The Functional Significance of Poricidal Anthers and Buzz Pollination: Controlled Pollen Removal From Dodecatheon

Abstract

1. Given the diminishing returns associated with animal pollination, floral mechanisms that restrict pollen removal by individual pollinators and encourage transport on many pollinators generally promote a plant's cumulative success in pollen dispersal. Effective mechanisms for dispensing pollen should allow facultative adjustment of removal in response to the prevailing frequency of visits to a plant. 2. We investigated whether the poricidal anthers of Dodecatheon conjugens, a buzz-pollinated species, function as dispensing mechanisms by (a) comparing pollen removal in response to buzz frequencies that pollen-collecting bumble-bees (Bombus spp.) produce (≤400 Hz) with removal stimulated by higher frequencies and (b) comparing removal from flowers that waited different periods of time for their first visit. 3. Mechanical vibration of D. conjugens flowers for 1s at frequencies ≤400 Hz removed an average of 9.7% of available pollen, compared to 23.4% for 450-1000 Hz vibrations (all frequencies involved similar input energy). Buzzing by bees and mechanical vibration removed more pollen from older virgin flowers. 4. These results imply that the poricidal anthers of Dodecatheon flowers are `tuned' higher than the buzz frequencies used by their pollen-collecting pollinators, so that they effectively restrict pollen removal, while also allowing increased removal when visits occur rarely. Previously published results from other buzz-pollinated species indicate that poricidal anthers generally function as dispensing mechanisms. 5. Poricidal anthers probably enabled convergent evolution of the solanoid flower, which localizes pollinator-flower contact so as to reduce pollen loss during transport.