Effects of Pollen Vector and Plant Geometry on Floral Sex Ratio in Monoecious Plants

Abstract

-Size-related patterns of floral sex allocation were examined in 14 anemophilous and eight entomophilous monoecious plants. Among the anemophilous species, eight increased male floral allocation and six increased female floral allocation with increased plant size. An increase in female floral allocation with increased plant size occurred in all eight entomophilous monoecious species examined. Pollination vector has a significant effect on size-related floral sex ratio patterns. We present a heuristic model that considers pollen dispersal of anemophilous monoecious plants as a function of plant geometry. The surface area to volume ratio of plants approximating geometric extremes (cylindrical or spherical forms) should affect pollen dispersal and floral sex ratio due to aerodynamic effects on the whole plant. Plants approximating cylinders should increase male floral allocation with increasing height. Plants that approximate a more spherical form should increase in female floral allocation with increasing size. All entomophilous plants conformed to a resource limitation model; however, anemophilous plants increased in either male or female floral allocation with increased size. Results for 13 anemophilous species support the predictions of our geometric model. One species does not approximate an extreme geometry and does not appear to conform to the geometrical model's predictions.