Self-pollen Interference And Sexual System Evolution In Akebia Species

Angiosperms are amazing for their complex sexual systems and floral structures.And the direction of plant sexual systems and floral features evolution has always been the focus of botanists.There are multiple pathways from monoecious to dioecious,and various hypotheses have been proposed to predict the evolutionary advantages of dioecious species,such as avoiding inbreeding depression and having flexible sexual allocation.But self-incompatibility still exists in hermaphrodite species.In the process of pollination and mating,hermaphrodite plants play both roles of pollen reception and pollen dispersal.It also brings about the potential conflict of female reproductive success,such as selfing,inbreeding depression or sexual interference.Although floral traits such as dichogamy and herkogamy can reduce the occurrence of the above problems,plants with larger floral displays still cannot avoid geitonogamy,that is,the existence of pollination of the same plant.As people gradually understand the male function,they begin to realize the conflict between male and female functions will not only affect the female function,but also bring a cost to the male reproductive success.In self-incompatible plants,the presence of self-pollen on stigmas may have some consequences.First,self-pollen may interfere with female function through stigma clogging,stylar clogging or usurpation of ovules,resulting in reduced fertility.Second,self-pollen on stigmas is not available for pollen export to other plants and may therefore reduce male siring success.We use self-incompatible monoecious Akebia species(Lardizabalaceae),to research the adaptive significance of self-incompatibility system in hermaphrodite plants,and the effect of geitonogamy on plants reproduction which have late-acting self-incompatibility systems.The effects of self-pollens on reproductive success were studied in order to reveal the adaptive significance of hermaphroditic plant sexual system,and to supplement the theory of plant sex interference and sexual phylogeny.The following aspects are studied in detail,and the results are below:First,geitonogamy is existed in Akebia.The data of male and female flowers and inflorescences of A.quinata and A.trifoliata was measured in the flowering period.Both A.quinata and A.trifoliata have strong sexual dimorphism.The inflorescences of different populations showed a large proportion of male flowers.Observation on the flowering phenology of A.quinata showed that the flowering periods of male and female flowers were overlapped.And it was found that the flower visitors were mainly flies,which were divided into two kinds: syrphid flies and house flies.Both syrphid flies and house flies were more likely to visit male flowers after male flowers.But the proportion of house flies visiting male flowers first and then female flowers was higher than that of syrphid flies.The pollinator's behavior and flowering phenology indicated that the geitonogamy is existed in Akebia.Second,different pollination order of self-pollens and cross-pollens don't affect the fruit setting of A.trifoliata.The mating system experiment and the pollen tube growth experiment showed that A.trifoliata is late-acting self-incompatibility plant,as well as A.quinata.Self-pollen can germinate and produce pollen tubes which can reach the ovule.Different pollination order of self-pollination and cross-pollination showed that the fruit setting is no significantly different between each other.Third,mixed pollen numbers and cross/self pollen ratio and their interaction effect reproductive success of A.quinata,and self-pollination can promote fruit set under certain conditions.The fruit setting rate of the four groups with different pollination ratios of self-and cross-pollen under the condition of sufficient or limited mixed pollination showed that self-pollens would reduce fruit setting rate in most cases.However,when mixed pollens were enough,a small amount of self-pollens could promote fruit setting,and self-pollens would not interfere with the production of seed setting.At the same time,the formation of mature fruit was affected by the critical number of fertilized ovule,and the fruit setting rate was significantly reduced under the condition of pollen limit pollination.