COMPONENTS OF REPRODUCTIVE SUCCESS IN TWO DIOECIOUS FIG SPECIES,FICUS EXASPERATAANDFICUS HISPIDA

Abstract

We studied components of reproductive success in two dioecious fig species, Ficus exasperata and F. hispida, at a deciduous and an evergreen site in south India, over a two-year period. Unlike monoecious figs, which produce a mixture of wasps, seeds, and pollen in every fruit, dioecious fig species have hermaphrodite (functionally male) trees, which produce wasps and pollen only, and female trees, which produce seeds only. Di- oecious fig species are free of the seed-wasp trade-off involved within each monoecious fig fruit; wasp and seed production in dioecious species reflect selective pressures acting on each sex to maximize offspring production. We studied specific predictions of the reproductive behavior of dioecious fig species, predictions that were made based on studies of monoecious figs. Pollinator (and associated parasitic wasp) arrivals at trees bearing receptive inflores- cences were closely linked to the seasonal variation in receptive fig numbers. More wasps arrived at female trees of F. exasperata than at trees, apparently because of syn- chronized wasp release by male trees during the time of synchronous female tree receptivity. Wasp numbers arriving at male and female trees of F. hispida did not differ significantly, apparently because inflorescence production on male and female trees was more evenly spread over time. Female inflorescences had more pollinators than male inflorescences in F. hispida; female and male inflorescences had approximately equal numbers of pollinators in F. exasperata. Hand-pollination experiments introducing one, three, or eight pollinators into figs of F. hispida showed that foundress number was a significant predictor of resultant wasp or seed number. In both fig species, female inflorescences initiated more flowers than male inflorescences, and produced more seeds than male inflorescences produced wasps. Female fruits were not larger than male fruits at maturity in either fig species. Only in F. exasperata were male fruits significantly smaller in the dry than in the wet site. Both species had a relatively high average level of pollination (>70%). The mean percentage of fruit matured was 56% in F. hispida, and a surprisingly high 78% in F. exasperata. Both fig species exhibited strong sex differences in foundress numbers, numbers of flowers initiated, and numbers of wasps or seeds matured, suggesting strong selection on components of reproductive success within each sex after dioecy evolved. Our quantitative analyses elucidate how some of the many factors in plant-pollinator relationships affect plant reproductive success in the fig-wasp mutualism.