Floral Differentiation And Phenotypic Selection On Floral Traits Of Two Sympatric Relative Pedicularis Species

In nature,Angiosperms must rely on pollinators,like animals,water,wind,etc.,to achieve sexual reproduction.And pollinators have been considered as the main factor driving flower evolution.It is generally believed that pollinators with similar sensory preferences and pollination behavior will exert similar selection effects on plants.However,the Pedicularis of Orobanchaceae is a special case.Pedicularis is one of the largest genus of angiosperms in the northern temperate zone,with more than 600 species worldwide.The mating system of this genus is dominated by obligate heterosis.Many species are often sympatric,and the flowering time overlaps.The Bombus are mainly effective pollinators,and the sympatric species are usually pollinated by the same species of bumblebee.But corolla types of different species,especially the shape of the corolla tube and the upper lip,show a great variation.We divide the corolla types of Pedicularis into short and long tubes,according to different types of rewards.For these two corolla types,we selected Pedicularis kansuensis Maxim.and Pedicularis semitorta Maxim.as the research materials.We calculated the plant height and inflorescence number,and measured the floral traits related to pollinationof the two species for two consecutive years.We estimated the intensity of phenotypic selection on floral traits using female fitness(seed number),and compared the difference between two pedicularis species and between different color of P.kansuensis.The result showed that:(1)In general,there were significant correlations among floral traits of the two Pedicularis.For P.kansuensis,we found significant correlation among nectar depth,floral size and style length,which is consistent in different year.It indicated that the evolution and function of these traits may be highly integrated.For P.semitorta,there was significant correlation among beak length,style length and floral size,but the correlation between beak length and other floral traits has significant change in different year.(2)There were significant different on phenotypic morphology and nectar volume between different color of P.kansuensis.P.kansuensis f.albiflora have bigger floral sizes,and longer style length,but it's inflorescence number,nectar volume and sugar content were lower.And,P.kansuensis f.albiflora have a lower pollinationefficiency than P.kansuensis.The result also showed that the individuals with a big corolla had low pollination efficiency.It may be due to the fact that the larger corolla is associated with a lower fit with the body of Bombus.But there was no significant correlation between floral traits and pollination efficiency.(3)The selection on inflorescence number of P.kansuensis were significant,indicating that individuals with more inflorescence have higher female fitness(more seed numbers).For P.kansuensis f.albiflora,there was significant selection on inflorescence number,floral size,style length and nectar depth.And there was also significant selection on nectar volume and sugar content.P.kansuensis with both colors ensure seed numbers with different floral traits.So the differentiation of floral color may be an approach for plants to improve their fitness and ensure reproduction.(4)The selection on inflorescence number of the two species were significant,and stay consistent in different year.For P.semitorta,the phenotypic selection on inflorescence number,plant height and style length were significant,but the phenotypic selection on floral size and style length was not significant always.Especially beak length was not be chosen,that is,had no effect on female fitness.We speculate that it may be related to pollen diffusion by pollinator-mediated(male fitness).(5)There were correlation selection of P.kansuensis f.albiflora and P.semitorta.For P.kansuensis f.albiflora,the result showed that inflorescence number and floral size or nectar depth or plant height were significant selected,and may affect female fitness nonadditively.For P.semitorta,the result showed that inflorescence number and style length or plant height were significant selected,and may affect female fitness nonadditively.Functional integration of flowers is assumed to be a product of correlational selection,and this result provide a new experimental approaches can advance our understanding of the evolution of trait combination.In summary,there were significant differences in floral traits between P.kansuensis and P.kansuensis f.albiflora,but the P.kansuensis has higher pollination efficiency,while P.kansuensis f.albiflora have higher female fitness.For both corolla types,more flowering numbers are the main strategy for Pedicularis to ensure individual seed numbers.The intensity of the phenotypic selection and correlationselection for two Pediularis species showed variation in different year.And the variation will influence the evolution of corolla morphology.