Adaptive Significance Of Floral Color Change In Clematis Akebioides

Flower is the reproductive organ of angiosperms,its color with extremely diversity.Flower color changes during flowering in some species.The study of flower color change is helpful of understanding the adaptation of floral traits.Previous studies have proposed three hypothesis of several ecological functions of floral color change:(1)improve efficiency hypothesis:old flowers(without no more rewards)changed color,so that pollinators avoid visiting color changed flowers but increase visiting.newly opened,un-pollinated flowers,thus increasing both foraging and pollination efficiency;(2)reduce geitonogamy hypothesis:inflorescences with color-changed flowers could increase floral display size and the attraction to pollinators,and reduce visiting time by a pollinator thereby avoid geitonogamy;(3)avoid reproductive interference hypothesis:inflorescences with color-changed flowers could not increase attraction but instead avoid the interference of unnecessary visits,thus provide protection to post-pollination events(pollen tube growth,the formation of ovules embryos).To explore the adaptive significance of flower color change,here we used a woody climber Clematis akebioides(Ranunculaceae)as a model system to conduct below investigations.Species in Ranunculaceae varied in calyx and petal,amongst which Clematis species have only calyx as perianth.Clematis akebioides is a perennial vine,its calyx would change the color from yellow to red during anthesis.To test the improve efficiency hypothesis,reduce geitonogamy hypothesis and avoid reproductive interference,we measured floral characteristics including nectar volume and concentration,the optical reflectance of calyx in different flowering periods,pollinator visiting preference,artificial pollination,etc.The following questions were answered:(1)Which floral traits would change as the color changed?(2)Would flower color change affect pollinator's visiting preference or other behaviors?(3)Did Clematis akebioides have pollen limitation or inbreeding depression?Results:(1)Clematis akebioides flowers secreted the largest volume and highest concentration when in yellow-color phase but not in red-color phase;the analysis in the optical reflectance of flower color indicated that flower color change can be perceived by bumblebee pollinators.Artificial pollination could reduce the lasting time of yellow calyx that accelerating the speed of color changing.(2)Bumblebees preferred to visit yellow-colored flowers and rarely visited red flowers.(3)In the observational population,there was no significant difference between natural seed set and artificial pollination,suggesting no pollen limitation;but self-pollination seed set was lower than outcross pollination,indicating that Clematis akebioides had weak inbreeding depression.The results showed that,pollination could accelerate the speed of flower color change in Clematis akebioides.The flower color change in this species was not the byproduct of flower senescence,but the biochemistry process that the calyx losing the function of photosynthesis and synthesizing anthocyanin to make the old flower present in red color.The red old flower could induce pollinators to newly open flowers instead of the unnecessary visits to pollinated flowers,increasing foraging and pollination efficiency in single inflorescence,accord with improve efficiency hypothesis and reduce geitonogamy hypothesis.In combination with the changing of floral traits,pollinator responses and the consequences of pollination,we studied the reason and adaptive significance of flower color change in Clematis akebioides.The work in this M.D thesis laid foundation to a deeper understanding of plant-pollinator interaction and the mechanism of flower color change,and provided references to horticulture and gardening in developing breeds with various colors.