Research On Geitonogamous Selfing And Traits Evolution Of Aconitum Gymnandrum Maxim(ranunculaceae)

Mating system is critical for plant reproduction,and the evolution of mating system has important effects on ecology.Geitonogamy,as one of the mechanisms maintaining the mixed mating system,has been widely studied by researchers.Unlike most form of selfing,geitonogamy relied on the pollinator visiting and incorporated pollinator behavior into mating system evolution.In general,geitonogamy was considered to be inevitable of promoting and evolution of outcrossing,however,inbreeding depression,ovule discounting and pollen discounting make it cost for plant reproductive.So,how floral traits reducing geitonogamy through affecting pollinator behavior has been considered to promote the evolution of attractiveness traits,inflorescences architecture and self-incompatible.In adichogamy,researchers always focused on the fact that large floral display caused the increasing of geitonogamy by encourage pollinator visits more flowers within inflorescence and geitonogamy was higher in upper position of inflorescence caused by the upward movement behavior of pollinators.In dichogamy,researchers always considered the function of sex separation,such as protandry,in reducing of geitonogamy in inflorescence level.However,in dichogamy species,the among-and within-inflorescence pattern of geitonogamy and its reproductive consequence,the mechanism of how other floral traits,such as floral display,nectar characteristics,affect geitonogamy by influencing pollinator behavior were poorly understood.Moreover,we also known little about the role of geitonogamy on the evolution of plant attractiveness traits and self-incompatible.In this study,we measured geitonogamous selfing rate using microsatellite and quatified the phenotypic selection on floral traits through both female and male fitness.Moreove,we also explored the consequence of geitonogamy on reproductive and self-incompatible by carrying out hand-pollination experiments in filed.We explore following three mainly questions in protandry Aconitum gymnandrum: 1)what is among-and within-individual pattern of geitonogamy in Aconitum gymnandrum? Do floral traits affect geitonogamy through affecting pollinator behavior in Aconitum gymnandrum? 2)What is the relationship between floral traits and female and male fitness? Does the geitonogamy affect the selection on floral traits?3)Does the variation of geitonogamy affect the expression of self-compatibility among-and within-plant? Main results and conclusions in follow:1.In plant level,geitonogamous selfing rate was increased with large floral display of both main and lateral inflorescence,but reduced with decreasing nectar gradients that nectar volume reduced from bottom to top flowers.Geitonogamous selfing rate was higher in top flowers than bottom ones,and the number of unique fathers of seeds was also higher in bottom flowers than top flowers.In the hand-pollination experiment,our results showed that the pollen germination was lower in self-pollination treatment,but the fertilization rate and seedset was not difference between pollination treatment.Our results suggested that geitonogamy could be affected by floral traits which may reduce the cost of geitonogamy,promoting the stable of mixed mating system in Aconitum gymnandrum.2.Through female and male fitness,we quantified the phenotypic selection on floral traits.Our results showed that the evolution of floral traits was mainly caused by female rather than male fitness.Through female total(self+outcross)fitness,flower number was subject to a positive linear and a stabilizing selection,nectar volume was subject to a stabilizing selection,and nectar gradients was subjected to a negative linear and disruptive selection.Through both male and female outcrossing fitness,only nectar volume was subjected to a positive linear selection.There were no any other traits subjected to nature selection through male total or outcrossing fitness.With the increasing of flower number,the number of unique fathers,i.e.,pollen source,was decreased.The results suggested that pollen limitation may strengthen the selection on floral traits through female rather than male fitness.The stabilizing selection that detected on flower number and nectar volume showed the influence of geitonogamy on floral traits evolution.The difference of phenotypic selection imposed by different sexual function and fitness components(self vs outcross)may promote the diversified of floral traits and then affecting the ultimate evolution of floral traits of Aconitum gymnandrum.3.By hand-pollination experiments,we found no difference between crossand self-pollination treatment in pollen germination rate,length of longest pollen tube and mean pollen tube growth rate,which suggested self-compatible in pollen germination and tube growth stages.However,the pollen load on stigma was negative correlated with pollen germination rate,suggesting competition among pollen on stigma surface.The pollen germination rate at 4h after pollination was higher than at2 h,but mean pollen tube growth rate was higher at 2h,which suggested that the pollen was germinated and entry style in step and then strengthened the competition among tubes in style.The fertilization rate rather than seed set was significant different between cross-and self-pollination treatment,i.e.,fertilization rate was higher in cross-pollination treatment,suggesting a self-incompatible in fertilization stage.Moreover,the expression of self-incompatible was higher in bottom flowers that fertilization rate was higher in cross-than self-pollination treatment at bottom flowers but no difference between pollination treatment at top flowers,which may increase the reproductive fitness of individual.The flower number was not correlated with the fertilization stage self-incompatible,but decreased both the fertilization rate and seed set,showing more strict selection on male gametes for plants with more flowers,which may increase the seed quality.