A pollinators' eye view of a shelter mimicry system

Nicolas J. Vereecken, Achik Dorchin, Amots Dafni, Susann Hötling, Stefan Schulz, Stella Watts

Research output: Contribution to journalArticlepeer-review


Background and Aims 'Human-red' flowers are traditionally considered to be rather unpopular with bees, yet some allogamous species in the section Oncocyclus (genus Iris, Iridaceae) have evolved specialized interactions with their pollinators, a narrow taxonomic range of male solitary bees. The dark-red, tubular flowers of these irises are nectarless but provide protective shelters (i.e. a non-nutritive form of reward) primarily to male solitary bees (Apidae, Eucerini) that pollinate the flowers while looking for a shelter. An earlier study on orchids suggested that species pollinated predominantly by male solitary bees produce significantly larger amounts and larger numbers of different n-alkenes (unsaturated cuticular hydrocarbons). Whether or not this also applies to the Oncocyclus irises and whether pollinators are attracted by specific colours or scents of these flowers is unknown. Methods Using Iris atropurpurea, recording of pollinator preferences for shelters with different spatial parameters was combined with analyses of floral colours (by spectrophotometry) and scents (by gas chromatography-mass spectrometry) to test the hypotheses that (a) pollinators significantly prefer floral tunnels facing the rising sun (floral heat-reward hypothesis), and that (b) flowers pollinated predominantly by male solitary bees produce significantly larger amounts and larger numbers of unsaturated cuticular hydrocarbons (n-alkenes) in their floral scent (preadaptation to sexual-deception hypothesis). Key Results Male bees do not significantly prefer shelters facing the rising sun or with the presence of high absolute/relative amounts and numbers of n-alkenes in the floral scent. Conclusions The results suggest that the flowers of I. atropurpurea probably evolved by pollinator-mediated selection acting primarily on floral colours to mimic large achromatic ('bee-black') protective shelters used preferentially by male solitary bees, and that pollinator visits are presumably not the result of an odour-based sexual stimulation or motivated by an increased morning floral heat reward in tunnels facing the rising sun.

Original languageEnglish
Pages (from-to)1155-1165
Number of pages11
JournalAnnals of Botany
Issue number6
StatePublished - Jun 2013

Bibliographical note

Funding Information:
This work was financially supported by the Belgian FRS-FNRS (Fonds National pour la Recherche Scientifique) through a post-doctoral grant (‘Chargé de Recherches’) and several travel grants (2008–2012) to N. J. Vereecken. We are grateful to J. Ollerton, P. G. Kevan, S. P. M. Roberts, M. Streinzer, J. Spaethe, Y. Sapir and S. Risch for fruitful discussions during the preparation of this study, to C. Agostinelli, J. H. McDonald and G. Elvers for statistical advice, and to three anonymous referees for their helpful comments on an earlier version of the manuscript. We thank B. Segal and N. Bensoussan for field assistance. The experiments comply with the current laws of the country in which the experiments were performed.


  • Iris atropurpurea
  • Oncocyclus
  • Shelter mimicry
  • floral colours
  • floral evolution
  • floral scents
  • pollinator preferences

ASJC Scopus subject areas

  • Plant Science


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