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INSIDE THE TRAP OF A YELLOW LADY'S SLIPPER ORCHID (CYPRIPEDIUM PARVIFLORUM VAR. PUBESCENS): THE EFFECTS OF 'LIGHT WINDOWS' AND FLOWER ORIENTATION ON THE BEHAVIOR OF A NATIVE BEE (ANDRENA MACRA)

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Author: Forrester, Nicole Jacqueline
Advisor: Case, Martha
Committee Members: Fashing, Norman; King, Barbara; Leu, Matthias
Issued Date: 5/14/2011
Subjects: Orchid
Light windows
Geotaxis
Phototaxis
Cypripedium
Andrena macra
Pollination
Lady's slipper
URI: http://hdl.handle.net/10288/13732
Description: Darwin's (1862) famous work on the mechanisms and diversity of pollination in the Orchidaceae highlights the fascinating nature of plant-pollinator interactions in a variety of orchid genera. One particularly interesting aspect of orchid pollination is that about one third of orchid species is deceptive and offers no reward to pollinators. Despite the interest in orchid pollination, relatively few studies have observed pollination in non-rewarding orchids and documented successful pollinator species. This has led to the persistence of various untested hypotheses concerning some pollination mechanisms. For example, the light windows hypothesis posits that the thin tissue beneath the exit holes of the labellum serve as light windows to guide pollinators to the correct escape route out of the labellum. However, many insects are also influenced by geotaxis, and the labellum might also capitalize on innate negative geotactic behavior of visiting insects by providing a vertical escape passageway in the labellum. Despite profuse discussion of the alleged function of light windows in the literature, this is the first study to rigorously test the light windows hypothesis and determine the influence of flower orientation on insect behavior. In order to test these ideas, Andrena macra bees were introduced into experimentally manipulated labella of Cypripedium parviflorum var. pubescens plants in the field as well as choice chambers in the laboratory with the following goals in mind: (1) to determine if light windows are required for pollinators to orient to the correct escape route and exit the plant, (2) to understand the influence of labellum orientation on pollinator behaviors, and (3) to correlate field observations with phototactic and geotactic responses in the laboratory. There were no significant differences observed in bee behaviors for plants with light windows covered compared to control plants, and the bees still oriented to the proper exit even when additional light from the exit holes was blocked. However, there were significant differences in bee behavior when the labellum was abnormally oriented, with bees tending to attempt an incorrect exit much more often when flowers were tilted 90 ° backwards or sideways. For Andrena macra, light windows in C. parviflorum were not required for their proper orientation to the correct escape route or escape from the plant. Finally, laboratory data were consistent with field data, suggesting that gravity, not light, more strongly influences correct exiting behaviors.
Degree: Bachelors of Arts in Biology


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