Whereas in the rewarding A. coriophora stabilizing selection imposed by floral constancy of the pollinators may reduce scent variability, in the deceptive A. morio the emitted scent seems to be too weak to be detected by pollinators and thus its high variability may result from relaxed selection on this floral trait.

One third of all orchid species are deceptive and do not reward their pollinators. Such deceptive orchids are often characterised by unusually high variation in floral signals such as colour and scent. In this study, we investigated the scent composition of two Mediterranean food-deceptive orchids Orchis mascula, Orchis pauciflora, and their hybrid, O. x colemanii. Scent was collected IN SITU by headspace sorption and was subsequently analysed with gas chromatography and gas chromatography-mass spectrometry. We compared variation of odour compounds within and between populations as well as species. We identified 35 floral scent compounds, mainly monoterpenes, which were shared by both species. Both quantitative and qualitative variability within and among populations was high. Many individuals within species could be classified to different "odour-types". In spite of high qualitative and quantitative intra- and inter-population variability, the species were clearly differentiated in their scent bouquets, whereas most hybrid individuals emitted an intermediate scent.

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Orchids are extraordinary among plants because many species are pollinated through sexual duplicity by producing flowers that mimic female insects to lure unsuspecting males. Previous work showed that sexual deception by the orchid Chiloglottis trapeziformis can have a negative impact on its wasp pollinator Neozeleboria cryptoides. We report that female wasps may be capable of mitigating the cost of the orchids' deception. Although male wasps quickly habituated to areas planted with unrewarding flower decoys, we found that the effectiveness of the chemical cue used by the wingless females to attract males increases with increasing distance from an orchid patch. The apparent specif icity of the males' sitebased avoidance strategy means that females emerging in areas occupied by flowering orchids could, potentially, leave the orchid colony by walking to increase their attractiveness.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Chicago Press is collaborating with JSTOR to digitize, preserve and extend access to International Journal of Plant Sciences.The Australian orchid genus Caladenia is unusual in comprising species that have evolved different pollination syndromes, including food deception and sexual deception. In this study, we compare the scent emission of Caladenia longicauda Lindl. (food deceptive), Caladenia arenicola Hopper & A. P. Br. (sexually deceptive), and their putative F1 hybrids to investigate floral scent emission and its changes with the evolution of pollination syndromes. Floral scent was collected with headspace sorption. Odor compounds were identified with gas chromatography-mass spectrometry and quantitative differences analyzed with gas chromatography. Using floral volatiles, the two species could clearly be separated according to their scent profile, with hybrids occupying an intermediate position. The scent profile of the food-deceptive C. longicauda was dominated by benzenoids and isoprenoids, whereas in the sexually deceptive C. arenicola, benzenoids were reduced but fatty acid derivatives elevated. Caladenia longicauda emitted more scent than C. arenicola, both in absolute amount and in number of compounds. The patterns of floral odor emission are discussed in relation to the evolution of pollination syndromes.