Studies On The Adaption Of Distyly Plant Luculia Pinceana And The Pollinator

The distylous plants are characteristic of two floral morphs(longand short-styled plants).It has been hypothesized that an adaptive strategy of distyly is to improve compatible pollination between floral morphs.The distylous plants usually rely on long-tongued pollinators to improve compatible pollination.The nectar and floral odour may affect pollinator behaviours and influence plant reproductive success.It remains unclear whether the nectar and floral odour of the distylous plants are adapted to the pollinators and promote compatible pollination.Luculia pinceana(Rubiaceae)is typically distylous,tubular flowers.Previous research showed that Apis florae was the effective pollinator of L.pinceana.According to the hypothesis that floral traits are mechanical fit to the pollinator body trait and the concepts of pollination syndrome,A.florae cannot pollinate the L.pinceana effectively,other than promoting the compatible pollination.Further research is needed to explore the type of effective pollinators of L.pinceana and whether the distylous L.pinceana promote compatible pollination,and how the nectar and floral odour are adapted to the pollinator behavior.The number of Long-styled morph(L-morph)and short-styled morph(S-morph)plants in the wild populations was counted.Floral traits of two morphs were measured.The number of legal(intermorph)and illegal(intramorph)pollen grains on the stigma in the field was counted.The germination rate and pollen tube length between intramorph and intermorph pollination treatments were compared.Different artificial pollination treatments were conducted to test whether L.pinceana was self-incompatible.The visiting insects were observed and the body sizes of effective pollinators were measured.Diurnal and nocturnal pollination treatments were conducted to test whether the L.pinceana needs nocturnal little animals for reproductive success.The nectar volume and sugar concentration during day and night of two morphs were measured.The nectar sugar composition of two morphs were analyzed with high performance liquid chromatography(HPLC).The floral odour during day and night of the two morphs was collected and analyzed using gas chromatography-mass spectrometry(GCMS).The behaviour preference of pollinators to the floral scent was determined by testing with a Y-type glass tube olfactometer.The main research results are as follows:(1)There is no significant difference in the plant number of L-and S-morph in the wild populations.The flowering period of L.pinceana usually lasted from June to December.There was no significant difference in the single flowering period(about 5 days)between L-and S-morph.The tube depth,tube diameter,opening diameter,stamen length and stigma length of L-morph were significantly lower than those of S-morph,while the leaf length,leaf width,pistil length,anther volume,pollen grain volume and stigma thickness of L-morph were significantly higher than those of S-morph.From the first day to the fifth day of flowering,the pollen viability of L-and S-morph decreased gradually.There was no significant difference of the stigma receptivity from the first day to the fourth day,but it decreased on the fifth day.(2)The proportion of legal pollen grains on natural stigma was significantly lower than that of illegal pollen grains.The pollen germination rate and pollen tube length of intermorph pollination were significantly larger than those of intramorph and mixed pollinations.The seed set of the intermorph pollination was significantly higher than that of intramorph pollination,and intramorph pollination treatment could produce some seeds.No matter the L-morph or the S-morph as pollen recipient,the seed sets between the intermorph and control pollination treatments were not significantly different,and they were significantly higher than that of intramorph pollination treatments.The seed set of selfand autogamy pollination in L-and S-morph flowers was also lower than that of the control treatment.The apomixis treatment of L.pinceana did not produce seeds.(3)The floral visitors of L.pinceana mainly contained hawkmoth(Cechenena lineosa),bumblebees(Bombus sp.)and honeybees(Apis).Among the three floral visitors,the visit frequency of nocturnal C.lineosa was lower than that of Bombus and Apis,while the nocturnal long-tongued C.Lineosa was an effective pollinator and its tongue was mechanical fit to the floral tube of L.pinceana.L.pinceana relies on nocturnal pollinators for intermorphic pollination.The Bombus and Apis mainly robbed the nectar.(4)The nectar volume was larger and the sugar concentration was lower at night than those during the day and the nectar volume and sugar concentration between the two morphs were not significantly different.The nectar was rich in sucrose.Floral odour composition was divided into7 different types: terpenes,alcohols,aldehydes,esters,acids,phenols,hydrazines and alkanes.The methyl benzoate is the highest chemical composition of the L.pinceana odour and the methyl benzoate content during the night was higher than that of the day.The methyl benzoate content between long-and short-morph is not significantly different.The C.lineosa shows a significant preference for it.The distyly L.pinceana achieved compatible pollination through the long-tongued hawkmoth C.lineosa,which was mechanical fit with its floral traits.It improved pollination accuracy through promoting intermorph pollen germination and pollen tube length.In addition,the nectar and floral odour traits of L.pinceana are adapted to the nocturnal long-tongued hawkmoth for pollination.The hawkmoth shows a significant preference for the floral odour.Plant-pollinator interactions improve the compatible pollination of heterostylous plants.This study provides a theoretical basis for the hypothesis that the adaptive strategy of distyly is to improve compatible pollination between floral morphs.