Plant Biology Readings

Biology 59: Plant Biology

George M. Diggs, Jr.
Department of Biology and Center for Environmental Studies
Austin College, Sherman, Texas
& Research Associate, Botanical Research Institute of Texas (BRIT), Fort Worth

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Vibrator or Buzz Pollination
From Diggs et al., Illustrated Flora of East Texas, Volume 2 (in prep.)

A number of species exhibit the “vibrator,” “vibrational,” or “buzz” pollination syndrome, which has evolved as an effective mechanism for transferring pollen via pollen-collecting insects such as bumblebees---while pollen is the reward utilized by the bee, at least some pollen is inadvertently transferred to other flowers). The bees shake the anthers by vibrating/shivering their thoracic flight muscles at a certain frequency; this audible “buzz” sets up a resonance in the anthers or the space they enclose and the otherwise inaccessible pollen is released from the terminal pores of the anthers and collected by the insect. The porate anthers serve as an effective dispensing mechanism, which release some pollen, but not so much that all available pollen is given to a single insect. This limitation maximizes the chance of successful pollen dispersal. There are several hypotheses for the turned back (reflexed) corollas and exposed anther-cone typical of “vibrator”-type flowers. This “solanoid” flower structure (named after the genus Solanum which has similar flowers) may be an adaptation to minimize either dampening of vibration resonance or hindrance of pollinator access to the anthers (e.g., corolla out of the way), it may be an adaptation related to microclimate in the flower (e.g., anthers not enclosed with a relatively humid chamber formed by the corolla---thus keeping the pollen in a dry powdery condition so that it is easily dispersed), or the exposed, often colorful, frequently dark anthers may function as a visual signal of the available pollen reward or permit radiative warming and thus drier, more powdery pollen. In addition, the flowers hang down, causing the bee to curl its body under the anther-cone in order to catch the pollen as it is expelled. It has been proposed that this results in at least some of the pollen being deposited underneath the bee’s body in areas that are poorly groomed---thus insuring some effective pollen transfer to another flower (Macior 1964; Buchmann 1983; Erickson & Buchmann 1983; Barth 1985; Corbet et al. 1988; Harder & Barclay 1994; King & Buchmann 1996; Proctor et al. 1996).