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New Phytol. 2010 Oct;188(2):437-50. doi: 10.1111/j.1469-8137.2010.03308.x. Epub 2010 Jun 7.

Pollinator specificity, floral odour chemistry and the phylogeny of Australian sexually deceptive Chiloglottis orchids: implications for pollinator-driven speciation.

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1
Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, ACT, Australia. rod.peakall@anu.edu.au

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.

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