinental disjunction pattern of Cercis in Northern Hemisphere Temperate.4.Population evolutionary history of Cercis chunianaCercis chuniana populations were sampled and used for GBS in order to study the population evolutionary history.In combination with phylogenetics reconstruction,population genetics analysis,as well as scenarios of geological events and glacial climatic changes,multiple glacial refugia of C.chuniana were identified.which include Eastern Mountains,Wuyi Mountains,Luoxiao Mountains and Nanling Mountains.Ancestral area reconstruction indicated that C.chuniana originated from the populations in Tongling Mountain in Eastern mountain area.Vicariance arose especially between Jinggangshan and Dadongshan populations as Luoxiao Mountains and Nanling Mountains played as important role in the geographical barriers of these populations.Therefore,vicariance is suggested to be a major factor shaping the space pattern of genetic variation in C.chuniana.Meanwhile,the vicariance events occurred during Lushan-Dagu interglaciation(early Miocene)based on the divergence time estimation.