Floral Scent Emission and Pollination Syndromes: Evolutionary Changes from Food to Sexual Deception

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.