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Keywords:

  • deceptive orchids;
  • female fitness;
  • floral evolution;
  • natural selection;
  • plant–animal interactions;
  • pollen limitation;
  • pollinator-mediated selection;
  • selection gradients

Summary

  • Nonrewarding animal-pollinated plants commonly experience severe pollen limitation, which should result in strong selection on traits affecting the success of pollination. However, the importance of pollinators as selective agents on floral traits in deceptive species has not been quantified experimentally.
  • Here, we quantified pollinator-mediated selection (Δβpoll) on floral morphology and start of flowering in the deceptive orchid Dactylorhiza lapponica by subtracting estimates of selection gradients for plants receiving supplemental hand-pollination from estimates obtained for open-pollinated control plants.
  • There was directional selection for taller plants with more flowers and longer spurs, but no statistically significant selection on corolla size or flowering start. Pollinator-mediated selection accounted for all observed selection on spur length (Δβpoll = 0.32), 76% of the selection on plant height (Δβpoll = 0.19) and 42% of the selection on number of flowers (Δβpoll = 0.30). Sixteen per cent of developing fruits were consumed by insect herbivores, but fruit herbivory had only minor effects on the strength of pollinator-mediated selection.
  • Our results demonstrate that pollinators mediate selection on floral traits likely to affect both pollinator attraction and pollination efficiency, and are consistent with the hypothesis that deceptive species experience strong selection for increased display and mechanical fit between flower and pollinator.