Evolution of Flower Allometry and Its Significance for Pollination Success in the Deceptive Orchid Pogonia japonica

Pollinator-mediated selection in the deceptive orchid Pogonia japonica was studied by comparing the amount of variation in and the relative size relationships between the petals, sepals, and gynostemium. The gynostemium length had a significantly lower slope in log-log regression on the indicator of the flower size for its length than did the petals or sepals. This indicates that pollinator-mediated selection may lead to low phenotypic variation of gynostemium length. Pollinia removal by pollinators and pollinia-pollinated stigma were rarely observed in the field. Flowers whose pollinia were removed had a significantly smaller gynostemium than flowers with intact pollinia. There was no significant difference in the sizes of floral organs between pollinated and unpollinated flowers. These results indicate that the size of the gynostemium in Pogonia has evolved to increase male reproductive success.