A Preliminary Study On The Pollen Color Polymorphism And Pollination Ecology In Chamerion Angustifolium

Pollen grains are the male gametes of seed plants,which are transmitted from the male structure to the female structure surface by certain vector,and then fuse with the egg in the female gametophyte to achieve sexual reproduction.Pollen is rich in protein,and often consumed by insects,such as bees,beetles,and syrphid flies.The pollen of most plants is yellow,but rare in cream,orange,white,brown,black,red,or even blue or purple.In some plants,pollen color polymorphism exists in the wild population,providing an opportunity to explore the adaptation and variation in pollen color.Previous studies have suggested that colorful pollen is a visual signal for pollinators or the change in pollen color may reflect adaptation to heat and drought stress.Chamerion angustifolium(Onagraceae)is a perennial herb,and its pollen color is usually blue.We noted some individuals with yellow pollen in the field.To explore the adaptation and variation of pollen color polymorphisms,we conducted a preliminary study of pollination ecology and breeding system in this species.First,to understand the basic pollination ecology in C.angustifolium,we observed pollinator visits for two years,measured floral traits,observed and recorded the flowering phenology in the field.We also measured the nectar volume and concentration and conducted five pollination treatments.Floral visitors were diverse insects including Hymenoptera,Coleoptera and Lepidoptera.Among them,bumblebees were the most effective pollinators.Hermaphrodite flowers on racemose inflorescences were protandrous,characterized of movement herkogamy.A single flower had eight anthers,which pollen held together with short viscine threads and shed pollen sequentially.The model of pollen presentation may reduce loss during pollen delivery.Our pollination treatments showed that flowers under open-pollinated,intraplant selfing,hand and natural cross-pollination all yielded more than 60%fruit set and 50%seed set,but autogamy achieved significantly lower fruit and seed set.During its peak flowering period from July to August in Yunnan Province,southwest China,we observed that pollen grains from C.angustifolium were placed on the bumblebee bodies when they were sucking nectar,but not packed into corbiculae with grooming pollen behavior.Why bumblebee does not use pollen from C.angustifolium,which needs further study.Secondly,to test whether the maintenance of pollen color polymorphism could be driven by pollinator selection,we transplanted blue-pollen plants next to yellow-pollen plants to construct a mixed color pollen array and observed pollinator preferences and measured reflectance spectra of blue-and yellow-pollen flowers.Our preliminary results indicate that the yellow-pollen and blue-pollen had obvious reflection peaks in the wavelength range of 450-550nm,which could be visually susceptible by insects and provide short-distance visual signals to pollinators.The main pollinator groups preferred visiting plants with yellow pollen.We hypothesized that blue pollen might be less attractive,reducing the risk of pollen theft and loss.Future studies need to further compare the fitness differences between different pollen colors and study the genetic basis of pollen color polymorphism.