, Volume 234, Issue 1-4, pp 111-119

Do changes in floral odor cause speciation in sexually deceptive orchids?

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 We investigated differences in floral odor between two sympatric, closely related sexually deceptive orchid species, Ophrys fusca and O. bilunulata, which are specifically pollinated by Andrena nigroaenea and A. flavipes, respectively. We identified biologically active compounds by gas chromatography with electroantennographic detection using antennae of the pollinator bees. Alkanes, alkenes, aldehydes, and farnesyl hexanoate released electroantennographic reactions. The relative amounts of alkanes were mostly the same between the two orchid species, whereas the relative amounts of most alkenes were significantly different. On the grounds of these findings and behavioral experiments conducted in earlier studies, we suggest that the difference in relative amounts of alkenes is responsible for the selective attraction of pollinators in the two orchids. Speciation in this group of Ophrys orchids may be brought about by changes in pattern of alkenes, which lead to attraction of a different pollinator species and therefore reproductive isolation.

Received November 22, 2001; accepted February 21, 2002 Published online: November 7, 2002
Addresses of the authors: Florian P. Schiestl* and Manfred Ayasse, Department of Evolutionary Biology, Institute of Zoology, University of Vienna, Althanstrasse 14, A-1090 Vienna. *Present address: Geobotanical Institute ETH, Zollikerstrasse 107, CH-8008 Zürich. (e-mail: schiestl@geobot.umnw.ethz.ch)