| The establishment of reproductive isolation mechanism is the key to the species formation,the speciation process is the establishment and evolution process of reproductive isolation mechanism,the revelation of various isolation mechanism helps to understand the species diversity maintaining mechanism and the role natural selection played in speciation.The uplift of the Qinghai-Tibet plateau produced many relatives species in short evolutionary history,among Ligularia virgaurea and Ligularia sagitta of noxious weed is in sympatry,but transitional individuals which form between them was not found in the before observation,therefore speculated that does not exist the natural hybrid of the two species,and now it is not understood enough that the two presence of reproductive isolation between sympatric species.This article chooses L.virgaurea and L.sagitta which sympatric affinis distributed in eastern of Qinghai-Tibet plateau as the research object,field observations;floral composition analysis and under fluorescence inverted microscope all these detection method is used,through the study of prezygotic isolation mechanism as comparison and observation of two Ligularia flowering phenology,the pollination biology,the pollen vitality,stigma vitality and affinity of pollen and stigma,the influence of environmental conditions to the degree of isolation is analysed,the main form of prezygotic isolation mechanism and its contribution to keep genetic integrity and possibility to prevent interspecific hybridization are confirmed.Main results are as follows:1?Flower features of two Ligularias is extremely similar,florescence of every single flower is basically identical,raceme florescence of L.virgaurea and L.sagitta respectively is 27.5±2.5d?n=10?and 26.3±3.2d?n=10?,capitulum florescence of L.virgaurea and L.sagitta respectively is 8.5±1.5d?n=30?and 7.5±1.5d?n=30?,tubular flower florescence of L.virgaurea and L.sagitta respectively is 7.2±0.8d?n=158?and6.5±1.5d?n=186?,Ligulate flower florescence of L.virgaurea and L.sagitta respectively is 6.3±1.2d?n=92?and 5.8±1.2d?n=104?;pollen viability of two kinds of Ligularia can keep the higher level in 72 hours,vitality of L.stigma are also for about five days;florescence of L.virgaurea began on June 28,nitial florescence is July 4,full-bloom stage began on July 10,end on July 27,florescence of L.sagitta began on July 20,nitial florescence is July 27,full-bloom stage began on August 1,end on August 14,florescence of two Ligularias is different,the end of L.virgaurea florescence and the start of L.sagitta is still about 7 days period overlaped.2?The diversity of the flower-visiting insects of two kinds of Ligularia in florescence,respectively belonged to Hymenoptera,Diptera,Lepidoptera,total of 11families,Apidae,Bombidae,Satyridae,Syrphidae and noctuidae were mayjor pollinator of the two kinds of Ligularia.Of which flower-visiting frequency of Apis cerana and Apis mellifera of Apidae insects are evidently higher than others?P<0.05?,and the average frequency was 3.13±2.13 times·plant-1·h-1;there are not necessary connection of floral traits,aromatic constituent and pollination insects species between L.virgaurea and L.sagitta.3?In the hand pollination experiment,the proportion of pollen adhered stigma,the average number of pollen adhered single stigma,the average number of pollen germinated of single stigma in the interspecific hybridization pollination of two kinds of Ligularia are all less than the intraspecific pollination,there are significant differences?P<0.05?;there are not significant differences about the proportion of stigma which pollen germinated?P>0.05?.growth rate of pollen tube which entered the stigma of the interspecific hybridization pollination is slower than the intraspecific pollination a large number of callose are generated and accumulated along with the growth of pollen tube,finally growing stopped before it arrive in style,and pollen tube arrive into the style has not been found in the observation of the interspecific hybridization pollination.In brief,In this paper the results of the study indicated,the florescence of L.virgaurea and L.sagitta is different but there is still a overlap period of the pollen communication that showed incompletely time isolation existed between two kinds of Ligularia;the generalization of flower-visiting insects and the same pollinators showed behavior isolation mechanism is not established between two kinds of Ligularia;incompletely isolated of the adhesion phase and the pollen tube growth failure affected by the callose after the hybridization Lead to cannot be completed fertilization,gametophytic isolation of two kinds of Ligularia after hybridization and pollination is formed.Prezygotic isolation of L.virgaurea and L.sagitta is completed by a series of isolation mechanism which transmitted into layers and complementary. |
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