Flower movement balances pollinator needs and pollen protection

Flower signaling and orientation are key characteristics that 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 upward at sunset and downward 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 the moth's final flower choice. 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 the moths. Moreover, hawkmoths invested the same amount of time into probing flowers at different orientations, even though they were only able to feed and gather 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 also investigated 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 balance pollen protection and a successful interaction of the plant with its insect pollinators by maintaining the association between flower volatiles and flower accessibility to the pollinator. Detecting and subsequently being able to handle a certain flower are two key steps in the interaction between pollinators and plants (Harder 1985, Riffell et al. 2014). However, the detectability and accessibility of a flower for a pollinator might vary, as some flowers actively open and close or alter their orientation during the course of the day (Atamian et al. 2016). It has been argued that flowers perform these movements to balance pollinator attraction and the protection of nectar and pollen (Aizen 2003, Yon et al. 2017). However, in spite of its potential importance for both the plant and the pollinator, experimental evidence