Deceptive pollination in two subspecies of Disa spathulata (Orchidaceae) differing in morphology and floral fragrance |
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Authors: | S.D. Johnson K.E. Steiner R. Kaiser |
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Affiliation: | (1) School of Botany and Zoology, University of KwaZulu-Natal, P. Bag X01, Scottsville, Pietermaritzburg, 3209, South Africa;(2) California Academy of Sciences, 875 Howard St., San Francisco, CA 94103, USA;(3) Givaudan Schweiz AG, Fragrance Research, 8600 Dubendorf, Switzerland |
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Abstract: | The non-rewarding flowers of Disa spathulata (L.f) Sw. have a highly elongated scent-producing lip that varies in size and form between the two subspecies of this orchid. We investigated whether this unusual morphology is associated with the evolution of a specialized scent-based pollination system. Field observations carried out in South Africa showed that flowers of D. spathulata are pollinated solely by bees belonging to the genus Tetraloniella (Anthophoridae). Flowers of D. spathulata subsp. spathulata were visited by Tetraloniella brevikeraia, while flowers of D. spathulata subsp. tripartita (Lindl.). H. P. Linder were visited by Tetraloniella junodi. The floral fragrance of D. spathulata is emitted by the lip blade and differs markedly between the two subspecies (only 24 [42.1] of the 57 compounds identified were shared). Fragrance of D. spathulata subsp spathulata is dominated by the fatty acid derivatives decyl actetate, octanol, and decanol, while that of D. spathulata subsp. tripartita is dominated by the terpenoids (E) - ocimene, caryophyllene, and (E) nerolidol. Both male and female Tetraloniella bees were strongly attracted to cut flowers of D. spathulata subsp spathulata, even at sites where the orchid does not naturally occur. Bees visit the orchids repeatedly despite the lack of rewards in their flowers. Sexual deception in D. spathulata can be excluded by the attraction of both male and female bees, and yet the manner in which bees are attracted seems too intense and species-specific to be characterized as food-deception. This implies the existence in D. spathulata of a system of scent-based deception of insects that has not been described previously in plants. |
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Keywords: | Bee-pollination Ecotypes Floral evolution Floral scent GCMS Mimicry Orchid pollination Speciation |
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