Speciation Mechanism And Biogeographical Pattern Of Hiptage (Malpighiaceae)

"Malpighiaceae route"is a classical model to explain the plant(especially tropical plants)inter-continental disjunctions and long-distance dispersal,which had been verified in some tropical taxa.In particular,it is of great significance to reveal the modern distribution pattern and diversity formation mechanism of tropical plants.Hiptage Gaertner(Malpighiaceae),which is an endemic for tropical Asian,is the most representative and the farthest lineage of the Malpighiaceae route.It is also a key taxa to understand the formation and distribution pattern of Asian tropical plants and the whole Malpighiaceae route.In this paper,to understand the flower traits variation on interspecies and intraspecies and the transform in pollinator groups and pollination behavior,we studied on a specialized pollination system,mirror-image flowers in Hiptage.Then,to study on the molecular phylogeny,differentiation history,diffusion route,formation and maintenance mechanism of Hiptage,we uesed nuclear gene ITS and RAD-seq of 17 and 25 species,respectively.After that,based on the morphological characteristics and molecular data,two new species we were published.We also made a Key to the species of Hiptage in China at same time.The main results are listed below:1.The mirror-image flower of Hiptage and its pollination ecology.Mirror-image flowers is a specialized pollination system in which the styles on one side and fertile stamens on the other side touch each side of the insect abdomen,respectively.Such divergence in herkogamy could be adaptive to pollinator body size,which relates to pollen placement and stigma contact position.The experimental results show that there was a significant correlation between the herkogamy and the abdomen width of pollinators both in interspecies(R~2=0.9461,P=0.007)and intraspecies(R~2=0.8642,P=0.0045).The relationship between flower hekogamy and pollinator abdomen width remained significant in models that included various alternative environmental and allometric predictor variables.The Mantel test suggest that this cooperative relation is the results of independent evolution rather than the gene flow or common ancestor.It’s consistent with the hypothesis of geographic Mosaic of coevolution.Therefore,the variation caused by the mirror-image flowers of Hiptage leaded to pollination isolation,limited gene flow,and promoted specieation.It is probably one of the main reasons for the speciation and maintenance of Hiptage.Certainly,environment and allometric also play an important role in this process.2.Phylogenetic studies based on of nuclear ITS genes.A molecular phylogeny based on 17 species of Hiptage from North and South Thailand,Philippines,South Vietnam,Hengduan mountains,and the border of Yunnan,Guangxi,and Guizhou of the internal transcribed spacer(ITS)region was recovered for the first time for the genus.Our results showed that the Hiptage is a monophyletic group(PP/BS=1/100)and the oldest taxa of this genus is H.stellulifera of Vietnam.The remaining species of Hiptage sampled formed two separate clades,although with weak support(PP/BS=0.64/52).Most species of Hiptage show reflexed petals,with all species bearing erect petals being recovered on a single clade,suggesting a single origin of erect petals in the genus.Our result also demonstrated the polyphyly in H.benghalensis which is the species widespread across the tropical Asia.3.Biogeography of Hiptage based on RAD-seq.A molecular phylogeny based on RAD sequencing of 25 species of Hiptage,which come from every diversity and endemic center(include North and South Thailand,South Vietnam,Hengduan mountains,and the border of Yunnan,Guangxi,and Guizhou)and surrounding areas(such as Malay Peninsular,Borneo,and Philippines).The results show that the taxa of non-reflexed flower were no longer gether into a single branch.The taxa with 2(or more)calyx glands clustered in single branch indicate that these taxa have the same ancestor.H.benghalensis which widespread Asia should be separated to several species.Based on the estimation of molecular data,Hiptage originated in South Indo-China Peninsula in early Miocene(～17.34 Ma).The ancestor of Hiptage was first separated during the rapid extension of Indo-China Peninsula towards the South China Sea by the Indian plate collision.Subsequently,typical Asian monsoon climate was formed(～8Ma)which accelerated specieation rate of Hiptage.There are three main migration routes of Hiptage,first is from Indo-China Peninsula to Southern China along Hengduan mountains;second is spreads from Indo-China Peninsula to Southern China;third is from Indo-China Peninsula to Philippines along Sundaland.While the typical Asian monsoon climate promotes the northward migration of tropical plants,it transports hot and humid air currents along river valleys to Southwest China,providing the necessary conditions for the survival of tropical plants in the Hengduan Mountains and the border of Yunnan,Guizhou and Guizhou regions.Coupled with the highly fragmented karst landforms,the high mountains and deep valleys,which created the current distribution pattern of Hiptage.4.Discovery and report of new species of HiptageDuring field studies on Hiptage pollination in the northeastern Yunnan,China,we came across two new species of Hiptage,one is Hiptage incurvatum K.Tan&M.X.Ren growing on soil slopes or forest margins and river valleys near Mt.Cangshan,Pingpo Town,Dali City(25°35′N,100°02′E),the other one is Hiptage lushuiensis S.P.Dong,K.Tan&M.X.Ren growing in the an open forests of the Nujiang Gorge in Lushui City at the center of Hengduan Mountains(25°51′N,98°51′E).After consulting the latest literature and all type specimen currently recognized for Hiptage,we concluded that it is a hitherto undescribed species to the science and now we report it here.H.incurvatum is characterised by mericarps with arcuate anterior lateral wings,two large glands on the dorsal sepals,and small glands on the remaining sepals.H.lushuiensis is distinctive for its pink petals,2 or more calyx glands,large and red samara with white hairs.The discovery of these two new species provides a new idea for calyx glands evolution in Hiptage.