Specific ant-pollination in an alpine orchid and the role of floral scent in attracting pollinating ants

Abstract

Several studies have recently shown that floral scent can deter ants from flowers. However, when ants serve as reliable pollen vectors, for example in harsh, windy habitats, were flying insects are less active, plants should have evolved floral signals to attract them to the flowers. We tested this hypothesis in the alpine orchid, Chamorchis alpina. C. alpina was found to be predominantly ant pollinated, with some occasional pollination by ichneumonid wasps. In all three investigated populations, only two species of ants, Formica lemani and Leptothorax acervorum visited the flowers and removed pollinaria. These two pollinator ants were found to be among the most common ant species in all habitats, but other, non-pollinating ants were also frequently found, suggesting a factor that mediates specific pollination. Floral morphology was found to be compatible with at least one of the common non-pollinator ants. Floral scent consistently comprised five terpenoid compounds, β-phellandrene, 1,8-cineole, linalool, α-terpineol, and β-caryophyllene. A synthetic blend of these five compounds emitting from rubber septa, was found to be attractive to one pollinator ant-species, F. lemani, in the field. The floral scent of C. alpina, through attracting only specific ants, may thus play a role in filtering floral visitors.

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Acknowledgments

We thank Reto Nyffeler and Merran Matthews for their initial help with finding populations of Chamorchis alpina. This study was financially supported by the Claratz Schenkung and the “Alpenblumenfonds” of the Swiss Botanical Society.

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Correspondence to Florian P. Schiestl.

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Schiestl, F.P., Glaser, F. Specific ant-pollination in an alpine orchid and the role of floral scent in attracting pollinating ants. Alp Botany 122, 1–9 (2012). https://doi.org/10.1007/s00035-011-0098-0

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Keywords

  • Floral VOC
  • Floral evolution
  • Floral filter
  • Orchidaceae
  • Formicidae