title: A pollinators' eye view of a shelter mimicry system.
abstract: OBJECTIVE
  '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).
  
  
  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.
authors.affiliation: Evolutionary Biology & Ecology, Free University of Brussels/Université Libre de Bruxelles, Av. F.D. Roosevelt 50, Brussels, Belgium. nicolas.vereecken@ulb.ac.be
authors.forename: Nicolas J
authors.initials: NJ
authors.lastname: Vereecken
authors.forename: Achik
authors.initials: A
authors.lastname: Dorchin
authors.forename: Amots
authors.initials: A
authors.lastname: Dafni
authors.forename: Susann
authors.initials: S
authors.lastname: Hötling
authors.forename: Stefan
authors.initials: S
authors.lastname: Schulz
authors.forename: Stella
authors.initials: S
authors.lastname: Watts
mesh_terms: D000220:Adaptation, Biological; D000818:Animals; D001516:Bees / Q000502:physiology*; D005075:Biological Evolution; D003116:Color; D035264:Flowers / Q000033:anatomy & histology*; D031323:Iris Plant / Q000033:anatomy & histology*; D008297:Male; D009812:Odorants; D010641:Phenotype; D054817:Pollination
keywords: Iris atropurpurea; Oncocyclus; Shelter mimicry; floral colours; floral evolution; floral scents; pollinator preferences