Phylogenetic And Biogeographic Study Of Celastrus L.

Celastrus L.is the type genus of Celastraceae(Celastrales).This genus contains ca.30 species that are disjunctlydistributed in the Asia,Oceania,North America,Central and South America and Madagascar,providing an excellent system for studying the speciation mechanism,origin,dispersal of the species and biogeographic patterns of the world.Although there have been studies on morphology and molecular phylogeny,the results of the molecular phylogenetic relationship are inconsistent with the morphological classification system.The historical biogeographic pattern of Celastrus is unkown.In this study,5 genes,included 2 nuclear genes(ETS,ITS)and 3 chloroplast genes(psb A-trn H,rpl16,trn L-F),were used to constructed phylogenetic trees,providing the most comprehensive molecular phylogenetic relationship to date.The sampling range included all subgenus,systems,and groups,with covering all distributions.The result of molecular phylogeny with the obvious differences of Celastrus and Tripterygium in morphological characteristics of fruits and seeds supported Celastrus is a monophyletic group,it and Tripterygium are the closest sister groups to each other.Celasturs can be divided into two clades,one of the clades with seven subclades.The morphology-based classification systems of flower sex,inflorescences,seed number and shape were not supported by the phylogenetic results.In this study,7 stable and highly recognizable characters were selected for ancestor characters states reconstruction.The results showed that the ancestor state of Celastrus are: colors of articulations coincident,the inflorescences axillary and/or terminal,seeds elliptic.In this study,based on the molecular phylogenetic relationship of Celastrus,reliabled fossils were screened for markers,the divergence time was estimated and geographical distribution of ancestors was reconstructed.The result showed that Celastrus originated in Asia at the end of Oligocene(24.78 Ma,95% HPD: 22.21-26.99Ma).In the early Miocene,it dispersed to Central and South America through long-distance dispersal(18.59 Ma,95% HPD: 12.57-23.69 Ma).In the late Miocene,to the south,it dispersed to Oceania through the Lydekker's Line(10.09 Ma,95% HPD: 5.94-15.03 Ma),and then further dispersed to the Madagascar through the long-distance dispersal(3.86 Ma,95% HPD: 1.17-7.25 Ma);it dispersed to North America through the Bering Land Bridge(8.17 Ma,95% HPD: 4.65-11.70 Ma).Although both originated in Asia at the same period,Celastrus diversified more dramatically than Tripterygium in species diversity and distributional range.The key morphological character in Celastrus,which seed contains a red,fleshy aril,may have greatly enhanced its evolutionary success.