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Tropical Biology Section

Blanco, Mario A. [1], Barboza, Gabriel [2].

Pseudocopulatory pollination in Lepanthes (Orchidaceae: Pleurothallidinae) by fungus gnats.

Lepanthes is one of the largest angiosperm genera (>900 species). Their non-rewarding, tiny, and colorful flowers are structurally complex. Their pollination mechanism has long remained unknown, and has been subject of ample speculation; the function of the minuscule labellum appendix was especially puzzling. We observed, photographed, and collected floral visitors in L. glicensteinii in Monteverde, Costa Rica. We also observed occasional visits to flowers of L. helleri, L. stenorhyncha, and L. turialvae. Sexually aroused males of the fungus gnat Bradysia floribunda (Diptera: Sciaridae) were the only visitors and pollinators of L. glicensteinii. These insects always approach the flowers from downwind, as if following a scent plume. Upon finding a flower, the gnat curls his abdomen under the blades of the labellum and grabs the appendix with his genitalic claspers, then dismounts the flower and turns around to face away from it. The pollinarium becomes attached to his abdomen during this pivoting maneuver. The gnats appear to deposit a spermatophore in the flower (ejaculation). This series of events closely follows the male sciarid's normal mating sequence. Pollinia are deposited on the stigma during a subsequent flower visit. The visitors of L. helleri, L. stenorhyncha and L. turialvae are different species of fungus gnats that display a similar behavior. This special mode of sexual deception, where genitalic coupling of the insect with the flower is a necessary step for pollen transfer, is termed genitalic pseudocopulatory pollination, and is otherwise known only in the Australian orchid genus Cryptostylis. This is the first documented case of sexually deceptive pollination in the large Neotropical orchid subtribe Pleurothallidinae (>4000 species). Since most species of Lepanthes share the same unusual flower structure, we predict that pollination by sexual deception is prevalent in the genus.


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1 - University of Florida, Department of Botany, 220 Bartram Hall, P.O. Box 118526, Gainesville, Florida, 32611-8526, USA
2 - Monteverde Orchid Garden, Monteverde, Puntarenas, 83-5655, Costa Rica

Keywords:
pollination
Lepanthes
Orchidaceae
sexual mimicry
fungus gnats.

Presentation Type: Oral Paper
Session: 8-1
Location: 410/Hilton
Date: Monday, August 15th, 2005
Time: 10:15 AM
Abstract ID:404


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