Two phylogenetically distinct species of sexually deceptive orchids mimic the sex pheromone of their single common pollinator, the cuckoo bumblebee Bombus vestalis |
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Authors: | Julia G?gler Robert Twele Wittko Francke Manfred Ayasse |
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Institution: | (1) Institute for Experimental Ecology, University of Ulm, Albert-Einstein-Allee 11, 89069 Ulm, Germany;(2) Institute of Organic Chemistry, University of Hamburg, Martin-Luther-King Platz 6, 20146 Hamburg, Germany; |
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Abstract: | Sexually deceptive orchids of the genus Ophrys attract male insects for pollination. Pollinator attraction is achieved by mimicking sex pheromones of virgin females of
their pollinators, mostly bee species. In earlier investigations, we showed that the phylogenetically distinct Ophrys species O.
chestermanii and O. normanii on Sardinia attract their pollinator, males of the cuckoo bumblebee B. vestalis, with the same bouquets of relatively polar volatile compounds. In this investigation, we studied the sex pheromone of virgin
females of B. vestalis with the aim of identifying male-attracting compounds and of comparing them with labellum extracts of the two orchids, which
were found to release male-attracting compounds in earlier investigations (G?gler et al. 2009). In bioassays, shock-frozen females, cuticle extracts and polar fractions of cuticle extracts of virgin females stimulated
mating behaviour in the males. Using gas chromatography coupled with electroantennography (GC-EAD) and gas chromatography
coupled with mass spectrometry (GC-MS), we detected in polar fractions of cuticle extracts of B. vestalis females the same electrophysiologically active compounds as in labellum extracts of both orchid species, including aldehydes,
esters, fatty acids and alcohols. Since statistical comparisons of the relative proportions of esters showed strong similarities
between virgin females and orchids, our results support the hypotheses that this highly specialized Ophrys–pollinator relationship represents another case of chemical mimicry and that esters play a key role in male attraction. |
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