| Swertia has actinomorphic corolla lobed to base,with short corolla tube,showing obvious generalization pollination syndrome.Different to general generalization pollination groups,Swertia has a variety of nectaries located on the petals.These specialized nectaries may probably play an important role in insect pollination process.Nectaries of Swertia can be divided into two types:fimbriate ones and naked ones-gland patch,according to the morphology.Fimbriate nectaries are usually located at the base of the corolla lobes,and gland patches are mostly occured in the middle of the corolla lobes.There were few reports that researched the pollination ecology of Swertia,most of these reports did not pay enough attention to the relationship between pollination and nectaries,and no research of species that possess gland patches were reported yet.Although some studies regarding the nectaries of this genus had been made,they were restricted to morphology and taxonomy,with no combination to pollination experiments.In order to further understand the evolution of nectaries in Swertia,we carried out the experiment.In this study,we selected two Swertia species grown in the same place——Swertia bimaculata and S.kouitchensis as objects,the nectaries of which were gland patches and fimbriate ones respectively.We carried out experiments about floral traits,mating patterns,nectary traits and insect visitors.The results are shown below:1.Floral traitsFloral morphology For Swertia bimaculata,the diameter of monoclinous flower corolla averaged 25.67 ± 3.74mm,the diameter of nectary whorl averaged 14.05 ±2.18mm,stamen length averaged 5.60 ± 0.59mm,and pistil length averaged 6.03 ±1.13mm.The androecium diameter averaged 8.2 ± 2.3mm in the male stage,and 12.5 ±1.6mm mm in the female stage,there's significant difference between them.There were some female flowers found in S.bimaculata,and these flowers were smaller than monoclinous flowers in corolla diameter,nectary whorl diameter and pistil length.For S.kouitchensis,corolla diameter averaged 15.8 ± 1.3mm.the diameter of nectary whorl averaged 3.2 ± 0,2mm,stamen length 4.2 ± 0.3mm,pistil length 4.2 ± 0.4mm,the androecium diameter 3.6 ± 0.6mm,stamens movement was weak.Anthesis For S.bimaculata,the anthesis from corolla opening to corolla closure lasted for 5.44 ± 1.25d in total.From corolla opening to anther dehiscence lasted 0.87 ±0.76h.Pollen dispending lasted 0.50 ± 0.49d.Since the pollen depletion to stigma exposure lasted for 1.01 ± 0.38d.And stigma receptiveness lasted 2.05 ± 0.63d.S.kouitchensis had an anthesis last for less than Id,anthers dehiscence usually accompanied by corolla opening,and with stigma exposure at the same time of anther dehiscence,there is no obvious dichogamy.Flowering pattern Consider individual as a unit,the average daily opening flowers of S.bimaculata was 6.1,which include 2.6 monoclinous flowers in the male stage,2.4 monoclinous flowers in the female stage,and 0.9 female flowers.The number of opening flowers each day showed a skewed distribution among individuals,a few flowering plants had much higher flowers than the majority of population.The average daily number of open flowers had a significant positively correlation to plant height.Within the population female flowers accounted for 9.7 ± 3.30%.There was no clear upward or downward trend for number and proportion of female flowers within the population going along with the date.Female flower proportions varied strongly between plants,also showed a skewed distribution,but had no significant correlation to the numbers of flowers opened daily or plant heights.The current number of opening flowers on a S.kouitchensis plant averaged 11.7.No significant skewness was observed.2.Matting patternsPollen dispending experiments After bagging spent 1 days later,there was no significant reduction in the number of pollen on the anthers,and the natural shedding of flowers after 0.3 days,pollen has been basically completed the bulk.These results suggest that if S.bimaculata anthers isolated pollinators,you can not complete the loose,and S.bimaculata under natural conditions anther can be done quickly and thoroughly loose.Wind,gravity and other effects for S.bimaculata pollination effect is minimal,there must be complete pollinating insects visiting flowers participation.Investigation of stigma pollinated rate The stigma pollinated rate of S.bimaculata was 91.1%for bisexual flowers,and 80.0%for female flowers.Pollen-Ovule ratio Total pollen grains number in a monoclinous flower of S.bimaculata was 86355 ± 26618,and ovules number 95 ± 25,the pollen-ovule ratio was 912 ± 171.The ovule number in a female flower of S.bimaculata is 47 ± 10,significantly less than monoclinous flowers.AS.kouitchensis flower had 8072 ± 1513 pollen grains,and 170 ± 42 ovules,the pollen-ovule ratio was 49.2 ± 11.5.Fruit set and seed set Emasculation and bagging S.bimaculata flowers did not set fruit,indicating the absence of apomixis.Only a few bagged bisexual flowers set fruit,the overall seed set coefficient was 20.3 ± 32.70%,but the bags was likely acted as pollinators.After emasculation natural pollination of bisexual flowers,all the seed,seed set rate was 82.2 ± 15.7%,natural pollination of bisexual flowers,almost all the seed,seed set rate was 83.2 ± 22.6%,seed set rate between the two had no significant difference,indicating emasculation had no significant influence to S.bimaculata pollination process.Granted to the same strain of artificial pollen bisexual flowers,all the seed,seed rate was 83.8 ± 27.7%,granted to dioecious artificial pollen bisexual flowers,are all strong,seed rate was 77.0 ± 17.8%,and between the two there was no significant difference,indicating S.bimaculata is completely self-capable.The rate of natural pollination seed treatment groups was not significantly lower than that granted to a sufficient amount of artificial pollen treated,therefore,in S.bimaculata experiment populations there is no obvious limit pollen.The free-pollinated female flowers all set fruits,the seed set rate was 94.3 ± 8.30%,significantly higher than the bisexual flowers.S.kouitchensis bagged seed group was 4.7%seed rate was 0.7 ± 3.9%.Emasculation strong group was 7.7%seed rate was 5.1 ± 18.2%.Fruit set of natural pollination group was 40.0%,seed set rate was 32.0± 43.6%.Three sets of data compared to natural pollination or seed setting rate regardless group were significantly higher than group emasculation and bagging group.Only from flower drugs and pollinators exist,S.kouitchensis to get more substantial solid and seed,so it can be confirmed that,S.kouitchensis anthers and insect visitors had a significant synergistic effect,under natural conditions,the main part of S.kouitchensis mating pattern was insect-assisted self-pollination.3.Nectary featuresSurface structure A S.bimaculata gland patch has a flat appearance,morphology and surface area spot gland cells corolla surface is very similar to other regions.These epithelial cells showed papillary,the outer surface of the mastoid clouds longitudinal ridges adjacent mastoid distance between about 10 to 20?m.Such micro-structure is very similar to the lotus leaf surface morphology,it might have the "lotus effect",making nectar on the surface of the corolla tend to aggregate into droplets attached to the gland at the spot,rather than overspill outside petals.S.kouitchensis and most belong to the same species,has a concave shape of the crypt,crypt edge has long tassels.S.kouitchensis nectaries and corolla lobes do not have a similar papillae structure like S.bimaculata.Gland patch's effect on insects Gland spot removal did not significantly reduce the number of visiting insects,but insects take only a single residence time was significantly shortened.The results show that the gland patches did not have a decisive effect in the single flowers attract insects visual aspect,but it provides compensation feature makes it longer excitation insects play a vital task to spend to stay in role.Nectar secretion For a bisexual flower of S.bimaculata,the duration of nectar secretion total lasted for 4.9 ± 1.6d.The total amount of nectar secretion single flower spent the entire period was 57.2 ± 29.(?l,wherein the total amount of secretion of the male stage 26.8 ± 11.6?l,the total amount of estrogen secretion phase was 28.1 ± 22.3?l.Single flower single-day volume of nectar was 10.5 ± 7.4?l,wherein the male stage in a single day was 13.9 ± 8.O?l,female single-day stage was 8.5± 6.2?l,much higher than the male stage estrogen phase.Single flowering spend the most amount of nectar secreted first day,after day in descending order.From the fourth day,we have started a few single flowers without nectar secretion,to 6 days,more than half of existing single flower no longer secrete nectar.Female flowers honey production speed is far less than bisexual flowers.Swertia cauliflower honey sugar concentration was 7.6 ± 4.1%,in the male stage 10.8±4.2%,female stage is 6.2 ± 3.1%,much higher than the male phase estrogen phase.Flowering flower honey initial concentration of 2 may high to the third day there is a significant drop,decreasing the overall trend in the future.Swertia spend a single day menu secreted sugar component of 0.84 ± 0.77mg,male stage a one-day sugar component of 1.41 ± 0.88mg,female stage is 0.59 ± 0.57mg,much higher than the male stage estrogen phase.The total amount of sugar secreted S.bimaculata for the period spent spent 4.97 ± 2.61mg.S.kouichensis nectar secretion is very meager,and difficult to measure.4.Insect pollinationInsect species and behaviour Insect visitors of S.bimaculata ranged up to more than 35,mostly Diptera and Hymenoptera,a handful of Hemiptera,Lepidoptera,Coleoptera and other categories.Almost all insects that visited S.bimaculata flowers when feeding on nectar in the corolla had "circling" behavior.Most of the "circling" in the form of insects crawling between the petals,the tangential direction of the long axis of the body when crawling and gland ring spot remained roughly the same,so we will take the honey acts as "typical" behavior.A few species used flight mode from one movement to the next petal.Opportunity S.bimaculata pollinators visit flowers size and when used in contact with anther behavior is closely related to size.Insect feeding on pollen behavior S.bimaculata cauliflower is very rare.The number of species of pollinators of S.kouitchensis was far less than S.bimaculata,recorded only about 13 species,most of which are Hymenoptera and Diptera,other categories were observed very occasionally.Visiting frequency Visiting events of S.bimaculata populations had 56%from bees,and 42%from flies.In the S.kouitchensis population,visiting events from bees was 76%,and flies 23%.Fly visitors of S.bimaculata was significantly more than the proportion of S.kouitchensis.A period spent in S.bimaculata bisexual flowers visited a frequency of 17.1 times/h.Wherein a higher stage in the male flowers of the respondents frequency of 21.4 times/h,while the female gender stage perianth visit frequency is only 13.2 times/h.The female is much lower than the frequency of visits bisexual period,only 4.2 times/h.Bee visiting frequency of S.bimaculata was slightly higher than the flies.S.kouitchensis flower is much lower than the frequency of visits Swertia,only 2.9 times/h.Bees and flies visiting frequencies in S.kouitchensis were 2.2 times/h and 0.7 times/h.Handling time and the number of petals passed Not frightened insect individuals S.bimaculata take a male gender stage residence time of 19.8 ± 1.2s,take in a female gender stage residence time of 15.1 ± 1.Os,while staying in a female only 8.9 ±1.5s,three showed a significant decrement relationship.Flies individual residence time is slightly longer than the bees.Each insect taxa take residence time distribution radiate strongly skewed,far higher than the average of the median,skewness of the only large flies is not so strong.The number of individual insects petals not frightened when visiting a male hermaphrodite flowers are passing phase for 4.6 ± 0.15,the number of petals when accessing female bisexual flowers are passing phase for 4.1 ± 0.13,the number of female flower petals when accessing the passing 4.2± 0.43.Between different categories of flowers,the petals of the number of passing insects difference is not as insects dwell time difference as poor.The average number of bee individuals passing through the petals was more than flies.Skewness insects passing petal number distribution is less than the residence time as strong.Insect individuals on S.kouitchensis flowers spent average 22.5 ± 6.4s,the number of petals passed was 4.8 ±0.4.Pollination efficiency The results show that in the S.bimaculata populations,pollinating contribution of flies was significantly higher than bees,that is,by the completion of effective flies spend significantly more than the bees visit.Of S.bimaculata bisexual flowers,the effective completion of flower-visiting the event are mainly those of larger size categories.Contribution of large fly populations was significantly higher than that of large bees,and even higher than bees.Fly pollination individual stability and efficiency index was significantly higher than that of individual bees,and in bisexual flowers,large flies individual index far higher than the average level of flies,and also much higher than large bees.Based on the above comparison,it can be considered that in individual pollination efficiency,large flies were far better than other groups.In S.kouitchensis populations,pollination efficiency of flies was slightly higher than bees at the individual level,but because of the lower visiting frequency,they contributed less than bees at the population level.At group level,the pollination efficiency of S.bimaculata visitors was much higher than S.kouitchensis visitors. |
PDF Full Text Request