One-by-one Stamen Movement And Reproductive Isolation Of Parnassia

Parnassia L.has the phenomenon of stamens moving one by one actively and releasing pollens,which called “one-by-one stamen movement” may be an important factor in the specialized pollination and speciation of this genus.In this paper,P.perciliata,P.wightiana and P.amoena from Jinfo Mountain(Chongqing)were studied,combined with the phenology and micro-habitat,the pattern of stamen movement,petal reflectivity,pollination process and other aspects to analysis the possible role of one-by-one stamen movement in pollination isolation and species differentiation of three Parnassia species.At the same time,two new species of Parnassia were found in Chongqing mountainous area and were published by us.The result is as follows:(1)P.wightiana and P.amoena are sympatric,grow in the north slope of Jinfo Mountain at an altitude of 1900 m.The population of P.wightiana is mostly distributed in wet soil,P.amoena prefers water-rich areas,which grow on the rocks where streams and waterfalls drop water.P.perciliata is distributed 23 kilometers away under the Shibangou waterfall,there is obvious geographical isolation.The pollen of P.amoena had the highest water resistance,which could keep 92 h activity in water,while that of P.wightiana and P.perciliata could keep 47 h and 36 h respectively.(2)The flowering period of P.perciliata is from July to August,and that of P.wightiana is from July to September,while P.amoena is mainly flowering from August to September.The blossom period of sympatric P.wightiana and P.amoena is in late August and late September respectively.The staggering of blossom period is beneficial to the reproductive isolation of species.(3)The first stamen of P.wightiana,P.amoena and P.perciliata began to elongate respectively at 292±14min,289±18min and 213±2min after petal opening;the time for the filament to reach its maximum length is 1497±63 min,2155±136min,1391±28min after petal opening,respectively;time for a stamen to begin its filament deflexion after the start of anther dehiscence is 292±18min?313±12min?352±13min after the anther is at the flower center.The time for the next stamen to begin its filament elongation after the start of the former stamen's anther dehiscence is 251±9min?325±21min?256±9min respectively.Among the three species,the stamen movement speed of P.perciliata is the fastest,while the slowest speed of stamen movement is P.amoena.(4)The flowers of the three species are large,protandry and herkogamy,thus the outcrossing index is as high as 5.The ratio of pollen and ovule of P.perciliata is 633±25,which was much higher than P/O of P.wightiana(309±22)and P.amoena(324±39).The percentage of seed set of sympatric P.wightiana and P.amoena was lower than 3% after artificial interspecific hybridization,which indicated that there was reproductive isolation between them.(5)The main flower visiting insects of the three species are large aphid flies and small flies.The color coding results of petal reflectance conversion show that the color of P.wightiana,P.amoena and P.perciliata belong to the same color quadrant in pollination insect perspective,but P.amoena is relatively bright,and P.wightiana is the darkest.(6)Based on the comparison of all model specimens and literature,two new species of Parnassia were identified by morphological identification.P.zhengyuana M.X.Ren &J.Zhang,sp.nov.grow in a limestone cave in Jinfo Mountain,Nanchuan District,Chongqing.This species has a special spoon-shaped leaf and the top of staminode is green and dose not lobed.P.simianshanensis M.X.Ren,J.Zhang & Z.Y.Liu,sp.nov.growing beside the stream on the red sandstone of Danxia Landform in Simian Mountain,Jiangjin County,Chongqing.This species has special rhombic leaves and 5-lobed deeply staminodes.The discovery of these two new species provides strong evidence for the role of habitat isolation in promoting speciation.In summury,one-by-one stamen movement among Parnassia species may be an evolutionary consequence of adaptation to pollinators,such as aphid flies and flies,which have low pollination efficiency but high flower visiting frequency.And it is also a strategy to improve pollen export.Different stamen movement pattern,different flowering period and cross incompatibility are important reasons for speciation and maintenance.