A Preliminary Study Of Pollination Mechanisms In Aspidistra Species(Asparagaceae)

The genus of Aspidistra,a species-rich(more than 100 species),belongs to Asparagaceae(Monocotyledoneae),its distribution and differentiation center locating in Guangxi Province,south China and North Vietnam.How does a diversity of Aspidistra species form in this narrow area?Unlike most angiosperms,flowers in Aspidistra species usually grow near ground level,covered by fallen leaves,these cryptic flowers without nectar or prominent petals.Benefit for leaves are clustered and evergreen,some species have been transplanted widely and cultivated in garden.The reproductive ecology of Aspidistra species,however,is little known.To explore reproductive strategies in Aspidistra,and to figure out how the inconspicuous flower attract pollinators,we investigated pollination mechanisms in three Aspidistra species in Guangxi.This project is mainly focusing on pollination ecology in Aspidistra species.Pollination process in three species Aspidistra saxicola,Aspidistra retusa and Aspidistra longipetala were studied.We recorded flowering phenology,pollinator visiting frequencies and foraging behavior,especially measured flower temperature and spectra reflectance,floral odor components and breeding systems in the field populations.We observed that the gall midge(Cecidomyiidae)was pollinators for A.retusa and A.saxicola,which larvae consumed pollen and mature insects carried pollen of Aspidistra species.Sex ratio of the gall midges caught on the Aspidistra flowers was all female biased.Our results indicated that gall midges performed both pollination and oviposition behavior.Fungus gnats(Mycetophilidae)were effective pollinators for A.longipetala,which visit flowers shortly.Interestingly,A.longipetala released odors that smelt like mushrooms,which the base of corollas had very high reflectance.Neither insect eggs nor eggs larvae of fungus gnats were observed in flowers of A.longipetala.Therefore,A.longipetala was likely to involve a deceptive mimicry pollination.While various insects,including solitary bees(Halictus)and syrphid flies(Syrphidae)visited flowers of Aspidistra dolichanthera.No obvious difference was observed between flowers temperature and ambient temperature in A.saxicola,indicating that this species were not thermogenic.Spectrum reflectance analysis showed that swelling stigmas with bright colors had UV band reflection,combining with other flower parts relative strong reflection which may serve as a visual signal to fly visitors.Our GC-MS analysis identified similar flower volatile that appear in other odor mimicry system,indicating A.saxicola with(pinene,camphene,3-ethyl acetophenone,?-caryophyllene etc.),A.longipetala with(2-ethyl-hexanol,2-hexyl-1-decyl alcohol,ethyl acetophenone,2-methyl-ethyl butyrate etc.),and Aspidistra retusa with(a-olefin guanidine,camphene,limonene,2-?-pinene etc.).Our hand pollination treatments showed that the investigated species were all self-incompatible and no autonomous pollination,indicating that sexual reproduction is dependent on pollen delivery.No pollen limitation was observed in Aspidistra saxicola,Aspidistra longipetala or in A.retusa.Field fruit set was significantly different between different Aspidistra species,likely resulting from availability of pollinators.Seed set in A.retusa under hand cross-pollination was significantly different between 2016 and 2017 at Yanshan site,likely caused by the fluctuation of inter-annual floral resource.Our two years field study showed a variety of pollination systems in the genus Aspidistra,and female gall midge lagged eggs on flowers,later developing into larvae which feed on fertile pollen.A.longipetala released odors that smelt like mushrooms,probability to attract fungus gnats.Our preliminary investigation of pollination systems in Aspidistra provides insights into species diversification in a group of plants with cryptic flowers.