Floral scent variation in plants : pollinator attraction strategy dependent of display size

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To examine the contribution of diurnal and nocturnal pollination to male and female reproductive success in Lilium auratum, we conducted diurnal and nocturnal pollinator exclusion experiments and also analyzed floral scent. We found that either diurnal or nocturnal pollinators result in female reproductive success in L.auratum : there was no significant difference in the seed : ovule ratios among the flowers in which only diurnal pollination was allowed, those in which only nocturnal pollination was allowed, and the control flowers. However, plants required both diurnal and nocturnal pollinators for male reproductive success : the numbers of pollen grains remaining in both diurnal- and nocturnal-treated flowers were significantly greater than those in the control flowers. The total amount of floral volatiles of L.auratum showed a time-series rhythmic pattern, namely, they were significantly higher at night than during the day and gradually decreased with flower age. At night, the total amount of floral volatiles peaked on the second day from anthesis and subsequently gradually decreased with flower age. During daytime, the total amount of floral volatiles was constantly low. The composition of floral scent of all time-series examined was mostly isoprenoids, which often served as an attractant of the nocturnal hawkmoth, and there were less fatty acid-derivatives, which often attract diurnal pollinators. The floral scent composition also showed time-series changes, but Sorensen's similarity indices indicated that nocturnal scent might maintain a more constant composition with flower age than diurnal scent. Thus, such nocturnally biased floral scent emission of L.auratum might exist to fulfill male reproductive success by attracting nocturnal pollinators, and its visual cues might serve to fulfill male reproductive success by attracting diurnal pollinators. This may suggest that floral scent of this species plays a role in male reproductive success, as do visual cues.