The functional implications of active and passive pollination in dioeciousfigs

Fig-pollinating wasps lay their eggs in fig flowers. Some species of fig-po llinating wasps are active pollinators, while others passively transfer pol len. In dioecious fig species, the ovules of male figs produce wasps but no seeds. By observations and experiments on four dioecious Ficus species we show that (i) passive pollinators distribute pollen haphazardly within figs , but fertilization of female flowers in male figs is inhibited. Consequent ly, wasp larvae will develop in nonfertilized ovules: they cannot benefit f rom pollination; (ii) active pollinators efficiently fertilize flowers in w hich they oviposit. Lack of pollination increases larval mortality. Hence, fig pollinators are not obligate seed eaters but ovule gallers. Active poll ination has probably evolved as a way to improve progeny nourishment. Comparison of pollination and oviposition process in male and female figs, suggests that stigma shape and function have coevolved with pollination beh aviour, in relation to constraints linked with dioecy.