Flower signaling and orientation are key characteristics, which determine a flower’s pollinator guild. However, many flowers actively move during their daily cycle, changing both their detectability and accessibility to pollinators. The flowers of the wild tobacco Nicotiana attenuata orientate their corolla upwards at sunset and downwards after sunrise. Here, we investigated the effect of different flower orientations on a major pollinator of N. attenuata, the hawkmoth Manduca sexta. We found that although flower orientation influenced the flight altitude of the moth in respect to the flower, it did not alter its overall attractiveness. These behavioral observations were consistent with the finding that orientation did not systematically change the spatial distribution of floral volatiles, which are major attractants for moths. Moreover, moths invested the same amount of time into probing flowers at different orientations, even though they were only able to feed and take up pollen from horizontally and upward oriented flowers, but not from downward facing flowers. The orientation of the flower was hence crucial for a successful interaction between N. attenuata and its hawkmoth pollinator. Additionally, we determined potential adverse effects of exposing flowers at different orientations to natural daylight levels, finding that anther temperature of upward oriented flowers was more than 7°C higher than for downward oriented flowers. This increase in temperature likely caused the significantly reduced germination success that was observed for pollen grains from upward oriented flowers in comparison to those of downward and horizontally oriented flowers. These results highlight the importance of flower reorientation to ensure pollen protection, while maintaining the association between flower signals and flower accessibility necessary for a successful interaction of the plant with its insect pollinators.
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