Blue is a very prominent color on Planet Earth. But when it comes to nature, blue is the rarest color of all. Less than 1 in 10 Plants have blue flowers, and far fewer animals are blue. According to scientists, part of the reason is that there is not really a true blue color or pigment in nature and both animals and Plants have to accomplish sophisticated tricks of the light to appear blue.
As an artist would mix colors for Plants, blue is produced by mixing naturally occurring pigments. The most commonly used are the red pigments, also known as anthocyanins, and their appearance can be modified by varying acidity. These modifications, combined with reflected light, can produce some spectacular results in nature. For Plants, it is very difficult to produce the blue color. Some Plants only have evolved to do so when it brings them real benefits like attracting bees or other pollinating insects.
In 2021 January, an international research team led by vision scientist Adrian Dyer published their research report based on questions like—why does blue seem to be so rare in the Plant and animal kingdom? And why is it that humans are so fascinated by the color blue? The research team discovered that the scarcity of blue flowers is partly due to the limits of humans’ eyes. From a bee’s perspective, attractive bluish flowers are much more common.
Why do humans are so obsessed with the color blue?
According to a YouGov poll, the color blue is listed as the favorite color for almost every country on Planet Earth. The fact that blue is the rarest color in nature is one of the main reasons behind humans’ obsession with blue color. This is why blue has always been associated with privilege or as a royal color. The ancient Egyptians were fascinated with blue flowers like the blue lotus and struggled with a great deal to decorate objects in blue. They even associated blue with God.
In Hinduism, Vishnu is one of the most important gods in the Hindu Pantheon and, along with Brahma and Shiva, is considered a member of the holy trinity of Sanatana Dharma. Vishnu is the preserver and guardian of humanity, He protects the order of law ( Dharma), and when necessary, he appears on the Earth in various incarnations or Avatars to fight demons and fierce creatures and to maintain Cosmic Harmony. Vishnu’s most familiar avatar Rama and Krishna, are also depicted as deep blue skin.
Color preferences in humans are often subconsciously influenced by important environmental factors in their lives. An ecological interpretation for humans’ common preference for blue is that it is the color of clear sky and bodies of clean water, which are signs of good conditions. Though both sky and sea seem blue, actually both of them are colorless, which indicates the color blue is a mystery.
What about blue flowers?
The research team used a new online Plant database to survey the relative frequencies of blue flowers compared to other colors. They discovered that none were blue among flowers that are pollinated without the mediation of bees or other insects scientifically known as abiotic pollination. When they looked at flowers that needed to attract bees and other insects to transfer their pollen around, they began to see some blue.
This demonstrates that blue flowers evolved to facilitate efficient pollination. Even then, the availability of blue flowers remains relatively rare, which suggests it is difficult for Plants to produce such colors and may be a valuable marker of Plant-pollinator fitness in an environment.
Humans perceive color due to how eyes and brains work. Humans’ visual systems typically have three types of cone photoreceptors that each capture light of different wavelengths: red, green, and blue from the visible spectrum. Humans’ brains then compare information from these receptors to create a perception of color.
For the flowers pollinated by insects, especially bees, it is fascinating to consider that they have a different color vision from humans. Bees’ photoreceptors are sensitive to blue, ultraviolet, and green wavelengths, and they also show a preference for “bluish” colors. The reason why bees have a preference for bluish flowers still remains an open field of research.
Flowers design ‘blue halo’ optical trick to attract bees
Based on the evidence, it is now a fact that wild bees prefer flowers in the violet to the blue range because these blossoms tend to create high concentrated nectar. But it is not easy for Plants to produce blue-colored flowers.
In 2017, a study conducted by the University of Cambridge demonstrated that many Plants have evolved into designing “blue halos” in their flowers to allure bees instead of producing blue flowers. A nanoscale structure on the flower petals produces a blue glow when light hits them. This blue halo is designed with tiny, irregular striations—typically lined up in parallel fashion and is found in all major groups of flowering Plants pollinated by insects.
The research team confirmed these findings with scanning electron microscopy to examine every type of flowering Plant, including grasses, shrubs, herbaceous Plants, and Trees. The spacing and size of the nanoscale structures vary considerably, yet they all generate an ultraviolet (UV) or blue scattering effect particularly attractive to bees, which have enhanced photoreceptor activity in the blue-UV parts of the spectrum.
Why understanding blue flowers are important
The USDA estimated that 80% of insect crop pollination is accomplished by bees. Scientists consider bees to be the keystone species. They are so essential to an ecosystem that the whole ecosystem will collapse without them. At least 90 commercially produced crops depend upon bee pollination for survival. Without bees, there would be no Almonds, Apples, Blueberries, Cherries, Avocados, Cucumbers, Onions, Grapefruit, Oranges, and Pumpkins. Most of them would also disappear without bees. Bees are the unquestioned champions of the pollination world. And their sight is their secret weapon.
The potential of flowering Plants to produce blue colors is linked to land-use intensity, including human-induced factors like artificial fertilization, mowing, and grazing that reduce the frequency of blue flowers. In contrast, more stressful environments appear to have relatively more blue floral colors to provide resilience.
For example, despite the apparent rarity of blue colors in nature, scientists observed that in harsh atmospheres such as in the mountains of the Himalayas, blue flowers were more common than expected. This shows that Plants may have to invest a lot to lure the few available and essential bee pollinators in rough and tough environments. Blue flowers thus appear to exist to best advertise to bee pollinators when competition for pollination services is high.
Conclusion
There is an ongoing debate about which came first, bees or flowers? Scientific evidence suggests that bees were there before the flowering Plants took over the land. And at some point, they coevolved together, which indicates that they both understood each other. Primitive angiosperms or flowering Plants probably took advantage of bee and wasp behavior by producing various colors of flowers as a pollination strategy to compete with gymnosperms or seed-producing Plants. Over time, most of the insects actually shifted to flowering Plants from gymnosperms.
In evolutionary history, angiosperms may well be late bloomers as far as bees are concerned, but with the help of a lot of workaholic bees, they have certainly thrived. Now there are 250,000 species of angiosperms, compared with fewer than 15,000 remaining varieties of gymnosperms.
References
- Binkenstein, J., Renoult, J.P. & Schaefer, H.M. (2013). Increasing land-use intensity decreases the floral color diversity of Plant communities in temperate grasslands. Oecologia, [online] Volume, 173, p. 461–471. Available at: https://doi.org/10.1007/s00442-013-2627-6 [Accessed 9th October 2021].
- Dyer, G. A., et al. (2021). Fragmentary Blue: Resolving the Rarity Paradox in Flower Colors. Frontiers in Plant Science, [online] Available at: https://doi.org/10.3389/fpls.2020.618203 [Accessed 9th October 2021].
- Kantsa, A. & Dyer, A. (2018). Plants use advertising-like strategies to attract bees with color and scent. [online] Available at: https://phys.org/news/2018-04-advertising-like-strategies-bees-colour-scent.html [Accessed 9th October 2021].
- Moyroud, E., Wenzel, T., Middleton, R. et al. (2017). Disorder in convergent floral nanostructures enhances signaling to bees. Nature 550, 469–474. Available at: https://doi.org/10.1038/nature24285 [Accessed 9th October 2021].
- Palmer, E. S., et al. (2013). Visual Aesthetics and Human Preference. Annual Review of Psychology, [online] Volume, 64, p. 77-107. Available at: https://doi.org/10.1146/annurev-psych-120710-100504 [Accessed 9th October 2021].
