In multiple donor pollinations, pollen load size is expected to increase pollen competition and affect the paternity of seeds produced. In Passiflora incarnata, the number of pollen grains received on the stigmatic surfaces of individual flowers varies widely depending on style position. In this andromonoecious species, some flowers hold their styles erect where they are unlikely to come into contact with pollinators. Others reflex their styles to a position where contact with pollen-carrying pollinators is likely. Still others partially reflex their styles, but remain intermediate. In our field study in one Central Florida population, open-pollinated "male", intermediate, and hermaphroditic flowers received an average of 8.1 (s.d. = 11.9), 38.8 (s.d. = 38.0), and 385.7 (s.d. = 762.9) pollen grains, respectively. We found that pollen germination rates tend to be highest on hermaphroditic flowers (56.9%) and lowest on male flowers (30.9%), although this difference was not significant (F2,64 = 2.56, p = 0.08). Given that self-pollen germinates readily (but halts growth quickly), these differences in germination rates do not appear to be the result of differences among the amounts of self-pollen that may be received in the three style positions. Thus, in addition to the mechanical impediment to fruit production caused by style position, there appears to be a stigma-pollen interaction that affects the reproductive success of flowers expressing different genders. We are presently asking whether differences among male, intermediate, and hermaphroditic flowers may also affect pollen quality and hence the outcome of pollen competition.

Key words: andromonoecy, Passiflora incarnata, pollen competition, pollen load