Olfactory versus visual cues in a floral mimicry system |
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Authors: | B A Roy R A Raguso |
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Institution: | (1) The Center For Population Biology, University of California, Davis, CA 95616, USA, US;(2) Department of Biology, University of Michigan, Ann Arbor, MI 48109-1048, USA, US |
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Abstract: | We used arrays of artificial flowers with and without fragrance to determine the importance of olfactory and visual cues
in attracting insects to a floral mimic. The mimic is a fungus, Puccinia
monoica Arth., which causes its crucifer hosts (here, Arabis
drummondii Gray) to form pseudoflowers that mimic co-occurring flowers such as the buttercup, Ranunculus
inamoenus Greene. Although pseudoflowers are visually similar to buttercups, their sweet fragrance is distinct. To determine whether
visitors to pseudoflowers were responding to fragrance we performed an experiment in which we removed the visual cues, but
allowed fragrance to still be perceived. In this experiment we found that pseudoflower fragrance can attract visitors by itself.
In other experiments we found that the relative importance of olfactory and visual cues depended on the species of visitor.
Halictid bees (Dialictus sp.) had a somewhat greater visual than olfactory response, whereas flies (muscids and anthomyiids) were more dependent on
olfactory cues. We also used bioassays to determine which of the many compounds present in the natural fragrance were responsible
for attraction. We found that halictid bees were equally attracted to pseudoflowers and to a blend containing phenylacetaldehyde,
2-phenylethanol, benzaldehyde and methylbenzoate in the same relative concentrations as in pseudoflowers. Flies, on the other
hand, only responded to pseudoflower scent, indicating that we have not yet identified the compound(s) present in pseudoflowers
that are attracting them. The ability of insects to differentiate pseudoflowers from true flowers by their fragrance may be
important in the evolution of the mimicry system. Different fragrances may facilitate proper transfer of both fungal spermatia
and pollen, and thus make it possible for the visual mimicry to evolve.
Received: 3 January 1996 / Accepted: 13 August 1996 |
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Keywords: | Halictid bees Diptera Floral fragrance Pollination ecology Rust fungi |
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