Tag: colour

A fossil penguin gets its colours

By Ed Yong | September 30, 2010 2:00 pm


All Almost all modern penguins wear a suit of black feathers, but prehistoric members of the group didn’t go for the dinner jacket look. A newly discovered penguin, known as Inkayacu, was dressed in grey and reddish-brown hues.

Inkayacu paracasensis is named after the Quechua words for “water king” and the Paracas National Park where it was discovered by Julia Clarke from the University of Texas. Clarke’s team are no strangers to giant fossil penguins. In 2007, they unveiled two extinct species: Perudyptes, about the size of the modern king penguin; and Icadyptes, which was larger than any living species and had an unusually long, spear-like beak. Like Icadyptes, Inkayacu also swam off the coast of ancient Peru, had a long beak, and was one of the largest penguins in history. It weighed around twice as much as the heaviest of today’s penguins – the emperor.

In many ways, Inkayacu is no more significant a find that Icadyptes was three years ago. It is neither the oldest nor the largest penguin fossil, it doesn’t hail from a new part of the world, and it provides few clues about the group’s evolution. However, it does have one stand-out feature that probably secured its unveiling in the pages of Science – its feathers.

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CATEGORIZED UNDER: Animals, Birds, Palaeontology

The renaissance of technicolour dinosaurs continues (and the gloves come off…)

By Ed Yong | February 4, 2010 2:00 pm


National Geographic should have a 3-D animation up soon

The pursuit of accurate dinosaur colours just turned into a race, and a heated one at that. Just last week, I wrote about a group of scientists who claimed to have accurately identified the colours of some feathered dinosaurs by microscopically analysing three fossils. According to that study, Sinosauropteryx had a tail covered in ginger stripes. Now, another group have revealed the palette of an entire dinosaur, Anchiornis. This tiny predator had a dark grey body and the limbs bore long, white feathers tipped with black spangles. Its head was mostly grey with reddish-orange and black specks, and an extravagant reddish-orange crown.

Both reconstructions are based on microscopic structures called melanosomes. They’re partly responsible for the brilliant colours of modern bird feathers, they’re packed with pigments, and they happen to fossilise well. There are two major types. Spherical ‘phaemelanosomes’ contain a reddish-brown or yellow pigment while the rod-like ‘eumelanosomes’ have black-grey tints.

The technique of inferring colours from fossil melanosomes was pioneered by Jakob Vinther at Yale University. He used it to show that a Cretaceous bird feather probably had black and white stripes and, later, that another fossil feather had an iridescent starling-like sheen. But these were analyses of single papers and even last week’s paper coloured Sinosauropteryx by looking at just one part of a single individual.  

Vinther isn’t impressed with his rivals. “They are in the Stone Age when it comes to understanding melanosome fossilization and interpretation of original colors,” he says. To him, it’s simply not enough predict colours based on the presence of one type of melanosome. Even the hues of single feathers can depend on a mix of the two melanosome types with different concentrations of pigments. So you need to know the distribution of melanosomes across an animal and even then, you still need to work out how that translates to different colours.

And that’s exactly what he’s done. When I spoke to Vinther last week, he said, “We are still far from putting colours on dinosaurs [but] the future is promising. Eventually we will have dinosaurs in technicolour. We are working seriously on that currently.” He wasn’t kidding!

He had been working on a new specimen of Anchiornis with the catchy name of BMNHC PH828. The tail is missing but the rest of the skeleton is beautifully preserved, including the skull and both sets of limbs with their elegant plumes. Rather than looking at individual body parts, Vinther took 29 samples from the specimen, representing every type of feather types across different body parts. In each one, he thoroughly analysed the size, shape, density and distribution of melanosomes.

To interpret this goldmine of data, he worked with his colleague Matt Shawkey to catalogue the melanosomes from a wide variety of living birds, from ravens to finches to mallards. This modern data set was a cross between a paint catalogue and a Rosetta stone. It told Vinther how different combinations of melanosomes led to different colours and allowed him to correctly paint his Anchiornis.

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White horses are less attractive to horseflies

By Ed Yong | February 3, 2010 9:30 am
“That is Shadowfax. He is chief of the Maeras, lords of all horses, and not even Theoden, King of Rohan, has ever looked on a better. Does he not shine like silver, and run as smoothly as a swift stream?” – Gandalf

In the Lord of the Rings, Gandalf rides upon a magnificent white stallion called Shadowfax. White horses have been greatly prized in human societies as a sign of wealth and dignity, largely because their bright coats are both pretty and rare. There are reasons for that. In the wild, the same conspicuousness that inspires legendary tales also makes white horses vulnerable to predators and sensitive to skin cancer. But they have an unexpected benefit – they make horses less attractive to horseflies.

Anyone who has been bitten by a horsefly (formally, a tabanid) knows that they’re much more irritating than your average midge or mosquito. Rather than puncturing skin, their mandibles are designed to rip and shear. As a result, their bites hurt and they can drive grazing animals to distraction. They can also transfer serious diseases, including Equine Infectious Anaemia, parasitic worms, and even anthrax.

Now, Gabor Horvath from Eotvos University, Hungary, has found that white coats are more horsefly-proof than darker ones. They reflect very little polarised light – light vibrating on a single plane – and it’s this light that horseflies use to track down their next blood meal.

On a sunny June day, Horvath watched two horses – one brown and one white – as they grazed in a local field. Both were almost continuously attacked by horseflies and had to defend themselves by tail-swishing, kicking, shuddering, head-swinging, biting, licking and even rolling on the group. But the white horse had the better time of it – photographs revealed that, on average, the brown horse had 3.7 times more horseflies on or near it. Eventually, the attacks were so irritating that the horses were driven into a nearby shady forest, where they gained a temporary respite. Again, the brown horse was always the first to cave and spent longer in the shade.

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CATEGORIZED UNDER: Animals

What colours were dinosaur feathers?

By Ed Yong | January 27, 2010 1:00 pm

Sinosauropteryx.jpg

Dinosaur books have become more colourful affairs of late, with the dull greens, browns and greys of yesteryear replaced by vivid hues, stripes and patterns. This has largely been a question of artistic licence. While fossils may constrain an artist’s hand in terms of size and shape, they haven’t provided any information about colour. But that is starting to change.

The fossils of some small meat-eating dinosaurs were covered in filaments that are widely thought to be the precursors of feathers. And among these filaments, a team of Chinese and British scientists have found the distinctive signs of melanosomes, small structures that are partly responsible for the colours of modern bird feathers.

Melanosomes are packed with melanins, pigments that range from drab blacks and greys to reddish-brown and yellow hues. Their presence in dinosaur filaments has allowed Fucheng Zhang to start piecing together the colours of these animals, millions of years after their extinction. For example, Zhang thinks that the small predator Sinosauropteryx had “chestnut to reddish-brown” stripes running down its tail and probably a similarly coloured crest down its back. Meanwhile, the early bird Confuciusornis had a variety of black, grey, red and brown hues, even within a single feather.

Zhang’s discovery also launches another salvo into a debate over the very nature of “feathered” dinosaurs. Beautiful fossils, mainly from China, show that several species of dinosaur had feathers akin to the flight-capable plumes of modern birds. Species like Caudipteryx and the four-winged Microraptor had true feathers with asymmetric vanes arranged around a central shaft.

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Three desert lizards evolve white skins through different mutations to the same gene

By Ed Yong | December 28, 2009 5:30 pm

In the White Sands National Park of New Mexico, there are three species of small lizard that all share white complexions. In the dark soil of the surrounding landscapes, all three lizards wear coloured coats with an array of hues, stripes and spots. Colours would make them stand out like a beacon among the white sands  so natural selection has bleached their skins. Within the last few thousand years, the lesser earless lizard, the eastern fence lizard and the little striped whiptail have all evolved white forms that camouflage beautifully among the white dunes.

Erica Bree Rosenblum from the University of Idaho has found that their white coats are the result of changes to the same gene, Mc1r. All of these adaptations arose independently of one another and all of them reduce the amount of the dark pigment, melanin, in the lizards’ skin.  It’s a wonderful example of convergent evolution, where the same environmental demands push different species along the same evolutionary paths. But Rosenblum has also found that there are many ways to break a gene.

Each of the three lizards has a different mutation in their Mc1r gene, that has crippled it in diverse ways. These differences may seem slight, but they affect how dominant and widespread the white varieties are, and how likely they are to branch off into new species of their own. Even when different species converge on the same results – in this case, whitened skin – and even when the same gene is responsible, their evolutionary paths can still be very different.

The Mc1r gene encodes a protein called the melanocortin 1 receptor (MC1R). It’s a messenger that sits astride the cell’s membrane and transmits messages across it. It triggers a sequence of events that stimulates the production of the dark pigment melanin. In this way, it affects the skin colour of many animals and faulty copies of the gene tend to result in lighter colours. In humans, for example, around 80% of redheads owe their hair colour to common faulty variant of Mc1r.

In each of the White Sands lizards, just one of the MC1R protein’s many amino acids has been swapped (red circles above), and it’s a different one in each species. All three amino acids lie within the part of the protein that straddles the cell membrane. These regions are important for keeping the protein together, and for channelling signals from one side of the membrane to another.

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CATEGORIZED UNDER: Evolution, Lizards, Reptiles

Discriminating butterflies show how one species could split into two

By Ed Yong | November 5, 2009 2:00 pm

Walk through the rainforests of Ecuador and you might encounter a beautiful butterfly called Heliconius cydno. It’s extremely varied in its colours. Even among one subspecies, H.cydno alithea, you can find individuals with white wingbands and those with yellow. Despite their different hues, they are still the same species… but probably not for much longer.

Even though the two forms are genetically similar and live in the same area, Nicola Chamberlain from Harvard University has found that one of them – the yellow version – has developed a preference for mating with butterflies of its own colour. This fussiness has set up an invisible barrier within the butterfly population, where traits that would typically separate sister species – colour and mate preferences – have started to segregate. In time, this is the sort of change that could split the single species into two.  

Heliconius butterflies defend themselves with foul chemicals and advertise their distasteful arsenal with bright warning colours on their wings. The group has a penchant for diversity, and even closely related species sport different patterns. But the butterflies are also rampant mimics. Distantly related species have evolved uncanny resemblances so that their warnings complement one another – a predator that learns to avoid one species will avoid all the ones that share the same patterns.  It’s a mutual protection racket, sealed with colour.

The result of this widespread mimicry is that populations of the same species can look very different because they are imitating different models. This is the case with H.cydno – the yellow form mimics the related H.eleuchia, while the white form mimics yet another species, H.sapho.

How can we be sure that the pairs of butterflies that look alike aren’t in fact more closely related? For a start, scientists have shown that the frequencies of the yellow and white versions of alithea in the wild match those of the species they mimic. Genetic testing provides the clincher. It confirms that the two mimics are indeed more closely related to each other than they are to their models.

Genetics also tells us how alithea achieves its dual coats. Colour is determined by a single gene; if a butterfly inherits the dominant version, it’s white and if it gets two copies of the recessive one, it’s yellow. Pattern is controlled in a similar way by a second gene. These variations aside, there are no distinct genetic differences between the two alithea forms. They are still very much a single population of interbreeding butterflies.

But that may change, and fussy males could be the catalyst. Chamberlain watched over 1,600 courtship rituals performed by 115 captured males. Her voyeuristic experiments showed that yellow males strongly preferred to mate with yellow females, although white males weren’t so fussy.

This isn’t just a whimsical preference – Chamberlain thinks that the colour gene sits very closely to a gene for mate preference. The two genes may even be one and the same. Either way, their proximity on the butterfly’s genome means that their fates are intertwined and they tend to be inherited as a unit. That’s certainly plausible, for the same pigments that colour the butterflies’ wings also serve to filter light arriving into their eyes. A change in the way those pigments are produced could alter both the butterfly’s appearance and how it sees others of its kind.  

To see what happens when this process goes further, you don’t have to travel far. Costa Rica is home to another H.cydno subspecies called galanthus, and a closely related species called H.pachinus. They represent a further step down the road that alithea is headed down. Galanthus and H.pachinus look very different because they mimic different models – the former has white wingbands reminiscent of H.sapho, while the latter has green bands inspired by H.hewitsoni.

Nonetheless, the two species could interbreed if they ever got the chance. Two things stand in the way. The first is geography – H.cydno galanthus stays on the eastern side of the country, while H.pachinus remains on the west. The second is, as with alithea, sex appeal. Males prefer females bearing the same wing colours as they do so even if the two sexes of the two species were to cross paths, they’d probably fly right past each other.

Genetically, these species have also diverged far further than the two forms of alithea have. They differ at no less than five genes involved in colour and pattern, two of which are practically identical to the ones that causing alithea to segregate. They also provide more evidence that the genes for colour and mate preference are closely linked, for crossbreeding the two species yields offspring with half-way colours and half-way preferences.

These butterflies are by no means the only examples of speciation in the wild. In this blog alone, I’ve discussed a beautiful case study of diversity creating itself among fruit flies and parasitic wasps, explosive bursts of diversity in cichlid fish fuelled by violent males, and a giant predatory bug that’s splitting cavefish into isolated populations.

But Heliconius butterflies may be the most illuminating of all these case studies. They’re easy to capture, breed and work with. And as Chamberlain’s study shows, they can marshal together the contribution of experts in genetics, ecology, evolution and animal behaviour in an effort to understand that most magnificent of topics – the origin of species.

[This post was written as an entry for the NESCENT evolution blogging contest. For more details about this competition, visit their website.]

Reference: Science 10.1126/science.1179141

More on speciation:

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Mantis shrimp eyes outclass DVD players, inspire new technology

By Ed Yong | October 25, 2009 2:00 pm

The most incredible eyes in the animal world can be found under the sea, on the head of the mantis shrimps. Each eye can move independently and can focus on object with three different areas, giving the mantis shrimp “trinocular vision”. While we see in three colours, they see in twelve, and they can tune individual light-sensitive cells depending on local light levels. They can even see a special type of light – ‘circularly polarised light’ – that no other animal can.

But Nicholas Roberts from the University of Bristol has found a new twist to the mantis shrimp’s eye. It contains a technology that’s very similar to that found in CD and DVD players, but it completely outclasses our man-made efforts. If this biological design can be synthesised, it could form the basis of tomorrow’s multimedia players and hard drives.

Previous studies have found that mantis shrimps can detect polarised light – light that vibrates in a single plane as it travels. Think of attaching a piece of string to a wall and shaking it up and down, and you’ll get the idea. Last year, scientists discovered that they can also see circularly polarised light, which travels in the shape of a helix. To date, they are still the only animal that can see these spiralling beams of light.

Its secret lies at a microscopic level. Each eye is packed with light-sensitive cells called rhabdoms that are arranged in groups of eight. Seven sit in a cylinder and each has a tiny slit that polarised light can pass through if it’s vibrating in the right plane. The eighth cell sits on top and its slit is angled at 45 degrees to the seven below it. It’s this cell that converts circularly polarised light into its linear version. 

In technical terms, the eighth cell is a “quarter-wave plate”, because it rotates the plane in which light vibrates. Similar devices are also found in camera filters, CD players and DVD players but these man-made versions are far inferior to the mantis shrimp’s biological tech.

Synthetic wave plates only work well for one colour of light. If you change the wavelength slightly, they become ineffective, so designing a wave plate that works for many colours is exceptionally difficult. But the mantis shrimp has already done it. Its eyes work across the entire visible spectrum, from ultraviolet to infrared, achieving a level of performance that our technology can’t compete with.

What’s more, the same eighth cell not only manipulates circularly polarised light, but it can sense ultraviolet light too. It’s a detector and a converter – a two-for-one deal that nothing man-made shares.

Why the mantis shrimp needs such a sophisticated eye is unclear. It could help them to see their prey more clearly in water, which is rife with circularly polarised reflections. It needs good eyesight to be able to hit its prey accurately. Like a crustacean Thor, mantis shrimps shatter their victims with devastating hammer blows inflicted by the fastest arms on the planet. Their forearms, which end in clubs or spears, can travel through water at 10,000 times the acceleration of gravity and hit with the force of a rifle bullet.

Another option is that their super-eyes allow them to send and receive secret messages. A mantis shrimp’s shell reflects circularly polarised light, and males and females produce these reflections from different body parts. Their ability to see this type of light could give them a hidden channel of communication that only they can see, for use in courtship or combat.

Whatever the reason for it, Roberts thinks that the eye’s structure is “beautifully simple”. It’s all in the shapes of the cells, their size, and the amount of fat in their membranes. For all its outstanding performance, the eye’s abilities were probably easy to evolve, requiring only small tweaks to the basic blueprint of the light-detecting cells.

Now that we know about the microscopic structures behind the mantis shrimp’s amazing eye, Roberts is hopeful that engineers can mimic it using liquid crystals. “The cool thing is I think it’s actually something you could make and it would improve the workings of current technologies such as Blu-Ray, which uses multiple wavelengths of light, and of future data storage devices,” he said. It wouldn’t be the first time that crustaceans have inspired technology. A new type of X-ray telescope, for example, was based on the eye of the lobster

Reference: Nature Photonics DOI: 10.1038/NPHOTON.2009.189


The amazing ways in which animals see the world


Flowers change colour and back again to advertise their opening hours

By Ed Yong | June 15, 2009 8:30 am

Blogging on Peer-Reviewed ResearchMany living things, from chameleons to fish to squid, have the ability to change their colour. But flowers? Yes, over 450 species of flower have the ability to shapeshift, altering their colour and positions over the course of a day. The goal, as with many aspects of a flower’s nature, is communication. The secondary palette tells pollinators that a particular flower has already been visited and not only needs no pollen but has little nectar to offer as a reward. The visitor’s attentions (and the pollen it carries) are directed towards needier flowers.

The legume Desmodium setigerum is one of these colour-changers. Its small flowers, just a centimetre across, last for just a day and start off with a lilac hue. When pollinating bees land on the flower, their weight “trips” one of the petals and explosively reveals the flower’s reproductive parts.

After these visits, the flowers’ top petal falls down, obscuring the anthers and stamen, and the petals transform from lilac to white and turquoise. The whole process takes less than two hours. The move to turquoise happens naturally with age but visits from bees greatly speed up the process.

But this change works both ways. Pat Willmer from the University of St Andrews has found that D.setigenrum can reverse it transformation if it hasn’t received enough pollen from its visitor. Like shopkeepers flipping their “CLOSED” signs to “OPEN”, the flowers advertise themselves as back for business by once again shifting to a lilac colour. It gives them a second chance at being pollinated.

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CATEGORIZED UNDER: Plants

The infofuse – encoding messages using colourful fire

By Ed Yong | May 26, 2009 8:30 am

Blogging on Peer-Reviewed ResearchFor many of us, the most memorable bits of school chemistry classes were lessons where we ignited metal salts over a Bunsen burner to produce brightly coloured flames, from the lilac of potassium to the distinctive red of lithium. Now a group of chemists from Harvard University have found a way of using these colourful flames to transmit coded information.

Working in the lab of legendary chemist George Whitesides, Samuel Thomas III has developed the ‘infofuse’, a strip of flammable paper patterned with metal salts. As the strip burns, the metals change the colour of the flames, creating coded pulses of light that can be used to send messages. It’s a vibrant, visual equivalent of Morse code and as a test-run, they used their infofuses to transmit the message, “LOOK MOM NO ELECTRICITY”.

Thomas sees the infofuses as the first step toward a lightweight, self-powered form of communication that doesn’t involve any electronics to store or transmit information. “We’re interested in the intersection of information and chemistry,” says Thomas, who dubs his work as ‘infochemistry’. “Cells communicate using chemical signals, and we are interested in bridging the gap between that sort of chemical communication and the digital communication that our technological infrastructure is built on.”

DNA is the biological epitome of this concept. Through a chain of molecules, it encodes instructions for building proteins that is then transmitted in the form of RNA and translated by enzymes. Outside the realm of biology, similar systems don’t exist. You could think of signal flares, smoke signals of even litmus tests as ways of transmitting information through chemistry, albeit simple and slow ones. The infofuse is more sophisticated.

It is made of a highly flammable material called nitrocellulose or ‘flash paper’. It burns with a 1,000C flame that moves along the paper at a constant speed, producing very little smoke and leaving no ash. Codes are written on the paper using small spots of metal ions dotted along the fuse strip using either a small pipette or an inkjet printer. As the strip burns, the wavelengths and order of the flames carry messages.

Infofuse.jpg

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CATEGORIZED UNDER: Technology

Are red autumn leaves a warning sign to insects?

By Ed Yong | April 15, 2009 8:30 am

Blogging on Peer-Reviewed ResearchAutumn is a time of incredible beauty, when the world becomes painted in the red, orange and yelllow palette of falling leaves. But there may be a deeper purpose to these colours, and the red ones in particular. In the eyes of some scientists, they aren’t just decay made pretty – they are a tree’s way of communicating with aphids and other insects that would make a meal of it. The message is simple: “I am strong. Don’t try it.”

During winter, trees withdraw the green chlorophyll from their leaves, and textbooks typically say that autumn colours are produced by the pigments that are left behind. That’s certainly true of yellows and oranges, but reds and purples are a different story.

They are the result of pigments called anthocyanins, which trees have to actively make. That uses up energy, which is lost to the tree when the leaf falls. An investment like that implies a purpose, and that’s what scientists have been trying to uncover.

Shortly before he died in 2000, the great William Hamilton (he of kin selection fame) suggested that autumn colours are a warning to insects. Many species, such as aphids, lay eggs in trees during autumn and their larvae feed off their host when spring arrives. That’s bad news for the tree, which defends itself with insecticidal poisons. Those that are particularly well-defended would benefit from advertising themselves as inhospitable hosts, and Hamilton suggested that they do this through red leaves.

Hamilton found some support for the idea – for example, he showed that trees that have the strongest autumn colours are also those that are plagued by the widest array of aphid pests. But his former student, Mario Archetti from the University of Oxford, has truly championed the theory and his latest findings provide the strongest support for it yet. They show that aphids avoid red-leaved apple trees, that they fare better on trees without them and that wild trees have far redder leaves than domesticated ones, which are less troubled by the challenges of insects.

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