The mystery of the blue flower: nature’s rare colour owes its existence to bee vision



Shutterstock

Adrian Dyer, RMIT University

At a dinner party, or in the schoolyard, the question of favourite colour frequently results in an answer of “blue”. Why is it that humans are so fond of blue? And why does it seem to be so rare in the world of plants and animals?

We studied these questions and concluded blue pigment is rare at least in part because it’s often difficult for plants to produce. They may only have evolved to do so when it brings them a real benefit: specifically, attracting bees or other pollinating insects.

We also discovered that the scarcity of blue flowers is partly due to the limits of our own eyes. From a bee’s perspective, attractive bluish flowers are much more common.

A history of fascination

The gold and blue funerary mask of the ancient Egyptian pharaoh Tutankhamun.
The ancient mask of the pharaoh Tutankhamun is decorated with lapis lazuli and turquoise.
Roland Unger / Wikimedia, CC BY-SA

The ancient Egyptians were fascinated with blue flowers such as the blue lotus, and went to great trouble to decorate objects in blue. They used an entrancing synthetic pigment (now known as Egyptian blue) to colour vases and jewellery, and semi-precious blue gemstones such as lapis lazuli and turquoise to decorate important artefacts including the Mask of Tutankhamun.




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Feeling blue? Get acquainted with the history of a colour


Blue dye for fabric is now common, but its roots lie in ancient Peru, where an indigoid dye was used to colour cotton fabric about 6000 years ago. Indigo blue dyes reached Europe from India in the 16th century, and the dyes and the plants that produced them became important commodities. Their influence on human fashion and culture are still felt today, perhaps most obviously in blue jeans and shirts.

Renaissance painters in Europe used ground lapis lazuli to produce dazzling works that captivated audiences.

A painting of a woman in a vivid blue robe and white hood, with bowed head and clasped hands.
The Virgin in Prayer by the Italian painter Sassoferrato, circa 1650, highlights the vivid blue colour made with ground lapis lazuli.

Today many blues are created with modern synthetic pigments or optical effects. The famous blue/gold dress photograph that went viral in 2015 not only shows that blue can still fascinate — it also highlights that colour is just as much a product of our perception as it is of certain wavelengths of light.

Why do humans like blue so much?

Colour preferences in humans are often influenced by important environmental factors in our lives. An ecological explanation for humans’ common preference for blue is that it is the colour of clear sky and bodies of clean water, which are signs of good conditions. Besides the sky and water, blue is relatively rare in nature.

What about blue flowers?

We used a new online plant database to survey the the relative frequencies of blue flowers compared to other colours.

Among flowers which are pollinated without the intervention of bees or other insects (known as abiotic pollination), none were blue.

But when we looked at flowers that need to attract bees and other insects to move their pollen around, we started to see some blue.

This shows blue flowers evolved for enabling efficient pollination. Even then, blue flowers remain relatively rare, which suggests it is difficult for plants to produce such colours and may be a valuable marker of plant-pollinator fitness in an environment.

Global flower colour frequency for human visual perception (A) shows when considering animal pollinated species less than 10% are blue (B), and for wind pollinated flowers almost none are observed to be blue (C).
Dyer et al., Author provided

We perceive colour due to how our eyes and brain work. Our visual system typically has three types of cone photoreceptors that each capture light of different wavelengths (red, green and blue) from the visible spectrum. Our brains then compare information from these receptors to create a perception of colour.

For the flowers pollinated by insects, especially bees, it is interesting to consider that they have different colour vision to humans.




Read more:
Inside the colourful world of animal vision


Bees have photoreceptors that are sensitive to ultraviolet, blue and green wavelengths, and they also show a preference for “bluish” colours. The reason why bees have a preference for bluish flowers remains an open field of research.

Various blue flowers from our study.

Why understanding blue flowers is important

About one-third of our food depends on insect pollination. However, world populations of bees and other insects are in decline, potentially due to climate change, habitat fragmentation, agricultural practices and other human-caused factors.

The capacity of flowering plants to produce blue colours is linked to land use intensity including human-induced factors like artificial fertilisation, grazing, and mowing that reduce the frequency of blue flowers. In contrast, more stressful environments appear to have relatively more blue floral colours to provide resilience.

For example, despite the apparent rarity of blue flower colours in nature, we observed that in harsh conditions such as in the mountains of the Himalaya, blue flowers were more common than expected. This shows that in tough environments plants may have to invest a lot to attract the few available and essential bee pollinators. Blue flowers thus appear to exist to best advertise to bee pollinators when competition for pollination services is high.

Knowing more about blue flowers helps protect bees

Urban environments are also important habitats for pollinating insects including bees. Having bee friendly gardens with flowers, including blue flowers that both we and bees really appreciate, is a convenient, pleasurable and potentially important contribution to enabling a sustainable future. Basically, plant and maintain a good variety of flowers, and the pollinating insects will come.




Read more:
Our ‘bee-eye camera’ helps us support bees, grow food and protect the environment


The Conversation


Adrian Dyer, Associate Professor, RMIT University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids: is the sky blue on other planets?



Unlike Earth’s atmosphere, Jupiter’s ‘sky’ hosts magnificent shades of orange, white, brown and blue.
NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstädt, CC BY-SA

Jake Clark, University of Southern Queensland


Is the sky blue on other planets, like on Earth? What is an atmosphere, and do other planets have one? – Charlie, age 10



G’day Charlie, and thank you so much for your incredibly curious question.

Before I get too excited talking about the atmospheres of other planets, first we have to talk about what an atmosphere actually is.

Earth’s atmosphere is split into different layers.
ESA

The atmosphere is normally the outermost layer of a planet. On rocky worlds like Earth it is usually the lightest and thinnest layer.

The thing that makes an atmosphere an atmosphere is what it’s made of. It’s not made up of big lumps of rocks or huge swirling oceans; it is made up of gases.

What’s in an atmosphere?

Atmospheres can contain a wide variety of gases. Most of Earth’s atmosphere is a gas called nitrogen that doesn’t really react with anything. There’s also a fair bit of oxygen, which is what we need to breathe. There are also two other important gases called argon and carbon dioxide, and tiny amounts of lots of other ones.

The mix of gases is what gives a planet’s atmosphere its colour.




Read more:
Curious Kids: Why is the sky blue and where does it start?


Earth’s atmosphere is made up of gases that tend to bounce blue light in all directions (known as “scattering”) but let most other colours of light straight through. This scattered light is what gives Earth’s atmosphere its blue colour.

Do other planets have blue atmospheres? Some of them sure do!

The blue “haze” surrounding Earth in space is caused by the scattering of light from Earth’s atmosphere.

Other worlds

The atmospheres of the two ice giants in our solar system, Neptune and Uranus, are both beautiful shades of blue.

However, these atmospheres are a different blue than ours. It’s caused by the huge amounts of a gas called methane swirling around.

(Side note: methane is also the main component of farts. That’s right, there’s a layer of farts on Uranus.)

The atmosphere of Uranus (left) is slightly greener than Neptune’s (right).
NASA / JPL-Caltech / Björn Jónsson

Jupiter and Saturn, however, have completely different-coloured atmospheres.

Ice crystals made of a chemical called ammonia in Saturn’s upper atmosphere make it a pale shade of yellow.

Uranus’ atmosphere also contains some ammonia, which makes the planet a slightly greener shade than the deep blue we see on Neptune.

Jupiter’s atmosphere has distinctive brown and orange bands, thanks to gases that may contain the elements phosphorus and sulfur, and possibly even more complicated chemicals called hydrocarbons.**

The Juno spacecraft flying past Jupiter in 2017.

In some extreme cases, the entire planet might just be a huge atmosphere with no rocky surface at all. Astronomers and planetary scientists like myself are still trying to work out whether Jupiter and Saturn have rocky surfaces, deep down in their atmosphere, or whether they’re both simply huge balls of gas.

The Cassini spacecraft took this cracking image of Saturn back in 2010.
NASA/JPL-Caltech/Space Science Institute

However, there are some planets that have no atmosphere at all! The Sun’s closest and smallest neighbour, Mercury, is one example. Its surface is exposed to the vastness of space.

Beyond our solar system

So far I’ve been talking about the atmospheres of planets in our Solar system. But what about planets in other planetary systems, orbiting other stars?

Well, astronomers have been detecting the atmospheres of these planets (which we call “exoplanets”) for the past 20 years! It wasn’t until last year, however, that astronomers managed to detect the atmosphere of a rocky exoplanet. The planet is called LHS 3844b and it’s so far away that the light takes almost 50 years to reach us!

LHS 3844b weighs twice as much as Earth, and we astronomers thought it would have a pretty thick atmosphere. But, to our surprise, it has little to no atmosphere at all! So it might be more like Mercury than Earth.

Animation showing an artist’s impression on what LHS 3844b’s surface may look like.

We still have a lot to learn about far-off planets and discovering one with an Earth-like atmosphere that’s ripe for life is still many years away.

Maybe, Charlie, you could be the first astronomer to detect an Earth-like atmosphere on another world!The Conversation

Jake Clark, PhD Candidate, University of Southern Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.