̽��ֱ�� of Cambridge - colour

̽��ֱ��artist who made ink from Newton's Apple Tree

lw355 — Mon, 16 Oct 2023 07:11:26 +0000

Nabil Ali is discovering the natural colours hidden within the berries, blooms and bark found in the Cambridge ̽��ֱ�� Botanic Garden – including from a very special tree.

Computational modelling explains why blues and greens are brightest colours in nature

sc604 — Thu, 10 Sep 2020 23:01:01 +0000

̽��ֱ��researchers, from the ̽��ֱ�� of Cambridge, used a numerical experiment to determine the limits of matt structural colour – a phenomenon which is responsible for some of the most intense colours in nature – and found that it extends only as far as blue and green in the visible spectrum. ̽��ֱ��results, published in PNAS, could be useful in the development of non-toxic paints or coatings with intense colour that never fades.

Structural colour, which is seen in some bird feathers, butterfly wings or insects, is not caused by pigments or dyes, but internal structure alone. ̽��ֱ��appearance of the colour, whether matt or iridescent, will depending on how the structures are arranged at the nanoscale.

Ordered, or crystalline, structures result in iridescent colours, which change when viewed from different angles. Disordered, or correlated, structures result in angle-independent matt colours, which look the same from any viewing angle. Since structural colour does not fade, these angle-independent matt colours would be highly useful for applications such as paints or coatings, where metallic effects are not wanted.

“In addition to their intensity and resistance to fading, a matt paint which uses structural colour would also be far more environmentally-friendly, as toxic dyes and pigments would not be needed,” said first author Gianni Jacucci from Cambridge’s Department of Chemistry. “However, we first need to understand what the limitations are for recreating these types of colours before any commercial applications are possible.”

“Most of the examples of structural colour in nature are iridescent – so far, examples of naturally-occurring matt structural colour only exist in blue or green hues,” said co-author Lukas Schertel. “When we’ve tried to artificially recreate matt structural colour for reds or oranges, we end up with a poor-quality result, both in terms of saturation and colour purity.”

̽��ֱ��researchers, who are based in the lab of Dr Silvia Vignolini, used numerical modelling to determine the limitations of creating saturated, pure and matt red structural colour.

̽��ֱ��researchers modelled the optical response and colour appearance of nanostructures, as found in the natural world. They found that saturated, matt structural colours cannot be recreated in the red region of the visible spectrum, which might explain the absence of these hues in natural systems.

“Because of the complex interplay between single scattering and multiple scattering, and contributions from correlated scattering, we found that in addition to red, yellow and orange can also hardly be reached,” said Vignolini.

Despite the apparent limitations of structural colour, the researchers say these can be overcome by using other kinds of nanostructures, such as network structures or multi-layered hierarchical structures, although these systems are not fully understood yet.

Reference:
Gianni Jacucci et al. ‘ ̽��ֱ��limitations of extending nature’s colour palette in correlated, disordered systems.’ PNAS (2020). DOI: 10.1073/pnas.2010486117

Researchers have shown why intense, pure red colours in nature are mainly produced by pigments, instead of the structural colour that produces bright blue and green hues.

In addition to their intensity and resistance to fading, a matt paint which uses structural colour would also be far more environmentally-friendly, as toxic dyes and pigments would not be needed

Gianni Jacucci

will zhang from Pixabay

Macaw

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Metallic blue fruits use fat to produce colour and signal a treat for birds

sc604 — Thu, 06 Aug 2020 15:00:00 +0000

̽��ֱ��plant, Viburnum tinus, is an evergreen shrub widespread across the UK and the rest of Europe, which produces metallic blue fruits that are rich in fat. ̽��ֱ��combination of bright blue colour and high nutritional content make these fruits an irresistible treat for birds, likely increasing the spread of their seeds and contributing to the plant’s success.

̽��ֱ��researchers, led by the ̽��ֱ�� of Cambridge, used electron microscopy to study the structure of these blue fruits. While there are other types of structural colour in nature – such as in peacock feathers and butterfly wings – this is the first time that such a structure has been found to incorporate fats, or lipids. ̽��ֱ��results are reported in the journal Current Biology.

“Viburnum tinus plants can be found in gardens and along the streets all over the UK and throughout much of Europe — most of us have seen them, even if we don’t realise how unusual the colour of the fruits is,” said co-first author Rox Middleton, who completed the research as part of her PhD at Cambridge’s Department of Chemistry.

Most colours in nature are due to pigments. However, some of the brightest and most colourful materials in nature – such as peacock feathers, butterfly wings and opals – get their colour not from pigments, but from their internal structure alone, a phenomenon known as structural colour. Depending on how these structures are arranged and how ordered they are, they can reflect certain colours, creating colour by the interaction between light and matter.

“I first noticed these bright blue fruits when I was visiting family in Florence,” said Dr Silvia Vignolini from Cambridge’s Department of Chemistry, who led the research. “I thought the colour was really interesting, but it was unclear what was causing it.”

“ ̽��ֱ��metallic sheen of the Viburnum fruits is highly unusual, so we used electron microscopy to study the structure of the cell wall,” said co-first author Miranda Sinnott-Armstrong from Yale ̽��ֱ��. “We found a structure unlike anything we’d ever seen before: layer after layer of small lipid droplets.”

̽��ֱ��lipid structures are incorporated into the cell wall of the outer skin, or epicarp, of the fruits. In addition, a layer of dark red anthocyanin pigments lies underneath the complex structure, and any light that is not reflected by the lipid structure is absorbed by the dark red pigment beneath. This prevents any backscattering of light, making the fruits appear even more blue.

̽��ֱ��researchers also used computer simulations to show that this type of structure can produce exactly the type of blue colour seen in the fruit of Viburnum. Structural colour is common in certain animals, especially birds, beetles, and butterflies, but only a handful of plant species have been found to have structurally coloured fruits.

While most fruits have low fat content, some – such as avocadoes, coconuts and olives – do contain lipids, providing an important, energy-dense food source for animals. This is not a direct benefit to the plant, but it can increase seed dispersal by attracting birds.

̽��ֱ��colour of the Viburnum tinus fruits may also serve as a signal of its nutritional content: a bird could look at a fruit and know whether it is rich in fat or in carbohydrates based on whether or not it is blue. In other words, the blue colour may serve as an ‘honest signal’ because the lipids produce both the signal (the colour) and the reward (the nutrition).

“Honest signals are rare in fruits as far as we know,” said Sinnott-Armstrong. “If the structural colour of Viburnum tinus fruits are in fact honest signals, it would be a really neat example where colour and nutrition come at least in part from the same source: lipids embedded in the cell wall. We’ve never seen anything like that before, and it will be interesting to see whether other structurally coloured fruits have similar nanostructures and similar nutritional content.”

One potential application for structural colour is that it removes the need for unusual or damaging chemical pigments – colour can instead be formed out of any material. “It’s exciting to see that principle in action – in this case the plant uses a potentially nutritious lipid to make a beautiful blue shimmer. It might inspire engineers to make double-use colours of our own,” said Middleton, who is now based at the ̽��ֱ�� of Bristol.

̽��ֱ��research was supported in part by the European Research Council, the EPSRC, the BBSRC and the NSF.

Reference:
Rox Middleton et al. ‘Viburnum tinus Fruits Use Lipid to produce Metallic Blue Structural Colour.’ Current Biology (2020). DOI: 10.1016/j.cub.2020.07.005

Researchers have found that a common plant owes the dazzling blue colour of its fruit to fat in its cellular structure, the first time this type of colour production has been observed in nature.

I first noticed these bright blue fruits when I was visiting family in Florence. I thought the colour was really interesting, but it was unclear what was causing it

Silvia Vignolini

What gives this metallic blue fruit its colour?

Rox Middleton

Viburnum tinus fruits

Yes

Ultra-white coating modelled on beetle scales

sc604 — Tue, 13 Mar 2018 11:04:00 +0000

̽��ֱ��material – which is 20 times whiter than paper – is made from non-toxic cellulose and achieves such bright whiteness by mimicking the structure of the ultra-thin scales of certain types of beetle. ̽��ֱ��results are reported in the journal Advanced Materials.

Bright colours are usually produced using pigments, which absorb certain wavelengths of light and reflect others, which our eyes then perceive as colour.

To appear as white, however, all wavelengths of light need to be reflected with the same efficiency. Most commercially-available white products – such as sun creams, cosmetics and paints – incorporate highly refractive particles (usually titanium dioxide or zinc oxide) to reflect light efficiently. These materials, while considered safe, are not fully sustainable or biocompatible.

In nature, the Cyphochilus beetle, which is native to Southeast Asia, produces its ultra-white colouring not through pigments, but by exploiting the geometry of a dense network of chitin – a molecule which is also found in the shells of molluscs, the exoskeletons of insects and the cell walls of fungi. Chitin has a structure which scatters light extremely efficiently – resulting in ultra-white coatings which are very thin and light.

“White is a very special type of structural colour,” said paper co-author Olimpia Onelli, from Cambridge’s Department of Chemistry. “Other types of structural colour – for example butterfly wings or opals – have a specific pattern in their structure which results in vibrant colour, but to produce white, the structure needs to be as random as possible.”

̽��ֱ��Cambridge team, working with researchers from Aalto ̽��ֱ�� in Finland, mimicked the structure of chitin using cellulose, which is non-toxic, abundant, strong and bio-compatible. Using tiny strands of cellulose, or cellulose nanofibrils, they were able to achieve the same ultra-white effect in a flexible membrane.

By using a combination of nanofibrils of varying diameters, the researchers were able to tune the opacity, and therefore the whiteness, of the end material. ̽��ֱ��membranes made from the thinnest fibres were more transparent, while adding medium and thick fibres resulted in a more opaque membrane. In this way, the researchers were able to fine-tune the geometry of the nanofibrils so that they reflected the most light.

“These cellulose-based materials have a structure that’s almost like spaghetti, which is how they are able to scatter light so well,” said senior author Dr Silvia Vignolini, also from Cambridge’s Department of Chemistry. “We need to get the mix just right: we don’t want it to be too uniform, and we don’t want it to collapse.”

Like the beetle scales, the cellulose membranes are extremely thin: just a few millionths of a metre thick, although the researchers say that even thinner membranes could be produced by further optimising their fabrication process. ̽��ֱ��membranes scatter light 20 to 30 times more efficiently than paper and could be used to produce next-generation efficient bright sustainable and biocompatible white materials.

̽��ֱ��research was funded in part by the UK Biotechnology and Biological Sciences Research Council and the European Research Council. ̽��ֱ��technology has been patented by Cambridge Enterprise, the ̽��ֱ��’s commercialisation arm.

Reference:
Matti S. Toivonen et al. ‘Anomalous-Diffusion-Assisted Brightness in White Cellulose Nanofibril Membranes.’ Advanced Materials (2018). DOI: 10.1002/adma.201704050

Researchers have developed a super-thin, non-toxic, lightweight, edible ultra-white coating that could be used to make brighter paints and coatings, for use in the cosmetic, food or pharmaceutical industries.

These cellulose-based materials have a structure that’s almost like spaghetti, which is how they are able to scatter light so well.

Silvia Vignolini

Olimpia Onelli

Cyphochilus beetle with cellulose-based coating

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

In living colour: Brightly-coloured bacteria could be used to 'grow' paints and coatings

sc604 — Tue, 20 Feb 2018 09:06:20 +0000

̽��ֱ��study is a collaboration between the ̽��ֱ�� of Cambridge and Dutch company Hoekmine BV and shows how genetics can change the colour, and appearance, of certain types of bacteria. ̽��ֱ��results open up the possibility of harvesting these bacteria for the large-scale manufacturing of nanostructured materials: biodegradable, non-toxic paints could be 'grown' and not made, for example.

Flavobacterium is a type of bacteria that packs together in colonies that produce striking metallic colours, which come not from pigments, but from their internal structure, which reflects light at certain wavelengths. Scientists are still puzzled as to how these intricate structures are genetically engineered by nature, however.

"It is crucial to map the genes responsible for the structural colouration for further understanding of how nanostructures are engineered in nature," said first author Villads Egede Johansen, from Cambridge's Department of Chemistry. "This is the first systematic study of the genes underpinning structural colours -- not only in bacteria but in any living system."

̽��ֱ��researchers compared the genetic information to optical properties and anatomy of wild-type and mutated bacterial colonies to understand how genes regulate the colour of the colony.

By genetically mutating the bacteria, the researchers changed their dimensions or their ability to move, which altered the geometry of the colonies. By changing the geometry, they changed the colour: they changed the original metallic green colour of the colony in the entire visible range from blue to red. They were also able to create duller colouration or make the colour disappear entirely.

"We mapped several genes with previously unknown functions and we correlated them to the colonies' self-organisational capacity and their colouration," said senior author Dr Colin Ingham, CEO of Hoekmine BV.

"From an applied perspective, this bacterial system allows us to achieve tuneable living photonic structures that can be reproduced in abundance, avoiding traditional nanofabrication methods," said co-senior author Dr Silvia Vignolini from the Cambridge's Department of Chemistry. "We see a potential in the use of such bacterial colonies as photonic pigments that can be readily optimised for changing colouration under external stimuli and that can interface with other living tissues, thereby adapting to variable environments. ̽��ֱ��future is open for biodegradable paints on our cars and walls -- simply by growing exactly the colour and appearance we want!"

Reference:
Villads Egede Johansen et al. 'Livingcolors: Genetic manipulation of structural color in bacterial colonies.' PNAS (2018). DOI: 10.1073/pnas.1716214115

Researchers have unlocked the genetic code behind some of the brightest and most vibrant colours in nature. ̽��ֱ��paper, published in the journal PNAS, is the first study of the genetics of structural colour - as seen in butterfly wings and peacock feathers - and paves the way for genetic research in a variety of structurally coloured organisms.

This is the first systematic study of the genes underpinning structural colours -- not only in bacteria but in any living system.

Villads Egede Johansen

Dr Colin Ingham (Hoekmine BV)

Colony of the Flavobacterium IR1

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Petals produce a 'blue halo' that helps bees find flowers

fpjl2 — Wed, 18 Oct 2017 09:54:15 +0000

Latest research has found that several common flower species have nanoscale ridges on the surface of their petals that meddle with light when viewed from certain angles.

These nanostructures scatter light particles in the blue to ultraviolet colour spectrum, generating a subtle optical effect that scientists have christened the ‘blue halo’.

By manufacturing artificial surfaces that replicated ‘blue halos’, scientists were able to test the effect on pollinators, in this case foraging bumblebees. They found that bees can see the blue halo, and use it as a signal to locate flowers more efficiently.

While the ridges and grooves on a petal surface line up next to each other “like a packet of dry spaghetti”, when analysing different flower species the researchers discovered these striations vary greatly in height, width and spacing – yet all produce a similar ‘blue halo’ effect.

In fact, even on a single petal these light-manipulating structures were found to be surprisingly irregular. This is a phenomenon physicists describe as ‘disorder’.

̽��ֱ��researchers conclude that these “messy” petal nanostructures likely evolved independently many times across flowering plants, but reached the same luminous outcome that increases visibility to pollinators – an example of what’s known as ‘convergent evolution’.

̽��ֱ��study was conducted by a multidisciplinary team of scientists from the ̽��ֱ�� of Cambridge’s departments of plant sciences, chemistry and physics along with colleagues from the Royal Botanic Gardens Kew and the Adolphe Merkele Institute in Switzerland.

̽��ֱ��findings are published today in the journal Nature.

“We had always assumed that the disorder we saw in our petal surfaces was just an accidental by-product of life – that flowers couldn’t do any better,” said senior author Prof Beverley Glover, plant scientist and director of Cambridge’s Botanic Garden.

“It came as a real surprise to discover that the disorder itself is what generates the important optical signal that allows bees to find the flowers more effectively.”

“As a biologist, I sometimes find myself apologising to physicist colleagues for the disorder in living organisms – how generally messy their development and body structures can seem.”

“However, the disorder we see in petal nanostructures appears to have been harnessed by evolution and ends up aiding floral communication with bees,” Glover said.

All flowering plants belong to the ‘angiosperm’ lineage. Researchers analysed some of the earliest diverging plants from this group, and found no halo-producing petal ridges.

However, they found several examples of halo-producing petals among the two major flower groups (monocots and eudicots) that emerged during the Cretaceous period over 100 million years ago – coinciding with the early evolution of flower-visiting insects, in particular nectar-sucking bees.

“Our findings suggest the petal ridges that produce ‘blue halos’ evolved many times across different flower lineages, all converging on this optical signal for pollinators,” said Glover.

Species which the team found to have halo-producing petals included Oenothera stricta (a type of Evening Primrose), Ursinia speciosa (a member of the Daisy family) and Hibiscus trionum (known as ‘Flower-of-the-hour’).

All the analysed flowers revealed significant levels of apparent ‘disorder’ in the dimensions and spacing of their petal nanostructures.

“ ̽��ֱ��huge variety of petal anatomies, combined with the disordered nanostructures, would suggest that different flowers should have different optical properties,” said Dr Silvia Vignolini, from Cambridge’s Department of Chemistry, who led the study’s physics team.

“However, we observed that all these petal structures produce a similar visual effect in the blue-to-ultraviolet wavelength region of the spectrum – the blue halo.”

Previous studies have shown that many species of bee have an innate preference for colours in the violet-blue range. However, plants do not always have the means to produce blue pigments.

“Many flowers lack the genetic and biochemical capability to manipulate pigment chemistry in the blue to ultraviolet spectrum,” said Vignolini. “ ̽��ֱ��presence of these disordered photonic structures on their petals provides an alternative way to produce signals that attract insects.”

̽��ֱ��researchers artificially recreated ‘blue halo’ nanostructures and used them as surfaces for artificial flowers. In a “flight arena” in a Cambridge lab, they tested how bumblebees responded to surfaces with and without halos.

Their experiments showed that bees can perceive the difference, finding the surfaces with halos more quickly – even when both types of surfaces were coloured with the same black or yellow pigment.

Using rewarding sugar solution in one type of artificial flower, and bitter quinine solution in the other, the scientists found that bees could use the blue halo to learn which type of surface had the reward.

“Insect visual systems are different to human ones,” explains Edwige Moyroud, from Cambridge’s Department of Plant Sciences and the study’s lead author. “Unlike us, bees have enhanced photoreceptor activity in the blue-UV parts of the spectrum.”

“Humans can identify some blue halos – those emanating from darkly pigmented flowers. For example the ‘black’ tulip cultivar, known as ‘Queen of the night’.”

“However, we can’t distinguish between a yellow flower with a blue halo and one without – but our study found that bumblebees can,” she said.

̽��ֱ��team say the findings open up new opportunities for the development of surfaces that are highly visible to pollinators, as well as exploring just how living plants control the levels of disorder on their petal surfaces. “ ̽��ֱ��developmental biology of these structures is a real mystery,” added Glover.

New study finds “messy” microscopic structures on petals of some flowers manipulate light to produce a blue colour effect that is easily seen by bee pollinators. Researchers say these petal grooves evolved independently multiple times across flowering plants, but produce the same result: a floral halo of blue-to-ultraviolet light.

̽��ֱ��disorder we see in petal nanostructures appears to have been harnessed by evolution and ends up aiding floral communication with bees

Beverley Glover

Tobias Wenzel/ Edwige Moyroud

Top: petals of Ursinia speciosa, a daisy, contain a dark pigment that appears blue due to 'disordered' striations. Bottom: close-up top and side view of microscopic striations.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

History reveals the hazards of dismantling trade protection

amb206 — Tue, 31 Jan 2017 13:10:54 +0000

American farmers and food producers are said to be licking their lips at the trade opportunities opening up as Britain exits the single European market. But is the British public ready to consume chickens cleaned with chlorine, more genetically modified crops, fizzy drinks made with brominated vegetable oils (emulsifiers), or beef produced with growth-promoting hormones?

Practices such as these are currently prohibited in the EU, leading to a situation where health-related legislation, backed by scientific claims, acts as an effective trade barrier against US food products. Also citing scientifically verified health concerns, the USA has, in turn, banned EU-produced beef for decades after a series of BSE (or Mad Cow Disease) scares in the 1990s. While both continents will continue to use scientific claims to justify trade controls, where does the UK stand with its free trade aspirations?

Scientific claims surrounding the safety of food processing techniques are nothing new. Indeed, the use of new chemical food ingredients in 19th-century food provides one of the earliest examples of how governments and businesses appeal to science and scientists to help protect trade from foreign competition.

Aniline and azo dyes, produced for Europe’s booming 19th-century textile industry, were among the first commercial commodities, including drugs, perfumes and flavourings, which chemists began to synthesise. These chemicals were produced on an industrial-scale from coal-tar, a waste product of the gas industry.

̽��ֱ��new synthetic dyes, whose commercial potential was first recognised by Britain’s William Perkin in 1856, were greeted by the Victorian press as ‘wonders’ of science. Within a few years, they began to be used to colour a wide range of food products such as butter, margarine, milk, wines, noodles, jams and confectionery.

̽��ֱ��mid-19th century was a period when food adulteration was of considerable social concern. Growing public distrust surrounded the provenance of food and its growing industrialisation. Governments and municipal authorities in Britain, continental Europe and the USA appointed chemists to test for food adulteration, while food producers recruited chemists to improve their food processing techniques and to fend off accusations of food manipulation.

While general awareness of the use of textile dyes in food increased, and reports of their possible toxicity emerged, health activists, politicians and businessmen turned to chemists to find answers. Chemists, however, were unable to agree on accurate methods to detect these new chemical substances in food or to assess their toxicity.

Many chemists believed the new dyes were preferable to the toxic metals and minerals – such as lead, copper and arsenic – previously used to colour food. These chemists argued that the new synthetic dyes were a harmless and scientific way to colour and preserve food, helping to increase the range and variety of food available to the public. Other chemists, however, claimed that the safety of the new dyes was not established, and that they were being used illicitly to disguise the quality of food products and deceive the consumer.

A lack of scientific consensus, differing political ideologies and successful lobbying by specific business groups led to a geographically divergent regulatory response. Germany was one the first countries to introduce legislation.

By 1887 Germany was the world’s leading producer of chemical dyes, and its chemical industry was a key constituent of its growing industrial economy. It was certainly in the interest of Germany, and German chemists and industrialists, to maintain public confidence in the new chemical substances being produced by companies such as BASF, Bayer and Hoechst. To strengthen public trust in the new chemicals, Germany and several other European countries, chose to ban a limited number of specified aniline dyes considered to be toxic.

This form of regulation meant that hundreds of other aniline and azo dyes not named in the legislation could be marketed as ‘harmless’ and used in food production, despite the fact that the health effects of most of the legally allowed dyes had never been assessed. As a result, chemical food additives effectively became legitimised as a result of legislation aimed to protect the consumer.

̽��ֱ��USA, meanwhile, opted for a different and more precautionary approach. It was an approach that reinforced the use of the new textile dyes in food and proved beneficial for US businesses.

Instead of banning a few dyes known to be toxic, the US government recommended the use of just seven specified dyes for food colouring. All seven dyes had to be certified by the US government. This strategy, which effectively opened up a new legitimised and specialised market for food dyes, was eagerly embraced by US chemical companies as an opportunity to differentiate themselves from their bigger European competitors.

Meanwhile, Britain, in pursuing laissez faire, free-market trade policies, opted for no prescriptive legislation. ̽��ֱ��British government relied on general food law that prohibited the use of food ingredients capable of poisoning or being used to defraud the consumer, without specifying any particular substances.

As detecting the use of the new dyes in food was almost impossible, and because there was little scientific consensus as to which dyes were harmful, this form of legislation effectively resulted in chemical substances becoming increasingly used, but rarely disclosed, as food ingredients.

In the late 19th century, the use of chemical dyes in food lay at the heart of a negotiation between freedom of trade, consumer choice and the support of commercial practices versus consumer protection, public health and greater transparency.

Legislation, allegedly based on science, failed to resolve the controversies surrounding the risks and benefits of chemical food additives, which remain the focus of considerable debate 150 years later. Instead, regulations, designed to protect public health, acted as trade barriers used to protect domestic businesses.

Although the regulatory list of permitted and safe food ingredients used today in Europe, so-called E-numbers, is more like the original regulatory approach adopted by the US in 1906, there is still a significant difference in opinion between European and US regulators, businesses and scientists as to which chemicals can be safely used in food.

History shows that interested parties invoke science for different purposes, whether consumer groups trying to protect public health or business trying to stave off competition. For the country’s future physical and economic health, the British public and British businesses need to keep a watchful eye on future trade talks between President Trump and Prime Minister May as Britain exits the trade and regulatory regime of the EU.

Carolyn Cobbold took her PhD at Cambridge ̽��ֱ��'s Faculty of History.

As the UK prepares to leave the EU, trade regimes are being reconfigured. Research into 19th-century trade regulations by Carolyn Cobbold, historian of science, shows that scientific claims play a significant role in shaping international trade. She urges us to heed the lessons of the past.

Is the British public ready to consume chickens cleaned with chlorine, more genetically modified crops, or beef produced with growth-promoting hormones?

illuminating 9_11

GM sweetcorn

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Flowers tone down the iridescence of their petals and avoid confusing bees

jeh98 — Thu, 25 Feb 2016 17:04:02 +0000

Iridescent flowers are never as dramatically rainbow-coloured as iridescent beetles, birds or fish, but their petals produce the perfect signal for bees, according to a new study published today in Current Biology.

Bees buzzing around a garden, looking for nectar, need to be able to spot flower petals and recognise which coloured flowers are full of food for them. Professor Beverley Glover from the ̽��ֱ�� of Cambridge’s Department of Plant Sciences and Dr Heather Whitney from the ̽��ֱ�� of Bristol found that iridescence – the shiny, colour-shifting effect seen on soap bubbles – makes flower petals more obvious to bees, but that too much iridescence confuses bees’ ability to distinguish colours.

Whitney, Glover and their colleagues found that flowers use more subtle, or imperfect, iridescence on their petals, which doesn’t interfere with the bees’ ability to distinguish subtly different colours, such as different shades of purple. Perfect iridescence, for example as found on the back of a CD, would make it more difficult for bees to distinguish between subtle colour variations and cause them to make mistakes in their flower choices.

“In 2009 we showed that some flowers can be iridescent and that bees can see that iridescence, but since then we have wondered why floral iridescence is so much less striking than other examples of iridescence in nature,” says Glover. “We have now discovered that floral iridescence is a trade-off that makes flower detection by bumblebees easier, but won’t interfere with their ability to recognise different colours.”

Bees use ‘search images’, based on previously-visited flowers, to remember which coloured flowers are a good source of nectar.

“On each foraging trip a bee will usually retain a single search image of a particular type of flower,” explains Glover, “so if they find a blue flower that is rich in nectar, they will then visit more blue flowers on that trip rather than hopping between different colours. If you watch a bee on a lavender plant, for example, you’ll see it visit lots of lavender flowers and then fly away – it won’t usually move from a lavender flower to a yellow or red flower.”

This colour recognition is vital for both the bees and the plants, which rely on the bees to pollinate them. If petals were perfectly iridescent, then bees could struggle to identify and recognise which colours are worthwhile visiting for nectar – instead, flowers have developed an iridescence signal that allows them to talk to bees in their own visual language.

̽��ֱ��researchers created replica flowers that were either perfectly iridescent (using a cast of the back of a CD), imperfectly iridescent (using casts of natural flowers), or non-iridescent. They then tested how long it took for individual bees to find the flowers.

They found that the bees were much quicker to locate the iridescent flowers than the non-iridescent flowers, but it didn’t make a difference whether the flowers were perfectly or imperfectly iridescent. ̽��ֱ��bees were just as quick to find the replicas modelled on natural petals as they were to find the perfectly iridescent replicas.

When they tested how fast the bees were to find nectar-rich flowers amongst other, similarly-coloured flowers, they found that perfect iridescence impeded the bees’ ability to distinguish between the flowers – the bees were often confused and visited the similarly-coloured flowers that contained no nectar. However, imperfect iridescence, found on natural petals, didn’t interfere with this ability, and the bees were able to successfully locate the correct flowers that were full of nectar.

“Bees are careful shoppers in the floral supermarket, and floral advertising has to tread a fine line between dazzling its customers and being recognisable,” says Lars Chittka from Queen Mary ̽��ֱ�� of London, another co-author of the study.

“To our eyes most iridescent flowers don’t look particularly striking, and we had wondered whether this is simply because flowers aren’t very good at producing iridescence,” says Glover. “But we are not the intended target – bees are, and they see the world differently from humans.”

“There are lots of optical effects in nature that we don’t yet understand. We tend to assume that colour is used for either camouflage or sexual signalling, but we are finding out that animals and plants have a lot more to say to the world and to each other.”

Glover and her colleagues are now working towards developing real flowers that vary in their amount of iridescence so that they can examine how bees interact with them.

“ ̽��ֱ��diffraction grating that the flowers produce is not as perfectly regular as those we can produce on things like CDs, but this 'advantageous imperfection' appears to benefit the flower-bee interaction,” says Whitney.

Reference: Whitney, Heather et al “Flower Iridescence Increases Object Detection in the Insect Visual System without Compromising Object Identity” Current Biology (2016). DOI: https://dx.doi.org/10.1016/j.cub.2016.01.026

Professor Glover will be giving the talk 'Can we improve crop pollination by breeding better flowers?' at the Cambridge Science Festival on Sunday 20 March 2016. More information can be found here: http://www.sciencefestival.cam.ac.uk/events/can-we-improve-crop-pollinat...

Inset images: Iridescent flower (Copyright Howard Rice); Bee on non-iridescent flower (Edwige Moyroud); Bee on non-iridescent flower (Edwige Moyroud).

Latest research shows that flowers’ iridescent petals, which may look plain to human eyes, are perfectly tailored to a bee’s-eye-view.

There are lots of optical effects in nature that we don’t yet understand... we are finding out that animals and plants have a lot more to say to the world and to each other

Beverley Glover

Bee on a non-iridescent flower

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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