Plant & zo
The science of plants and more
UV pigmentation, more than just for the bees
Flowers come in many shapes and colours. Beyond even those we can see. Flowers show a lot of variation in, for us invisible, ultraviolet pigments. Such as the UV absorbing pigments on the petals of sunflowers. These can be just at the base of the petal, forming a small UV absorbing circle. But they can also cover the complete petal, making a large UV absorbing circle. Or anywhere in between these two extremes. Researchers from Canada found out what is the basis of this variation.
In contrast to what was expected, the pollinators were not responsible. These have a strong preference for flowers with an average to large UV absorbing circle. But if it was only the pollinators calling the shots, then there would not have been any flowers with small UV absorbing circles.
Two different aspects influenced UV pigmentation. First, the temperature. The lower the average temperature, the larger the UV absorbing circle. A large UV absorbing surface is heating up more quickly, and bees love warm flowers.
Secondly, relative humidity. By low relative humidity a plant has a higher transpiration rate, so the plant loses more water. This is something wants to avoid. One of the substances that helps a plant to protect against drought stress are UV absorbing pigments. Therefore, a bigger UV absorbing surface result in less wilted plants.
So even though bees and other pollinators use UV pigmentation to coordinate their landing on flowers. Sunflowers make UV absorbing pigments firstly to control their temperature and water loss. That bees find them useful is a side issue.
Todesco M, Bercovich N, Kim A, Imerovski I, Owens GL, Dorado Ruiz Ó, Holalu SV, Madilao LL, Jahani M, Légaré JS, Blackman BK, Rieseberg LH. (2022) Genetic basis and dual adaptive role of floral pigmentation in sunflowers. eLife 11:e72072. doi: 10.7554/eLife.72072
Laurich J, O’Brien AM. (2022) Plants: Why do sunflowers have invisible colors? eLife 2022;11:e76105 doi: 10.7554/eLife.76105