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Abstract:
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 upwardoriented
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.
