Pollination Mode of Four Ficus species and Pollen Characteristics

Quantifying pollen is very important in the reproductive biology of plants. The pollen of Ficus species is quite tiny and abundant so that it is difficult to count pollen grains. So the anther-to-ovule ratio(A/O) is used to determine the pollination mode which are active and passive pollination. In this study, four monoecious Ficus species were selected to investigate their A/O ratios, and the pollination structures and behaviors of species-specific pollinating fig wasps were observed in order to determine the pollination mode. At the same time, the pollen sizes and numbers were measured, and studied the relationship between pollination mode and pollen characteristics.The results showed that the A/O ratios of Ficus religiosa,Ficus altissima and Ficus benjamina were less than 0.16, and the pollinating fig wasps had developed pollination structures and active behavior, which three Ficus species belonged to active pollination. However, Ficus curtipes had a high A/O ratio (0.85), and the coxal combs disappeared and pollen pockets degenerated, which was a characteristic of passive pollination. So F. curtipes was passive pollination. Pollen sizes of four Ficus species had significant variation. The numbers of pollen produced by a male flower were significant difference, and the figs had different numbers of male flowers so that the total numbers of pollen grains produced by a fig were significant difference among four Ficus species, which the range varied from 0.11 to 40 millions of grains per fig. The largest difference was 340 multiples between species. There was the trade-off relationship between the number of pollen and pollen sizes. Ficus species who was actively pollinated had few male flowers, produced large pollen grains and few pollen, while Ficus species belonging to passive pollination had more male flowers, produced small pollen grain and a lot of pollen. This suggests that the pollen characteristic and pollination structures of fig-pollinating wasps have evolved and matched with pollination mode in fig-fig wasp mutualism. The P/O ratios of four Ficus species were different, and the species that had a high P/O value did not represent to have a high A/O value. Using P/O ratio rather than A/O ratio can improve the research on pollination biology of Ficus species. Elzone Ⅱ 5390 Particle Size Analyzer efficiently and exactly counts pollen grains, and automatically outputs data. This provides the possibility for quantifying pollen of more Ficus species, and counting the pollen grains that carried by their species-specific pollinating fig wasps too. In this way, it will be advantage to discover the reproductive allocation on female and male function of Ficus species, and help us to understand the coevolutionary mechanism of fig-fig wasp mutualism.