MATING COST OF LARGE FLORAL DISPLAYS IN HERMAPHRODITE PLANTS

HERMAPHRODITISM comprises outcrossing whenever the proximity of male a nd female organs allows self-fertilization(1) and interference between sexual functions(2). Many floral traits of animal-pollinated angiospe rms encourage cross-fertilization(3), as recognized by Darwin(4-6); ho wever, these characteristics may also allow pollination between flower s on the same individual (geitonogamous self-pollination)(7,8). Simult aneous display of many flowers exemplifies this conflict. Although lar ge floral displays promote outcrossing through enhanced pollinator att raction(9), they could be costly in terms of lost mating opportunities (10,11) if geitonogamy decreased outcrossed siring success by reducing pollen transfer between plants (pollen discounting(12)). We report he re that, after manipulating the flower number of bee-pollinated Eichho rnia paniculata plants, we observed the predicted higher selfing and l ower outcrossed siring success for larger inflorescences. Given the re duced fitness resulting when pollen receipt by one flower interferes w ith pollen export by another, we propose broadening traditional interp retations of floral design and display to recognize their roles in red ucing geitonogamous pollen discounting.