Study On Adaptive Evolution Of Floral Traits In Mazus Species

Genus Mazus is an annual or perennial herb,which belongs to Mazaceae.The Mazus species have labiate,white or purple flowers and 4 stamens and bilobed stigmas which will close together after being touched by pollinators in a short time and are also called the sensitive stigma.There is great variation of floral traits in different Mazus species.Although there are some researches about the breeding system of Mazus species,there is a shortage of research about the adaptive evolution of floral traits in Mazus species.So our research will be focused on following 3aspects:(1)By constructing the phylogenetic tree of Mazus,we analysed how Mazus species might have migrated and whether there was any correlation between floral traits and phylogenetic relationship of Mazus.(2)What kind of correlation does there exist between stigma sensitivity and floral traits of Mazus species?(3)What kind of sexual resources allocation does there exist in Mazus? By answering several above questions,we aim to fill some gaps in the study of adaptive evolution of floral traits and provide new evidence of adaption evolution of plants.There are 27 species in Mazus,mostly distributed in Asia and some parts of Oceania.Although there are some researches about the phylogenetic relationship of some Mazus species.These are only a small part of whole genus,which can't clearly illuminate the phylogenetic relationship of most of Mazus species.And there is no research which combines phylogenetic relationship,geographic distribution and floral traits of Mazus together to reveal the migrating route of Mazus species and evolutionary pattern of floral traits.To achieve these,we downloaded some DNA data of Mazus from NCBI and gathered some molecular materials of Mazus from field.The phylogenetic tree of Mazus was constructed and also analyzed together with geographic distribution and floral traits.The results showed that there was a tendency of migrating route of Mazus,that is from Australia to Asia and from west China to east China.There were also some differences between various species in stigma sensitivity,corolla size and flower color.But there didn't show any principle of these traits along with the phylogenetic route.So it might be the local adaption for habitats.Stigma sensitivity has been recognized to be an important floral trait which can significantly influence plant pollination and mating system composition.But the relationship between this trait and other floral traits affecting pollination process needs to be studied intensively.In order to better understand the evolutionary pattern of sensitive stigma and explore the adaptive evolutionary relationship between stigma sensitivity mediated by pollination and floral traits,three Mazus species,that is M.spicatus Vaniot,M.longipes Bonati and M.stachydifolius(Turcz.)Maxim.in different pollination environment and with significantly different floral structures were selected in our study.By observing stigma behaviors and measuring floral traits,the relationship between them were analyzed.Results indicated that under same stimulation,M.spicatus Vaniot was the least sensitive(longest stigma closing time),followed by M.longipes Bonati mid sensitive,while M.stachydifolius(Turcz.)Maxim.was the most sensitive.The results also showed that for floral traits,such as flower color,single flower display,anther stigma separation and pollen-ovule ratio,three Mazus species showed significant differences.Compared to M.spicatus Vaniot and M.longipes Bonati with weaker stigma sensitivity,M.stachydifolius(Turcz.)Maxim.with stronger stigma sensitivity had purple flowers,bigger single flower display area,longer anther-stigma separation and bigger pollen-ovule ratio.Our study indicated that the evolution of stigma sensitivity of Mazus might be closely linked with floral traits which influence pollinator attraction,pollen loads,pollen delivering efficiency and composition pattern of plant mating system.According to the sexual allocation theory of plants,there should exist trade-off between resource investment for sexual function of plants.There is great difference of sexual functional traits in various Mazus species,with diverse breeding system patterns.To investigate how plants allocate resources to different sexual function,we chose 11 Mazus species and investigate their sexual functional traits and floral traits and analyzed the relationship between those traits.The results demonstrated as follows:(1)there is a positive relationship between corolla size and male functional traits in Mazus.(2)there is a positive relationship between P/O and corolla size andpollen size in Mazus.(3)there is a positive relationship between style length and pollen size in Mazus.(4)there is a positive relationship between pollen number and ovule number,and a positive relationship between pollen number and pollen size.The above results showed that there didn't exist expected trade-off between resource investment for sexual function of Mazus species for genetic or ecological reasons,and these provided a new material for researching sexual functional allocation of plants.