Effects of floral sexual investment and dichogamy on floral longevity

Aims Floral longevity,the duration that a flower remains open and func-tional,varies greatly among species.Variation in floral longevity has been considered to be optimal strategy for resource allocation under different ecological conditions,mainly determined by the rates of pollination and cost of flower maintenance.However,it is unclear whether an intrinsic factor,floral sexual investment,con-strains evolution of floral longevity.The theoretical model also pre-dicts that dichogamy favors long-lived flowers,but empirical studies to test this prediction remain unexplored.Methods To examine the effect of floral sexual investment on floral longevity,we measured flower size together with pollen and ovule production in 37 sympatric flowering plants in a natural community.The duration of the female and male phase in 21 protandrous species and floral longevity of the other 16 adichogamous species were documented in the field.Important Findings Floral longevity varied from 1 day to 15 days,while pollen num-ber per flower varied from 643 to 710880 and ovule number per flower from 1 to 426 in the 37 species.Flower size was corre-lated with pollen production as well as ovule production.Floral longevity was positively related to pollen production but not to ovule production.Consistent with the prediction that dichogamy favors long-lived flowers,we found the floral longevity of pro-tandrous species was significantly longer than that of adichoga-mous species.in the protandrous species,pollen production per flower was observed to be positively related to male duration,while ovule production was not related to female duration.our analyses of variation in floral longevity and sexual investment among different species suggest that the floral sexual investment could be an intrinsic factor contributing to the selected floral longevity,particularly the male phase,and that high pollen pro-duction could potentially increase pollen removal,i.e.male pro-ductive success.

Evidence of Dichogamy in Santalum album L.

Flowering, fruit set, embryological development, and pollination trials were Investigated In Santslum album L. Each ovary may have three to four ovules. Mlcrosporogenesls and megasporogenesls In the same flower were synchronized at the earlier stages of flower development. However, at anthesls, when pollen was mature, the magaspore had developed only to the stage of a one- to two-nucleus embryo sac. As the eight-nucleus embryo sac developed, some mamelon cells began to undergo programmed cell death, forming holes Into which the eight-nucleus embryo sacs extended, becoming ＂N＂ or ＂S＂ shaped. The development from a two-nucleus embryo sac to a matured eight-nucleus embryo sac lasted up to 10 d. Fruit-set from open pollination was less than 2%. The endosperm develops prior to division of the zygotic embryo and one to three embryos and endosperms were formed In the same fruit. A mature seed usually germinates to produce one seedling; however, two and three seedlings from one seed were also observed, albeit at a low frequency. Pollination trials showed that no seed sets when Inflorescences were covered with s bag; however, artificial pollination could Improve fruit set. Our pollinaUon trials and embryological studies proved that the flower of S. album Is dlchogamous and fruit set has high heterozygosity.

Sexual and Breeding Systems in a Xerophytic Shrubland

Reproductive systems are fundamental attributes for understanding life cycle and regeneration processes and provide information about seed production and genetic diversity. Analyses of reproductive strategies within communities and their associations with functional groups can indicate how physical and biological characteristics may influence the reproductive ecology of such communities. The main goal was to determine if the reproductive systems and their associated functional groups have particular characteristics related to extreme conditions and disturbance within xerophytic shrubland. Floral morphology analysis and four experimental tests were conducted to determine the reproductive systems of species and their associations with the life form, succulence, carbon metabolism, dispersal syndrome, pollination, and disturbance. Of the 144 plant species studied, 72.9% were hermaphrodite, 22.9% were monoecious, and 4.2% were dioecious. Dioecy was associated with woodiness, frugivory and undisturbed areas, while monoecy was more common in herbs. Adichogamy, protandry and herkogamy were more frequent than dichogamy, protogyny and no herkogamy, respectively. Xenogamous species tend to be woody and grow in undisturbed areas, while partially xenogamous species were mainly herbs occurring in disturbed areas. The majority of species were partially self-incompatible. High levels of outbreeding strategies tended to occur mainly in woody K-strategy species from undisturbed areas, mixed breeding strategies occurred in disturbed areas and overall community, and inbreeding strategies were associated with mostly herbaceous r-strategy primarily in disturbed areas.