Temporal variation in floral display size and individual floral sex allocation in racemes of Narthecium asiaticum (Liliaceae)

We analyzed the effects of temporal variation in floral display size (number of flowers open at one time on a plant) on the rate of pollen removed and receipt of individual flowers for the sequential blooming plant Narthecium asiaticum (Liliaceae). Because of the acropetal blooming of this species, the display sizes when upper flowers opened was much greater than the display sizes when lower flowers opened. Our experiments revealed that large displays lead to a high rate of pollen removal from individual flowers, though they do not lead to a high rate of ovule fertilization. Consequently, the rate of pollen grains removed per flower by pollinators was greater in upper flowers than in lower flowers. The pattern of sex allocation in individual flowers within a raceme was consistent with such variation. Namely, both maleness [stamen mass/(stamen mass + pistil mass)] and pollen : ovule ratio were larger in upper flowers. We suggest that the temporal variation in display size, in addition to such factors as dichogamy and pollinator directionality, also produces variation in the probability of successful pollen transfer from individual flowers that may cause the variation in the sex allocation of individual flowers.