title: Chemical and morphological filters in a specialized floral mimicry system.
abstract: Many plant species attract insect pollinators through chemical mimicry of their oviposition sites, often detaining them in a trap chamber that ensures pollen transfer. These plant mimics are considered to be unspecialized at the pollinator species level, yet field observations of a mycoheterotrophic rainforest orchid (Gastrodia similis), which emits an odour reminiscent of rotting fruit, indicate that it is pollinated by a single drosophilid fly species (Scaptodrosophila bangi). We investigated the roles of floral volatiles and the dimensions of the trap chamber in enforcing this specialization, using gas chromatography-mass spectrometry analyses, bioassays and scanning electron microscopy. We showed that G. similis flowers predominantly emit three fatty-acid esters (ethyl acetate, ethyl isobutyrate and methyl isobutyrate) that were shown in experiments to attract only Scaptodrosophila flies. We additionally showed that the trap chamber, which flies enter into via a touch-sensitive 'trapdoor', closely matches the body size of the pollinator species S. bangi and plays a key role in pollen transfer. Our study demonstrates that specialization in oviposition site mimicry is due primarily to volatile chemistry and is reflected in the dimensions of the trapping apparatus. It also indicates that mycoheterotrophic plants can be specialized both on mycorrhizal fungi and insect pollinators.
authors.affiliation: School of Life Sciences, University of KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville, 3209, South Africa.
authors.forename: Florent
authors.initials: F
authors.lastname: Martos
authors.affiliation: Evolution, Génomes et Spéciation, UPR 9034, CNRS, Avenue de la Terrasse, Bâtiment 13, BP1, 91198, Gif-sur-Yvette Cedex, France.
authors.forename: Marie-Louise
authors.initials: ML
authors.lastname: Cariou
authors.affiliation: Peuplements Végétaux et Bio agresseurs en Milieu Tropical, UMR C53, Université de La Réunion, Avenue René Cassin, 97715, Saint Denis Cedex, La Réunion.
authors.forename: Thierry
authors.initials: T
authors.lastname: Pailler
authors.affiliation: Peuplements Végétaux et Bio agresseurs en Milieu Tropical, UMR C53, Université de La Réunion, Avenue René Cassin, 97715, Saint Denis Cedex, La Réunion.
authors.forename: Jacques
authors.initials: J
authors.lastname: Fournel
authors.affiliation: School of Life Sciences, University of KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville, 3209, South Africa.
authors.forename: Benny
authors.initials: B
authors.lastname: Bytebier
authors.affiliation: School of Life Sciences, University of KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville, 3209, South Africa.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Johnson
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D004330:Drosophila / Q000502:physiology; D035264:Flowers / Q000033:anatomy & histology* / Q000737:chemistry*; D029595:Orchidaceae / Q000502:physiology*; D054817:Pollination; D055549:Volatile Organic Compounds / Q000032:analysis
chemical_list: D055549:Volatile Organic Compounds
keywords: Gastrodia; Scaptodrosophila; floral signalling; mycoheterotrophic plants; pollinator specialization; rotting fruit/yeast mimicry; semiochemicals; touch-sensitive organ