title: Pollinator specificity, floral odour chemistry and the phylogeny of Australian sexually deceptive Chiloglottis orchids: implications for pollinator-driven speciation.
abstract: • Sexually deceptive orchids are predicted to represent a special case of plant speciation where strong reproductive isolation may be achieved by differences in floral scent. • In this study of Australian sexually deceptive Chiloglottis orchids, we performed choice experiments to test for wasp pollinator specificity in the field; identified the compounds involved in pollinator attraction by gas chromatography with electroantennographic detection (GC-EAD), gas chromatography with mass selective detection (GC-MS), chemical synthesis and behavioural bioassays; and mapped our chemical findings on to a phylogeny of the orchids. • Field experiments confirmed pollination is a highly specific interaction, but also revealed a pool of nonpollinating 'minor responder' wasps. Six novel compounds, all 2,5-dialkylcyclohexan-1,3-diones, called 'chiloglottones', were discovered to be involved in pollinator attraction. Bioassays confirmed that pollinator specificity has a strong chemical basis, with specificity among sympatric orchids maintained by either different single compounds or a variation in a blend of two compounds. The phylogenetic overlay confirmed that speciation is always associated with pollinator switching and usually underpinned by chemical change. • If the chemical differences that control reproductive isolation in Chiloglottis have a strong genetic basis, and given the confirmed pool of potential pollinators, we conclude that pollinator-driven speciation appears highly plausible in this system.
authors.affiliation: Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, ACT, Australia. rod.peakall@anu.edu.au
authors.forename: Rod
authors.initials: R
authors.lastname: Peakall
authors.forename: Daniel
authors.initials: D
authors.lastname: Ebert
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Poldy
authors.forename: Russell A
authors.initials: RA
authors.lastname: Barrow
authors.forename: Wittko
authors.initials: W
authors.lastname: Francke
authors.forename: Colin C
authors.initials: CC
authors.lastname: Bower
authors.forename: Florian P
authors.initials: FP
authors.lastname: Schiestl
mesh_terms: D000818:Animals; D001315:Australia; D001681:Biological Assay; D002755:Choice Behavior; D002849:Chromatography, Gas; D003512:Cyclohexanones / Q000032:analysis / Q000737:chemistry; D035264:Flowers / Q000737:chemistry*; D049810:Genetic Speciation; D008970:Molecular Weight; D009812:Odorants / Q000032:analysis*; D029595:Orchidaceae / Q000235:genetics*; D010802:Phylogeny; D054817:Pollination / Q000502:physiology*; D012098:Reproduction; D013045:Species Specificity; D014863:Wasps / Q000502:physiology*
chemical_list: D003512:Cyclohexanones