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Morning floral heat as a reward to the pollinators of the Oncocyclus irises

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Relationships between flowering plants and their pollinators are usually affected by the amount of reward, mainly pollen or nectar, offered to pollinators by flowers, with these amounts usually positively correlated with floral display. The large Oncocyclus iris flowers, despite being the largest flowers in the East Mediterranean flora, are nectarless and have hidden pollen. No pollinators visit the flowers during daytime, and these flowers are pollinated only by night-sheltering solitary male bees. These iris flowers are partially or fully dark-colored, suggesting that they gather heat by absorbing solar radiation. Here we test the hypothesis that the dark-colored flowers of the Oncocyclus irises offer heat reward to their male solitary bee pollinators. Floral temperature was higher by 2.5°C than ambient air after sunrise. Solitary male bees emerged earlier after sheltering in Oncocyclus flowers than from other experimental shelter types. Pollination tunnels facing east towards the rising sun hosted more male bees than other aspects. We suggest that floral heat reward can explain the evolution of dark floral colors in Oncocyclus irises, mediated by the pollinators’ behavior.

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We thank R. Kashi, O. Spiegel and nature-guides of Keshet field-school for their help in field work. B. Gross, N. Kane, P. Kevan, L. Kurz, J. Ollerton, J. Shykoff, and an anonymous reviewer helped to improve early versions of the manuscript. The research was supported by a grant from the Deutsche Forschungs Gemeinschaft (Co-254/1-1) to A.S., and a grant from the American Iris Society Foundation to Y.S.

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Correspondence to Yuval Sapir.

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Communicated by Jacqui Shykoff

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Sapir, Y., Shmida, A. & Ne’eman, G. Morning floral heat as a reward to the pollinators of the Oncocyclus irises. Oecologia 147, 53–59 (2006). https://doi.org/10.1007/s00442-005-0246-6

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  • Bee behavior
  • Iridaceae
  • Nectar-less flowers
  • Night shelter
  • Solitary male bees
  • Thermal reward