Selection by pollinators on the speciation of flowering plants

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A series of experiments to investigate the selective forces by pollinating insects on the flower size of Campanula (Campanulaceae) were carried out. I collected plants of Campanula from Honshu and the Izu Islands, and created an experimental population of Campanula with a large variation in flower size. First experiment was to present flowers with large variation to pollinators and to investigate their responces. The responces of pollinators (bumblebees, megachilid bees, halictid bees) was different from each other.Next experiment was to present flowers of male-phased flower with size variation and large female-phased flower to bumblebees and to investigate the male reproductive success in relation to male flower size. It was found that larger flowered-plants more sired than smaller flowered-ones.Third experiment was to investigate the amount and position of pollen grains to bumblebee body, using dried bumblebee specimens and fresh Campanula flowers. It was found that flower size determined the position of pollaen attached to bumblebees in which larger flowers were more appropriate to pollen deposition than smaller ones.It was suggested that flower size of Campanula is stabilized by the selection through morphological adaptation to bumblebee pollinators.