The Phylogeographic Structure And Climate Response Characteristics Of Three Spring Blossom Osmanthus Species

Climate change profoundly affects the species distribution pattern.How species respond to the global climate warming is one of the hot issues in current species conservation research.As a global biodiversity hot spot area,Southwest China is an unexceptionable natural experimental field for the climate response characteristics study of plants for its high sensitivity to climate change.China is the origin and evolution center of Osmanthus,and the Southwest Mountain may be one of the most important origin areas.As an important concomitant species of subtropical evergreen broad-leaved forest in China,the phylogeographic structure of the Osmanthus plant and its adaptability to the climate change since the Pleistocene is almost blank.In this paper,three spring blossom osmanthus trees,e.g.Osmanthus serrulatus Rehd.,O.yunnanensis(Franch.)P.S.Green and O.delavayi Franch.,which mainly distributed in the mountain area of Southwest China were chosen as the research objects.The suitable area change of the three species since the Last Glacial Maximum(LGM)were simulated by the Maxent and Bioclim ecological niche modelling.Meanwhile,two chloroplast fragments(trn S-G,mat K)were used to study the phylogeography of 218individuals from 13 populations of the three species.The population genetic structure and haplotype geographic distribution pattern of each population were analyzing,aim to speculate the impact of climate change on species distribution of the Quaternary Glacial Period.Furthermore,the transcriptome sequencing was used to screen and verify the differentially expressed genes(DEGs)adapted to the low temperature environment,and the relationship between genes and the environment was explored through functional enrichment.It hopes to provide a scientific basis for the genetic structure conservation and utilization.The main conclusions of this study are as follows:1)The immense variability in hydrothermal condition determines the geographicl boundary of plants.In the key climatic factors affecting the three Osmanthus,temperature and moisture are the most important factors that determine their distribution.The Maxent model indicates the precipitation warmest quarter is essential to the geographical distribution of the three Osmanthus,of which O.serrulatus and O.yunnanensis have similar response to the climate change.However,bioclim model combined with SPSS analysis indicates that the suitable area of three Osmanthus depends on the effects of temperature and water factors.The O.serrulatus is more sensitive to moisture,and O.delavayi is more sensitive to temperature,while O.yunnanensis is between the former two species with is a strong adaptability to habitat.With the continuous intensification of climate warming,the wild population of three Osmanthus may face a great threat in the future.2)Under the influence of global climate change,the overall suitable area of the three Osmanthus is continuous reducing since LGM,with a trend of transference from low altitude to high altitude and low latitude to high latitude.With the on-going interference of artificial activities,there is a significant fragmentation in the suitable habitat.The suitable area of O.serrulatus shrank obviously,with a large low-altitude habitat lost in Sichuan Basin,retreated from the basin and its surrounding mountains to the high-altitude mountains around the basin.And the suitable area of O.yunnanensis is concentrated in the Yunnan-Guizhou Plateau and the adjacent mountainous area of southern Sichuan with Guizhou.The suitable area of O.delavayi,which mainly distributed in Yunnan-Guizhou Plateau,retreats to the high-altitude mountain areas from Hengduan Mountain to Daliang Mountain and Wumeng Mountain at the junction of Sichuan and Yunnan.3)A total of 9 haplotypes were detected in the 2 chloroplast fragments.The haplotype diversity of O.serrulatus was the lowest with Hd 0.344,while the highest(0.565)of O.yunnanensis,and 0.467 of O.delavayi.Both O.serrulatus and O.yunnanensis have obvious phylogenetic structures(genetic differentiation coefficient:N_ST>G_ST,p?0.05),and the populations with close relationships tend to be concentrated.The differentiation level of populations of O.serrulatus is significant(F_ST=0.812).AMOVA analysis shows that genetic variation mainly occurs between populations(81.23%),and the variation within populations is small.The genetic variation of O.yunnanensis also occurs mostly between populations(67.15%),which may be related to similar geographical environment,complex terrain of the southwest mountainous region.Among the 9 haplotypes,H1-H6 are the haplotypes of O.serrulatus,with H1,H3 and H6 shared by O.serrulatus and O.yunnanensis,indicating that the two are more closely related.The haplotypes of O.delavayi types are H7,H8 and H9.Among the six haplotypes of O.serrulatus,H1 and H6 are unique to Jinkou River and Xiling Snow Mountain.Xiling Snow Mountain is located in the northwest of the distribution area and blocked by mountains,while the Jinkou River population is located in the conservation area with a good habitat.The haplotype H3 is the most widely distributed,accounting for 80%of all populations.It is speculated that it is an ancient haplotype,which is derived from other haplotypes.The haplotype phylogenetic tree indicates that O.serrulatus was closely related to O.yunnanensis,while the differentiation time of O.delavayi was earlier.The mismatch analysis and neutral test shows that neither the O.serrulatus population nor the O.yunnanensis population had a expansion,but the O.delavayi population expanded,and consistent with the Maxent predictions.4)Base on transcriptome sequencing of three Osmanthus,GO enrichment shows that biological processes account for a relatively large proportion,KEGG enriches the functions of different metabolic pathways,and has the most types of metabolism.This study has shown that climate warming lead a obviously suitable area reducing of the three Osmanthus.Only O.delavayi has experienced a brief expansion after LGM.The area suiting for O.serrulatus has decreased most significantly,with the most sensitive to moisture change which negatively correlated.O.yunnanensis is related to hydrothermal factors,and temperature is a key factor affecting the distribution of O.delavayi.The phylogenetic relationship of O.serrulatus and O.yunnanensis is close,and O.delavayi is earlier differentiated than the other two species.