COS 130-2 - How do orchids talk to bees?

Friday, August 12, 2011: 8:20 AM
9C, Austin Convention Center
Mani Shrestha, School of Biological Sciences, Clayton Campus, Monash University, Victoria-3800, Australia, Martin Burd, School of Biological Sciences, Monash University, Melbourne, Australia and Adrian Dyer, School of Media and Communication, RMIT University, Vic, 3001, Australia

Many hymenopteran floral visitors exhibit flower constancy because they discriminate among floral colors, and many angiosperm species, in turn, tend to signal pollinators using the colors that hymenoptera discriminate best. What colors do deceptive, non-rewarding angiosperms use, and are they similar or different to colors of rewarding species? To test this question we measured the spectral reflectance functions of flowers from 63 rewarding and non-rewarding orchid species that occur together in a natural community in eucalyptus woodland in south-eastern Australia. We determined the inflection points where reflectance changes rapidly and plotted the frequency of these points along the light spectrum.


We found that both rewarding and non-rewarding orchid species tend to use colors with sharp reflectance changes at 400 and 500 nm wavelength where colour stimuli are best discriminated by trichromatic pollinators with UV-Blue-Green sensitive photoreceptors. Next we plotted the reflectance curves in an ecologically relevant model of bee color vision, and tested if orchid flowers are grouped in colour space based on phylogeny. Surprisingly, there was no congruence between phylogeny and distribution of reflectance curves in a colour space, suggesting orchid can rapidly evolve a wide range of pigmentations for advertising signals to pollinators. Both nectar reward levels and floral colors appear to have been highly labile traits in the evolution of the Orchidaceae

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