Journal Article

A key role for floral scent in a wasp-pollination system in <i>Eucomis</i> (Hyacinthaceae)

A. Shuttleworth and S. D. Johnson

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 103, issue 5, pages 715-725
Published in print March 2009 | ISSN: 0305-7364
Published online December 2008 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcn261
A key role for floral scent in a wasp-pollination system in Eucomis (Hyacinthaceae)

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

Floral scent may play a key role as a selective attractant in plants with specialized pollination systems, particularly in cases where floral morphology does not function as a filter of flower visitors. The pollination systems of two African Eucomis species (E. autumnalis and E. comosa) were investigated and a test was made of the importance of scent and visual cues as floral attractants.

Methods and Key Results

Visitor observations showed that E. autumnalis and E. comosa are visited primarily by pompilid wasps belonging to the genus Hemipepsis. These wasps carry considerably more Eucomis pollen and are more active on flowers than other visiting insects. Furthermore, experiments involving virgin flowers showed that these insects are capable of depositing pollen on the stigmas of E. autumnalis, and, in the case of E. comosa, pollen deposited during a single visit is sufficient to result in seed set. Experimental hand-pollinations showed that both species are genetically self-incompatible and thus reliant on pollinators for seed set. Choice experiments conducted in the field and laboratory with E. autumnalis demonstrated that pompilid wasps are attracted to flowers primarily by scent and not visual cues. Measurement of spectral reflectance by flower petals showed that flowers are cryptically coloured and are similar to the background vegetation. Analysis of headspace scent samples using coupled gas chromatography–mass spectrometry revealed that E. autumnalis and E. comosa scents are dominated by aromatic and monoterpene compounds. One hundred and four volatile compounds were identified in the floral scent of E. autumnalis and 83 in the floral scent of E. comosa, of which 57 were common to the scents of both species.

Conclusions

This study showed that E. autumnalis and E. comosa are specialized for pollination by pompilid wasps in the genus Hemipepsis and achieve specialization through cryptic colouring and the use of scent as a selective floral attractant.

Keywords: Eucomis; Pompilidae; wasp pollination; breeding system; pollination syndrome; pollinator shift; floral volatile; floral filter

Journal Article.  7581 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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