Predatory fish use rapid color changes to coordinate attacks

Striped marlin are some of the fastest animals on the planet and one of the ocean's top predators. When hunting in groups, individual marlin will take turns attacking schools of prey fish one at a time. Now a new study reported in the journal Current Biology on February 5 helps to explain how they might coordinate this turn-taking style of attack on their prey to avoid injuring each other. The key, according to the new work, is rapid color changes.

"We documented for the first time rapid color change in a group-hunting predator, the striped marlin, as groups of marlin hunted schools of sardines," says Alicia Burns of Humboldt University in Berlin, Germany.

"We found that the attacking marlin 'lit up' and became much brighter than its group-mates as it made its attack before rapidly returning to its 'non-bright' coloration after its attack ended."

Burns and her colleagues, including Jens Krause, explained that the use of drones in their research has given them a new perspective of how marlins move and hunt.

As they examined the video footage they'd captured via drone, they noticed something unexpected: the stripes on individual marlins got obviously brighter as a fish moved in for an attack.

As they swam away, those stripes dimmed again. Were the fish changing colors to communicate with one another?

To explore this question in the new study, the researchers analyzed 12 high-resolution video clips, each containing two separate attacks on a school of sardines by two different marlin.

They also quantified the contrast of the stripes on the two attacking marlins compared to a randomly chosen marlin that wasn't attacking.

Their analysis confirms that the predatory fish rapidly change color, suggesting that the color change might serve as a reliable signal of an individual's motivation to go in for an attack.

"Color change in predators is rare, but especially so in group-hunting predators," Burns said.

"Although it is known that marlin can change color, this is the first time it's been linked to hunting or any social behavior."

The discovery suggests that marlins have more complicated communication channels than had been suspected.

The researchers propose that the color changes might even serve a dual purpose of confusing their prey.

They now hope to explore this idea, alongside other questions.

For example, they want to find out whether marlins use their color-changing abilities in other contexts.

They're curious to know whether they still change color when hunting solo and how the changes affect their prey.

They are also looking into similar color changes in other predatory species of fish.

Read more at Science Daily

New images reveal what Neptune and Uranus really look like

Neptune is fondly known for being a rich blue and Uranus green -- but a new study has revealed that the two ice giants are actually far closer in colour than typically thought.

The correct shades of the planets have been confirmed with the help of research led by Professor Patrick Irwin from the University of Oxford, which has been published today in the Monthly Notices of the Royal Astronomical Society.

He and his team found that both worlds are in fact a similar shade of greenish blue, despite the commonly-held belief that Neptune is a deep azure and Uranus has a pale cyan appearance.

Astronomers have long known that most modern images of the two planets do not accurately reflect their true colours.

The misconception arose because images captured of both planets during the 20th century -- including by NASA's Voyager 2 mission, the only spacecraft to fly past these worlds -- recorded images in separate colours.

The single-colour images were later recombined to create composite colour images, which were not always accurately balanced to achieve a "true" colour image, and -- particularly in the case of Neptune -- were often made "too blue."

In addition, the early Neptune images from Voyager 2 were strongly contrast enhanced to better reveal the clouds, bands, and winds that shape our modern perspective of Neptune.

Professor Irwin said: "Although the familiar Voyager 2 images of Uranus were published in a form closer to 'true' colour, those of Neptune were, in fact, stretched and enhanced, and therefore made artificially too blue."

"Even though the artificially-saturated colour was known at the time amongst planetary scientists -- and the images were released with captions explaining it -- that distinction had become lost over time."

"Applying our model to the original data, we have been able to reconstitute the most accurate representation yet of the colour of both Neptune and Uranus."

In the new study, the researchers used data from Hubble Space Telescope's Space Telescope Imaging Spectrograph (STIS) and the Multi Unit Spectroscopic Explorer (MUSE) on the European Southern Observatory's Very Large Telescope. In both instruments, each pixel is a continuous spectrum of colours.

This means that STIS and MUSE observations can be unambiguously processed to determine the true apparent colour of Uranus and Neptune.

The researchers used these data to re-balance the composite colour images recorded by the Voyager 2 camera, and also by the Hubble Space Telescope's Wide Field Camera 3 (WFC3).

This revealed that Uranus and Neptune are actually a rather similar shade of greenish blue. The main difference is that Neptune has a slight hint of additional blue, which the model reveals to be due to a thinner haze layer on that planet.

The study also provides an answer to the long-standing mystery of why Uranus's colour changes slightly during its 84-year orbit of the Sun.

The authors came to their conclusion after first comparing images of the ice giant to measurements of its brightness, which were recorded by the Lowell Observatory in Arizona from 1950 -- 2016 at blue and green wavelengths.

These measurements showed that Uranus appears a little greener at its solstices (i.e. summer and winter), when one of the planet's poles is pointed towards our star. But during its equinoxes -- when the Sun is over the equator -- it has a somewhat bluer tinge.

Part of the reason for this was known to be because Uranus has a highly unusual spin.

It effectively spins almost on its side during its orbit, meaning that during the planet's solstices either its north or south pole points almost directly towards the Sun and Earth.

This is important, the authors said, because any changes to the reflectivity of the polar regions would therefore have a big impact on Uranus's overall brightness when viewed from our planet.

What astronomers were less clear about is how or why this reflectivity differs.

This led the researchers to develop a model which compared the spectra of Uranus's polar regions to its equatorial regions.

It found that the polar regions are more reflective at green and red wavelengths than at blue wavelengths, partly because methane, which is red absorbing, is about half as abundant near the poles than the equator.

However, this wasn't enough to fully explain the colour change so the researchers added a new variable to the model in the form of a 'hood' of gradually thickening icy haze which has previously been observed over the summer, sunlit pole as the planet moves from equinox to solstice.

Astronomers think this is likely to be made up of methane ice particles.

When simulated in the model, the ice particles further increased the reflection at green and red wavelengths at the poles, offering an explanation as to why Uranus is greener at the solstice.

Professor Irwin said: "This is the first study to match a quantitative model to imaging data to explain why the colour of Uranus changes during its orbit."

"In this way, we have demonstrated that Uranus is greener at the solstice due to the polar regions having reduced methane abundance but also an increased thickness of brightly scattering methane ice particles."

Dr Heidi Hammel, of the Association of Universities for Research in Astronomy (AURA), who has spent decades studying Neptune and Uranus but was not involved in the study, said: "The misperception of Neptune's colour, as well as the unusual colour changes of Uranus, have bedevilled us for decades. This comprehensive study should finally put both issues to rest."

The ice giants Uranus and Neptune remain a tantalising destination for future robotic explorers, building on the legacy of Voyager in the 1980s.

Professor Leigh Fletcher, a planetary scientist from the University of Leicester and co-author of the new study, said: "A mission to explore the Uranian system -- from its bizarre seasonal atmosphere, to its diverse collection of rings and moons -- is a high priority for the space agencies in the decades to come."

However, even a long-lived planetary explorer, in orbit around Uranus, would only capture a short snapshot of a Uranian year.

Read more at Science Daily

Illusions are in the eye, not the mind

Numerous visual illusions are caused by limits in the way our eyes and visual neurones work -- rather than more complex psychological processes, new research shows.

Researchers examined illusions in which an object's surroundings affect the way we see its colour or pattern.

Scientists and philosophers have long debated whether these illusions are caused by neural processing in the eye and low-level visual centres in the brain, or involve higher-level mental processes such as context and prior knowledge.

In the new study Dr Jolyon Troscianko, from the University of Exeter, co-developed a model that suggests simple limits to neural responses -- not deeper psychological processes -- explain these illusions.

"Our eyes send messages to the brain by making neurones fire faster or slower," said Dr Troscianko, from the Centre for Ecology and Conservation on Exeter's Penryn Campus in Cornwall.

"However, there's a limit to how quickly they can fire, and previous research hasn't considered how the limit might affect the ways we see colour."

The model combines this "limited bandwidth" with information on how humans perceive patterns at different scales, together with an assumption that our vision performs best when we are looking at natural scenes.

The model was developed by researchers from the Universities of Exeter and Sussex to predict how animals see colour, but it was also found to correctly predict many visual illusions seen by humans.

"This throws into the air a lot of long-held assumptions about how visual illusions work," Dr Troscianko said.

He said the findings also shed light on the popularity of high-definition televisions.

"Modern high dynamic range televisions create bright white regions that are over 10,000 times brighter than their darkest black, approaching the contrast levels of natural scenes," Dr Troscianko added.

"How our eyes and brains can handle this contrast is a puzzle because tests show that the highest contrasts we humans can see at a single spatial scale is around 200:1.

"Even more confusingly, the neurones connecting our eyes to our brains can only handle contrasts of about 10:1.

"Our model shows how neurones with such limited contrast bandwidth can combine their signals to allow us to see these enormous contrasts, but the information is 'compressed' -- resulting in visual illusions.

"The model shows how our neurones are precisely evolved to use of every bit of capacity.

"For example, some neurones are sensitive to very tiny differences in grey levels at medium-sized scales, but are easily overwhelmed by high contrasts.

"Meanwhile, neurones coding for contrasts at larger or smaller scales are much less sensitive, but can work over a much wider range of contrasts, giving deep black-and-white differences.

"Ultimately this shows how a system with a severely limited neural bandwidth and sensitivity can perceive contrasts larger than 10,000:1."

Read more at Science Daily

Family tree of 'boring' butterflies reveals they're anything but

Walk a short distance through the Amazon Rainforest, and you might witness what look like dead leaves launch from the ground and fly off into the understory. These masters of disguise are euptychiines, one of the most diverse and least understood groups of butterflies in the American Tropics.

There are as many as 100 co-occurring euptychiine species in the rainforests of Peru and Brazil, but even the most seasoned butterfly experts have a hard time telling them apart.

"They're one of the groups that often get called 'brown, boring butterflies,'" said André Freitas, a biology professor at the State University of Campinas in Brazil. "They aren't very attractive to collectors or researchers, and even distantly related species can look very similar. The early naturalists had no way to accurately classify them."

Freitas is a co-author on a new study that adds some much-needed definition to what has remained, up until now, a black hole of butterfly diversity. The German entomologist Jacob Hübner was the first to describe the group in the early 1800s, when he lumped the few species then known into a handful genera based on similar appearance.

Using DNA, Freitas and his colleagues show there are at least 70 Euptychiina genera, containing more than 500 species. Their results also suggest there are at least 130 unnamed species in the group awaiting scientific description.

The study is the result of a project more than a decade in the making, initially conceived by Keith Willmott, director of the McGuire Center for Lepidoptera and Biodiversity at the Florida Museum of Natural History. In 2009, Willmott reached out to Freitas and other researchers who'd taken a stab at individually sorting through euptychiine butterflies piecemeal and proposed they instead combine their efforts.

Before researchers could make heads or tails of euptychiine diversity, they first needed a sense of just how many groups there were and how they were related to each other.

"The way people would typically work on this kind of problem would be to divide and conquer, but that doesn't work for euptychiines, because there are very few unifying features among species that you can use to define groups," Willmott said.

Instead, a coalition of international researchers focused on studying as many euptychiine species as they could lay their hands on. They examined more than 60,000 specimens from museums in Europe and North and South America and collected euptychiine butterflies throughout their range, from the foothills of the Andes in Ecuador to the Atlantic Forest in Southeastern Brazil.

In the process, they discovered more than 100 new species, many of which were hiding in plain sight, concealed by their close resemblance to each other.

"A recent example is a large butterfly that used to be known as Pseudodebis celia from western Ecuador, which turned out to be four separate species," Willmott said. "These are big butterflies. It's hard to imagine these kinds of species are still escaping detection."

Not all euptychiines have evolved to blend in. Several species have bright blue scales or blazing orange eyespots, which might seem like it'd make them easy to classify. But closer inspection reveals these color patterns can be deceptive as well. Results of the study's genetic analysis show, for example, that multiple, Euptychiines have transformed their wings into blue frescoes, making them appear superficially similar.

Mimicry is often the primary suspect when unrelated butterflies have a similar appearance. Predators learn to avoid species with toxic, bitter-tasting compounds, like Monarchs (Danaus plexippus). With a little false advertising, species that lack these compounds can still deter predators by copying the colors and patterns of genuinely toxic butterflies.

But according to Willmott, this likely isn't the case for euptychiines. "As far as we know, they're not unpalatable or protected against predators in any way. It looks like mimicry, but there's really no basis for it. It's a fascinating mystery that needs study."

Blue euptychiines can play further tricks on butterfly experts -- sometimes, the color is only present in some individuals of a given species.

"In most cases, the males are colorful, and the females are brown," said Marianne Espelend, a curator at the Leibniz Institute for the Analysis of Biodiversity and lead author on the study.

This mismatch has led to several cases of mistaken identity. A brown species from French Guiana described in 2012 was later determined to be the incognito female half of a well-known species discovered a century earlier. This triggered inspection of other blue species, and discovery of similar problems.

The new classification provided by this study will help researchers pin down the exact identity of familiar euptychiines and shorten the long queue of species in the group that have yet to be given a scientific name.

It also sets the stage for scientific forays into other aspects of euptychiine biology that experts are just now beginning to understand, said Freitas, reciting a litany of unknowns that can now be thoroughly investigated.

"We know that several species have scales that release scents to attract females, but we have no idea what types of chemicals are involved; the males of some species make an audible clicking sound, but we don't know how they do it; and I can count on my hand the number of times I've been able to find euptychiine caterpillars in the wild, of which we know very little."

Read more at Science Daily

Trained brains rapidly suppress visual distractions

Have you ever found yourself searching for your keys or phone only to end up getting distracted by a brightly colored object that grabs your attention? This type of attentional capture by objects that stand out from their surroundings is known as 'pop-out'. Pop-out is often functional, for instance when we want people to pay attention to bright red road signs. It can however also distract us from our goals, for instance when a brightly colored binder prevents us from finding our keys on a cluttered desk. Would it not be nice if pop-out for distracting items could somehow be blocked or suppressed to avoid distractions and help us find whatever we are looking for faster?

New research from the Vision and Cognition group at the Netherlands Institute for Neuroscience, published in PNAS, demonstrates that this is indeed possible. After training, the visual brain can suppress neuronal responses to pop-out distractors that are usually enhanced compared to responses to other, non-distracting, items. The researchers trained monkeys to play a video game in which they searched for a unique shape among multiple items, while a uniquely colored item tried to distract them. As soon as the monkeys found the unique shape, they made an eye movement to it to indicate their choice. After some training, monkeys became very good at this game and almost never made eye movements to the distractor.

Neurons in area V4 of the visual cortex, a brain area that processes visual information relatively early after is is captured by the eyes, showed consistently enhanced responses to the shape target stimuli. Responses to the distracting color stimuli on the other hand were only very briefly enhanced but became rapidly suppressed. It appears that the brain first briefly detects the presence of the distracting stimulus, and then quickly suppresses it to avoid that it will interfere with the search for the shape target. The color pop-out signal that might cause distraction is thus essentially inverted into a kind of negative pop-out, or "pop-in," to avoids distraction.

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Ethereal color variant of mysterious plant is actually a new species

Green leaves and photosynthesis were once considered essential characteristics of plants. However, some plants have stopped performing photosynthesis and take the nutrients they need from other organisms instead. One such mycoheterotrophic plant is ghostly-looking Monotropastrum humile that is widely found across East and Southeast Asia. It often grows in woodlands where there is little sunlight, obtaining the nutrients it needs by feeding off the hyphae of fungi. Despite its wide distribution, it was previously believed that only one species of this plant existed in the world. However, Professor SUETSUGU Kenji and colleagues have discovered that a variant found in Japan is actually a new species, shaking up our understanding of this unusual-looking genus of plants.

It has rosy pink petals and stems resembling milk glass, giving it a beautiful, otherworldly appearance. As it was first found around Kirishima in Kagoshima Prefecture, Japan, the new species has been named Monotropastrum kirishimense.

Originally, this new species was tentatively treated as a color variant of M. humile, known as M. humile f. roseum. Thus began an extensive and multifaceted 20-year study to determine how exactly these plants differed. Specimens were collected from throughout Japan and Taiwan, as well as Vietnam.

Results of various analyses revealed morphological differences, including the following; M. kirishimense flowers and ovaries are more rounded than those of M. humile, and its rootball is more obscured by the surrounding soil (in contrast to M. humile's protruding root tips). M. kirishimense individuals are shorter above ground (under 5cm) and longer below ground (over 10cm). The flowering season is different too; M. humile flowers bloom approximately 40 days earlier than M. kirishimense. As the two plant species have the same primary pollinator (the bumblebee Bombus diversus), this difference in flowering times can reduce heterospecific pollen deposition, helping to ensure conspecific mating, and thereby preventing them from producing hybrids.

There are several other possible reasons why M. kirishimense and M. humile may have evolved into separate species. One possibility is that they have become specialized in feeding on different fungi, which has led to reproductive isolation, or the inability to produce offspring together. This process is known as resource partitioning and is one of the major ways that species can evolve from a common ancestor. Genetic analysis of mycobionts revealed that M. kirishimense has a consistent, specialized association with a particular lineage of fungi, whereas M. humile is associated with different lineages. Therefore, this study suggests that M. kirishimense may have evolved into a new species by relying on a specific type of fungus. In fact, the phylogenetic tree (a 'family tree' of the evolutionary history of a group of organisms) of the plants themselves shows that the genetic characteristics of M. kirishimense and M. humile can be separated into two clades. Based on the researchers' analysis of various characteristics, it has been revealed that M. kirishimense is distinct from M. humile in terms of its appearance, flowering patterns, evolutionary history, and ecological relationships. Therefore, the researchers concluded that it should be recognized as an independent species.

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Picky eaters are put off by food depending on plateware color

Academics have examined the effect of colour among picky and non-picky eaters, in a first-of-its-kind study.

Previous research has demonstrated that the smell and texture of food can affect how it tastes for picky eaters, but little is known about other senses.

A team from the University of Portsmouth has discovered the colour of the bowl in which food is served also influences taste perception.

The experiment comprised nearly 50 people to measure their food neophobia, which is a reluctance to eat or try new food. The participants, who were divided into picky and non-picky eaters, then tasted the same snacks served in red, white and blue bowls.

Results revealed that both the perceived saltiness and desirability of the foods were influenced by colour in the picky group, but not the non-picky group.

Specifically, the snack was rated as higher in saltiness in the red and blue versus white bowl, and least desirable when served in the red bowl. In the UK, salty snacks are often sold in blue packaging, and the team believe that this might explain some of the saltiness findings.

Dr Lorenzo Stafford, an olfactory (sense of smell) researcher in the Department of Psychology at the University of Portsmouth, said: "Having restricted diets can lead to nutritional deficiencies as well as health problems like heart disease, poor bone health and dental issues. There is also a social cost because normally enjoyable moments between family members can easily turn into stressful, anxious, and conflict-causing situations when picky eaters feel ashamed or pressured to eat food.

"That is why it's important to understand the factors that act to 'push and pull' this behaviour."

Picky eating behaviour is usually categorised as having a limited diet, specific food preparation, strong dislikes and difficulty accepting new foods. Across a lifespan, a picky eater will generally consume fewer than 20 different food items.

The paper, published in the Food Quality and Preference journal, says this study is believed to be the first to provide insight into the interaction between colour and taste perception in adult picky and non-picky eaters and reveal a difference in the way that colour affects the perception of food in picky eaters.

It recommends further research to see if these findings extend beyond the food and colours tested here.

"This knowledge could be useful for those trying to expand the repertoire of foods," added Dr Stafford.

"For example, if you wanted to encourage a picky eater to try more vegetables well known to be viewed as bitter, you could attempt to serve them on a plate or bowl that is known to increase sweetness.

Read more at Science Daily

Bees use patterns -- not just colors -- to find flowers

Honeybees rely heavily on flower patterns -- not just colours -- when searching for food, new research shows.

A team led by the University of Exeter tested bee behaviour and built bee's-eye-view simulations to work out how they see flowers.

Honeybees have low-resolution vision (about 100 times lower than human vision), so they can only see a flower's pattern clearly when they are within few centimetres.

However, the new study shows bees can very effectively distinguish between different flowers by using a combination of colour and pattern.

In a series of tests, bees rarely ignored pattern -- suggesting colour alone does not lead them to flowers.

This may help to explain why some colours that are visible to bees are rarely produced by flowers in nature.

"We analysed a large amount of data on plants and bee behaviour," said Professor Natalie Hempel de Ibarra, from Exeter's Centre for Research in Animal Behaviour.

"By training and testing bees using artificial patterns of shape and colour, we found they relied flexibly on their ability to see both of these elements.

"Showing how insects see colour and learn colour patterns is important to understand how pollinators may, or may not, create evolutionary 'pressures' on the colours and patterns that flowers have evolved.

"Our findings suggest that flowers don't need to evolve too many different petal colours, because they can use patterns to diversify their displays so bees can tell them apart from other flowers."

One consistent feature identified in the study is that the outside edges of flowers usually contrast strongly with the plant's foliage -- while the centre of the flower does not have such a strong contrast with the foliage colour.

This could help bees quickly identify colour differences and navigate to flowers.

While flowers may be beautiful to humans, Professor Hempel de Ibarra stressed that understanding more about bees -- and the threats they face -- meant we need to see the world "through the eyes of a bee and the mind of a bee."

Read more at Science Daily

Gemini North telescope helps explain why Uranus and Neptune are different colors

Astronomers may now understand why the similar planets Uranus and Neptune are different colors. Using observations from the Gemini North telescope, the NASA Infrared Telescope Facility, and the Hubble Space Telescope, researchers have developed a single atmospheric model that matches observations of both planets. The model reveals that excess haze on Uranus builds up in the planet's stagnant, sluggish atmosphere and makes it appear a lighter tone than Neptune.

Neptune and Uranus have much in common -- they have similar masses, sizes, and atmospheric compositions -- yet their appearances are notably different. At visible wavelengths Neptune has a distinctly bluer color whereas Uranus is a pale shade of cyan. Astronomers now have an explanation for why the two planets are different colors.

New research suggests that a layer of concentrated haze that exists on both planets is thicker on Uranus than a similar layer on Neptune and 'whitens' Uranus's appearance more than Neptune's. If there were no haze in the atmospheres of Neptune and Uranus, both would appear almost equally blue.

This conclusion comes from a model that an international team led by Patrick Irwin, Professor of Planetary Physics at Oxford University, developed to describe aerosol layers in the atmospheres of Neptune and Uranus. Previous investigations of these planets' upper atmospheres had focused on the appearance of the atmosphere at only specific wavelengths. However, this new model, consisting of multiple atmospheric layers, matches observations from both planets across a wide range of wavelengths. The new model also includes haze particles within deeper layers that had previously been thought to contain only clouds of methane and hydrogen sulfide ices.

"This is the first model to simultaneously fit observations of reflected sunlight from ultraviolet to near-infrared wavelengths," explained Irwin, who is the lead author of a paper presenting this result in the Journal of Geophysical Research: Planets. "It's also the first to explain the difference in visible color between Uranus and Neptune."

The team's model consists of three layers of aerosols at different heights. The key layer that affects the colors is the middle layer, which is a layer of haze particles (referred to in the paper as the Aerosol-2 layer) that is thicker on Uranus than on Neptune. The team suspects that, on both planets, methane ice condenses onto the particles in this layer, pulling the particles deeper into the atmosphere in a shower of methane snow. Because Neptune has a more active, turbulent atmosphere than Uranus does, the team believes Neptune's atmosphere is more efficient at churning up methane particles into the haze layer and producing this snow. This removes more of the haze and keeps Neptune's haze layer thinner than it is on Uranus, meaning the blue color of Neptune looks stronger.

"We hoped that developing this model would help us understand clouds and hazes in the ice giant atmospheres," commented Mike Wong, an astronomer at the University of California, Berkeley, and a member of the team behind this result. "Explaining the difference in color between Uranus and Neptune was an unexpected bonus!"

To create this model, Irwin's team analyzed a set of observations of the planets encompassing ultraviolet, visible, and near-infrared wavelengths (from 0.3 to 2.5 micrometers) taken with the Near-Infrared Integral Field Spectrometer (NIFS) on the Gemini North telescope near the summit of Maunakea in Hawai'i -- which is part of the international Gemini Observatory, a Program of NSF's NOIRLab -- as well as archival data from the NASA Infrared Telescope Facility, also located in Hawai'i, and the NASA/ESA Hubble Space Telescope.

The NIFS instrument on Gemini North was particularly important to this result as it is able to provide spectra -- measurements of how bright an object is at different wavelengths -- for every point in its field of view. This provided the team with detailed measurements of how reflective both planets' atmospheres are across both the full disk of the planet and across a range of near-infrared wavelengths.

"The Gemini observatories continue to deliver new insights into the nature of our planetary neighbors," said Martin Still, Gemini Program Officer at the National Science Foundation. "In this experiment, Gemini North provided a component within a suite of ground- and space-based facilities critical to the detection and characterization of atmospheric hazes."

Read more at Science Daily

Pterosaur discovery solves ancient feather mystery

An international team of palaeontologists has discovered remarkable new evidence that pterosaurs, the flying relatives of dinosaurs, were able to control the colour of their feathers using melanin pigments.

The study, published in the journal Nature, was led by University College Cork (UCC) palaeontologists Dr Aude Cincotta and Prof. Maria McNamara and Dr Pascal Godefroit from the Royal Belgian Institute of Natural Sciences, with an international team of scientists from Brazil and Belgium.

The new study is based on analyses of a new 115 million year old fossilized headcrest of the pterosaur Tupandactylus imperator from north-eastern Brazil. Pterosaurs lived side by side with dinosaurs, 230 to 66 million years ago.

This species of pterosaur is famous for its bizarre huge headcrest. The team discovered that the bottom of the crest had a fuzzy rim of feathers, with short wiry hair-like feathers and fluffy branched feathers.

"We didn't expect to see this at all," said Dr Cincotta. "For decades palaeontologists have argued about whether pterosaurs had feathers. The feathers in our specimen close off that debate for good as they are very clearly branched all the way along their length, just like birds today."

The team then studied the feathers with high-powered electron microscopes and found preserved melanosomes -- granules of the pigment melanin. Unexpectedly, the new study shows that the melanosomes in different feather types have different shapes.

"In birds today, feather colour is strongly linked to melanosome shape." said Prof. McNamara. "Since the pterosaur feather types had different melanosome shapes, these animals must have had the genetic machinery to control the colours of their feathers. This feature is essential for colour patterning and shows that coloration was a critical feature of even the very earliest feathers."

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Flowers' unseen colors can help ensure pollination, survival

You can't see it, but different substances in the petals of flowers create a "bulls-eye" for pollinating insects, according to a Clemson University scientist whose research sheds light on chemical changes in flowers which helps them respond to environmental changes, including climate change, that might threaten their survival.

Matthew H. Koski, an assistant professor of biological sciences in the Clemson College of Science, led a research team that studied the bright, yellow flowers of Argentina anserina -- a member of the rose family commonly known as silverweed -- to learn how pigments in the petals that are visible only in the ultraviolet spectrum play an integral part in the plant's plasticity; that is, its ability to quickly respond to a changing environment. The team also included Clemson researchers Lindsay M. Finnell, Elizabeth Leonard and Nishanth Tharayil.

The journal Evolution featured the findings on the cover of its March edition.

The researchers studied silverweed growing at different elevations in southwestern Colorado to better understand the roles of the various UV-absorbing chemicals in the plants' petals and how these chemicals work to aid in pollination and, thus, reproduction.

Koski explained that although humans cannot see the UV patterns on the flower's petals, many of its pollinators can.

"I've always been fascinated with how [color variation of flowers] arises and how it evolves and what factors drive the evolution of color variation," Koski said, "so I got interested in thinking about how we perceive color versus how the organisms that interact more frequently with flowers perceive color."

"Insects -- pollinators, for example -- see in the ultraviolet spectrum," he continued. "So, flowers that reflect or absorb ultraviolet wavelengths give (to pollinators) the perception of different colors that we can't see. I've been fascinated with uncovering what these UV signals might be doing functionally with respect to pollination. When I thought about the trait of interest in ultraviolet absorption, it is biochemistry. It's a biochemical trait that leads to different perceptions of UV absorption and reflectance."

Koski said a wide range of plants have concentrations of UV-absorbing chemicals at the base of the flower's petals, while the tips of the petals have more UV-reflecting chemicals. He said this creates an overall "bulls-eye" effect that guides insects in their search for pollen.

The team wanted to uncover more about how the plants adapt to thrive in different environments -- in this case, a difference in altitude of 1,000 meters. They found that flowers at different altitudes adapt to their environments by producing differing amounts of UV-blocking or UV-absorbing chemicals.

"At higher elevations, there are always more UV-absorbing compounds or larger spatial area of UV absorption on the petals, compared to the low-elevation populations," Koski said.

The researchers said this demonstrates the plant's plasticity, which Koski defined as how differing traits arise in the same organisms under different environmental conditions. This is a critical step in understanding how organisms adapt to survive change.

"What's important about plasticity is, when we think about climate change and global change, plasticity is one mechanism by which natural populations can respond really rapidly to changing climates and persist under those climates," he said. "The process of evolution, where you're getting changes in the genetic code over time, is thought to proceed more slowly than just responding plastically to environmental change."

Koski said that one question raised by the research is whether plastic responses to environmental situations are adaptive. Do they offer any advantage to an organism, or are they changes in how a trait develops because of the environment without impacting plant fitness?

"One thing this study found is that the plastic change in UV pigmentation benefited the plant, especially the ones at high elevations because increases in ultraviolet absorption on the petals resulted in increased pollen viability," he explained.

Koski went on to say the research will help scientists better understand how organisms respond to environmental changes and even predict if or how well some organisms would be able to survive rapid environmental change, such as from global climate change. The research could also be important for agriculture, he said, because some of the same UV-sensitive pigments at work in silverweed are also present in commercial crops such as mustard and sunflowers.

"It's interesting to think about if abiotic factors like UV or temperature are shifting the expression of these traits, how is that going to impact how pollinators view the flowers, and how's that going to affect things like yield and seed production in crops, for example," Koski said.

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Lightweight composite material inspects itself: Changes in color indicate deformations

ETH Zurich researchers have developed a new type of laminate that changes colour as soon as the material is deformed. This way, the materials researchers can kill two birds with one stone: a lightweight composite material that inspects itself.

Lightweight construction has found its way into many areas, especially automotive manufacturing, shipbuilding and aircraft construction. In addition to traditional lightweight metals such as aluminium, magnesium or titanium, load-​bearing applications are increasingly featuring composite materials. This is driving a concurrent need to develop new techniques and methods for the early detection of damage to or even the possible failure of such as yet understudied materials.

Researchers from the Complex Materials Group at ETH Zurich, working in collaboration with researchers from the University of Fribourg, have now adopted an approach that has recently garnered attention in materials research: they have created a lightweight material that uses a colour change to indicate internal deformation and thus possible material failure at an early stage. Composed of individual layers, their laminate is translucent, break-​resistant and yet very lightweight.

Artificial mother-​of-pearl combined with polymer

The laminate is composed of alternating layers of a plastic polymer and artificial nacre or mother-​of-pearl. The latter is a speciality of the Complex Materials Laboratory and is modelled on the biological example of the mussel shell. It consists of countless glass platelets arranged in parallel, which are compacted, sintered and solidified using an polymeric resin. This makes it extremely hard and break-​resistant.

The second layer consists of a polymer to which the researchers added an indicator molecule synthesised specifically for this application at the University of Fribourg. The molecule is activated as soon as the polymer experiences stretching forces, and this changes its fluorescence. The more the material stretches and the more of these molecules are activated, the more intense the fluorescence becomes.

Fluorescence indicates overstressed parts

"We used fluorescent molecules because you can measure the increase in fluorescence very well and you don't have to rely on subjective perception," says Tommaso Magrini, lead author of the study, which was recently published in the journal ACS Applied Materials and Interfaces. The system could also have been set up to produce a colour change that would be directly perceptible from the outside. But: "The perception of colours is subjective and it is difficult to draw conclusions about changes in the material," Magrini says.

With the help of fluorescence, the researchers can now identify overstressed areas within the composite material even before fractures form. This allows early detection of vulnerable areas in a structure before catastrophic failure occurs. One possible application of the novel laminate is in components in the load-​bearing structures found in buildings, aircraft or vehicles, where it is essential to detect their failure at an early stage.

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Genetic enigma solved: Inheritance of coat color patterns in dogs

An international team of researchers including scientists from the Institute of Genetics of the University of Bern has unraveled the enigma of inheritance of coat color patterns in dogs. The researchers discovered that a genetic variant responsible for a very light coat in dogs and wolves originated more than two million years ago in a now extinct relative of the modern wolf.

The inheritance of several coat color patterns in dogs has been controversially debated for decades. Researchers including Tosso Leeb from the Institute of Genetics of the University of Bern have now finally been able to solve the puzzle. Not only did they clarify how the coat color patterns are genetically controlled, but the researchers also discovered that the light coat color in white arctic wolves and many modern dogs is due to a genetic variant originating in a species that went extinct a long time ago. The study has just been published in the scientific journal Nature Ecology and Evolution.

Two pigments and a "switch" for all coat colors

Wolves and dogs can make two different types of pigment, the black one, called eumelanin and the yellow, pheomelanin. A precisely regulated production of these two pigments at the right time and at the right place on the body gives rise to very different coat color patterns. Prior to the study, four different patterns had been recognized in dogs and several genetic variants had been theorized which cause these patterns. However, commercial genetic testing of these variants in many thousands of dogs yielded conflicting results, indicating that the existing knowledge on the inheritance of coat color patterns was incomplete and not entirely correct.

During the formation of coat color, the so-called agouti signaling protein represents the body's main switch for the production of yellow pheomelanin. If the agouti signaling protein is present, the pigment producing cells will synthesize yellow pheomelanin. If no agouti signaling protein is present, black eumelanin will be formed. "We realized early on that the causative genetic variants have to be regulatory variants which modulate the rate of protein production and lead to higher or lower amounts of agouti signal protein," Tosso Leeb explains.

Five instead of four distinct coat color patterns

The gene for agouti signaling protein has several initiation sites for reading the genetic information, which are called promoters. Dogs, on the one hand, have a ventral promoter, which is responsible for the production of agouti signaling protein at the belly. On the other hand, dogs have an additional hair cycle-specific promoter that mediates the production of agouti signaling protein during specific stages of hair growth and enables the formation of banded hair.

For the first time, the researchers characterized these two promoters in detail, in hundreds of dogs. They discovered two variants of the ventral promoter. One of the variants conveys the production of normal amounts of agouti signaling protein. The other variant has higher activity and causes the production of an increased amount of agouti signaling protein. The researchers even identified three different variants of the hair cycle-specific promoter. Starting with these variants at the individual promoters, the researchers identified a total of five different combinations, which cause different coat color patterns in dogs. "The textbooks have to be rewritten as there are five instead of the previously accepted four different patterns in dogs," Leeb says.

Unexpected insights on the evolution of wolves

As many genomes from wolves of different regions on earth have become publicly available, the researchers further investigated whether the identified genetic variants also exist in wolves. These analyses demonstrated that the variants for overactive ventral and hair cycle-specific promoters were already present in wolves prior to the domestication of modern dogs, which started approximately 40,000 years ago. Most likely, these genetic variants facilitated adaptation of wolves with a lighter coat color to snow-rich environments during past ice ages. Today, the completely white arctic wolves and the light colored wolves in the Himalaya still carry these genetic variants.

Further comparisons of the gene sequences with other species of the canidae family yielded very surprising results. The researchers were able to show that the overactive variant of the hair cycle-specific promoter in light-colored dogs and wolves shared more similarities with very distantly related species such as the golden jackal or the coyote than with the European grey wolf.

"The only plausible explanation for this unexpected finding is an ancient origin of this variant, more than two million years ago, in a now extinct relative of wolves," Leeb says. The gene segment must have been introgressed more than two million years ago into wolves by hybridization events with this now extinct relative of wolves. Thus, a small piece of DNA from this extinct species is still found today in yellow dogs and white arctic wolves. "This is reminiscent of the spectacular finding that modern humans carry a small proportion of DNA in their genomes from the now extinct Neandertals," Leeb adds.

The study was enabled by a sabbatical done by Prof. Danika Bannasch at the University of Bern with its longstanding research focus on the genetics of coat color in domestic animals. Bannasch, a professor in veterinary genetics at the University of California Davis, filtered the relevant promoter variants from thousands of other functionally neutral genetic variants. The evolutionary analyses were conducted by Christopher Kaelin and Gregory Barsh of the HudsonAlpha Institute and Stanford University.

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How we retrieve our knowledge about the world

To understand the world, we arrange individual objects, people, and events into different categories or concepts. Concepts such as 'the telephone' consist primarily of visible features, i.e. shape and color, and sounds, such as ringing. In addition, there are actions, i.e. how we use a telephone.

However, the concept of telephone does not only arise in the brain when we have a telephone in front of us. It also appears when the term is merely mentioned. If we read the word "telephone," our brain also calls up the concept of telephone. The same regions in the brain are activated that would be activated if we actually saw, heard, or used a telephone. The brain thus seems to simulate the characteristics of a telephone when its name alone is mentioned.

Until now, however, it was unclear, depending on the situation, whether the entire concept of a telephone is called up or only individual features such as sounds or actions and whether only the brain areas that process the respective feature become active. So, when we think of a telephone, do we always think of all its features or only the part that is needed at the moment? Do we retrieve our sound knowledge when a phone rings, but our action knowledge when we use it?

Researchers at the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig have now found the answer: It depends on the situation. If, for example, the study participants thought of the sounds associated with the word "telephone," the corresponding auditory areas in the cerebral cortex were activated, which are also activated during actual hearing. When thinking about using a telephone, the somatomotor areas that underlie the involved movements came into action.

In addition to these sensory-dependent, so-called modality-specific areas, it was found that there are areas that process both sounds and actions together. One of these so-called multimodal areas is the left inferior parietal lobule (IPL). It became active when both features were requested.

The researchers also found out that, in addition to characteristics based on sensory impressions and actions, there must be other criteria by which we understand and classify terms. This became apparent when the participants were only asked to distinguish between real and invented words. Here, a region that was not active for actions or sounds kicked in: the so-called anterior temporal lobe (ATL). The ATL therefore seems to process concepts abstractly or "amodally," completely detached from sensory impressions.

From these findings, the scientists finally developed a hierarchical model to reflect how conceptual knowledge is represented in the human brain. According to this model, information is passed on from one hierarchical level to the next and at the same time becomes more abstract with each step. On the lowest level, therefore, are the modality-specific areas that process individual sensory impressions or actions. These transmit their information to the multimodal regions such as the IPL, which process several linked perceptions simultaneously, such as sounds and actions. The amodal ATL, which represents features detached from sensory impressions, operates at the highest level. The more abstract a feature, the higher the level at which it is processed and the further it is removed from actual sensory impressions.

"We thus show that our concepts of things, people, and events are composed, on the one hand, of the sensory impressions and actions associated with them and, on the other hand, of abstract symbol-like features," explains Philipp Kuhnke, lead author of the study, which was published in the journal Cerebral Cortex. "Which features are activated depends strongly on the respective situation or task" added Kuhnke.

In a follow-up study in Cerebral Cortex, the researchers also found that modality-specific and multimodal regions work together in a situation-dependent manner when we retrieve conceptual features. The multimodal IPL interacted with auditory areas when retrieving sounds, and with somatomotor areas when retrieving actions. This showed that the interaction between modality-specific and multimodal regions determined the behavior of the study participants. The more these regions worked together, the more strongly the participants associated words with actions and sounds.

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Uncovering the secrets of some of the world's first color photographs

It is often said that before air travel our skies were bluer yet how, in the 21st century, could we ever know what light and colors were like one hundred years ago? Recently, a group of researchers from EPFL's Audiovisual Communications Laboratory, in the School of Computer and Communication Sciences (IC), had a unique opportunity to try to find out.

Normally hidden treasures locked away in the vaults of a handful of museums, the researchers were offered access to some of the original photographic plates and images of the scientist and inventor Gabriel Lippmann, who won the 1908 Nobel Prize in physics for his method of reproducing colors in photography.

In a paper just published in the Proceedings of the National Academy of Sciences (PNAS) the authors explain that most photographic techniques take just three measurements, for red, green and blue, however they discovered that Lippmann's historical approach typically captured 26 to 64 spectral samples of information in the visible region. His technique, based on the same interference principles that recently enabled gravitational waves to be detected and which is the foundation of holography and much of modern interferometric imaging, has been almost completely forgotten today.

"These are the earliest multi-spectral light measurements on record so we wondered whether it would be possible to accurately recreate the original light of these historical scenes," said Gilles Baechler, one of the paper's authors, "but the way the photographs were constructed was very particular so we were also really interested in whether we could create digital copies and understand how the technique worked."

The researchers found that the multi-spectral images reflected from a Lippmann plate contained distortions, although the reproduced colors looked accurate to the eye. When they examined the full spectrum reflected from a Lippmann plate, and compared it to the original, they measured a number of inconsistencies, many of which have never been documented, even in modern studies.

"We ended up modeling the full process from the multi-spectral image that you capture, all the way to recording it into the photograph. We were able to capture the light reflected back from it and measure how it differed from the original," explained Baechler. So, could the team replicate century old light?

"With the historic plates there are factors in the process that we just cannot know but because we understood how the light differed, we could create an algorithm to get back the original light that was captured. We were able to study invertibility, that is, given a spectrum produced by a Lippmann photograph we know it is possible to undo the distortions and reconstruct the original input spectrum. When we got our hands dirty and made our own plates using the historical process, we were able to verify that the modeling was correct," he continued.

While fully modeling a Nobel-prize-winning imaging technique is of significant interest in its own right, the researchers believe that revisiting Lippmann's photographic technique can inspire new technological developments this century.

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This fruit attracts birds with an unusual way of making itself metallic blue

There's a reason why blue fruits are so rare: the pigment compounds that make fruits blue are relatively uncommon in nature. But the metallic blue fruits of Viburnum tinus, a popular landscaping plant in Europe, get their color a different way. Instead of relying solely on pigments, the fruits use structural color to reflect blue light, something that's rarely seen in plants. Researchers reporting August 6 in the journal Current Biology show that the fruits use nanostructures made of lipids in their cell walls, a previously unknown mechanism of structural color, to get their striking blue -- which may also double as a signal to birds that the fruits are full of nutritious fats.

"Structural color is very common in animals, especially birds, beetles, and butterflies, but only a handful of plant species have ever been found to have structural color in their fruits," says co-first author Miranda Sinnott-Armstrong, a postdoctoral researcher at the University of Colorado-Boulder. "This means that V. tinus, in addition to showing a completely novel mechanism of structural color, is also one of the few known structurally colored fruits."

Senior author Silvia Vignolini, a physical chemist at the University of Cambridge, has been interested in the plants for nearly 10 years. "I actually found this Viburnum in a garden in Italy and observed that they looked weird, so we measured them at the time but didn't have conclusive results. It was kind of always on the back of my mind," she says. As her team grew, they become more interested in V. tinus and eventually had the capability to examine the structure of the fruits using electron microscopy. "Before we got the images, we were just seeing all these blobs," she says. "When we found out that those blobs were lipids, we got very excited."

While most plants have cell walls made of cellulose, used to make cotton and paper, V. tinus fruit cells have much thicker walls with thousands of globular lipids arranged in layers that reflect blue light. The structure formed by this so-called lipid multilayer allows the fruits to create their vibrant blue color while containing no blue pigment. "This is very strange because globular lipids like these are not usually found in this arrangement in the cell wall, as they are normally stored inside the cell and used for transport," says co-first author Rox Middleton, a physicist who studied the optical response of the fruits during her PhD and is now a postdoctoral researcher at the University of Bristol. "We also believe that this lipid may contribute to the fruit's nutrition. That means that the fruit can demonstrate how nutritious it is by being a beautiful, shiny blue."

This extra nutrition would be important for V. tinus's main consumers: birds that disperse the plant's seeds. Although the researchers can't say for sure whether the lipids are used as fat by the birds that consume them, there is reason to believe they might be. If so, the researchers suggest that the metallic blue color made by the lipid multilayer could indicate to the birds that if they see this striking blue, the fruit in question will have enough nutrients to make it a worthwhile meal. "While birds have been shown to be attracted to blue fruits," says Vignolini, "other blue fruits that we have studied essentially don't have any nutritional value."

Going forward, the researchers want to see how widespread blue structural color is in fruits to understand its ecological significance. They had never seen this type of lipid multilayer in a biomaterial before, but since their discovery, they've begun to take notice of other species. "We actually realize now that there are some older electron microscopy pictures from other plants where you can see the blobs. The researchers didn't know that they were lipids at the time, or that lipids could even form this type of structure, but our research suggests that they very well could be, meaning this structure may not be limited to Viburnum," Vignolini says.

Additionally, learning how V. tinus can use such a unique mechanism to make color may have implications for how we color our own foods. "There are lots of problems connected to food coloration," says Vignolini. She adds that once this mechanism is better understood, it could potentially be used to create a healthier, more sustainable food colorant.

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How day- and night-biting mosquitoes respond differently to colors of light and time of day

In a new study, researchers found that night- versus day-biting species of mosquitoes are behaviorally attracted and repelled by different colors of light at different times of day. Mosquitoes are among major disease vectors impacting humans and animals around the world and the findings have important implications for using light to control them.

The University of California, Irvine School of Medicine-led team studied mosquito species that bite in the daytime (Aedes aegypti, aka the Yellow Fever mosquito) and those that bite at night (Anopheles coluzzi, a member of the Anopheles gambiae family, the major vector for malaria). They found distinct responses to ultraviolet light and other colors of light between the two species. Researchers also found light preference is dependent on the mosquito's sex and species, the time of day and the color of the light.

"Conventional wisdom has been that insects are non-specifically attracted to ultraviolet light, hence the widespread use of ultraviolet light "bug zappers" for insect control. We find that day-biting mosquitoes are attracted to a wide range of light spectra during the daytime, whereas night-biting mosquitoes are strongly photophobic to short-wavelength light during the daytime," said principal investigator Todd C. Holmes, PhD, a professor in the Department of Physiology and Biophysics at the UCI School of Medicine. "Our results show that timing and light spectra are critical for species-specific light control of harmful mosquitoes."

The new study titled, "Circadian Regulation of Light-Evoked Attraction and Avoidance Behaviors in Daytime- versus Nighttime-Biting Mosquitoes," is published in Current Biology. Lisa S. Baik, a UCI School of Medicine graduate student researcher who recently completed her PhD work, is first author.

Mosquitoes pose widespread threats to humans and other animals as disease vectors. It is estimated historically that diseases spread by mosquitoes have contributed to the deaths of half of all humans ever to have lived. The new work shows that day-biting mosquitoes, particularly females that require blood meals for their fertilized eggs, are attracted to light during the day regardless of spectra. In contrast, night-biting mosquitoes specifically avoid ultraviolet (UV) and blue light during the day. Previous work in the Holmes lab using fruit flies (which are related to mosquitoes) has determined the light sensors and circadian molecular mechanisms for light mediated attraction/avoidance behaviors. Accordingly, molecular disruption of the circadian clock severely interferes with light-evoked attraction and avoidance behaviors in mosquitoes. At present, light-based insect controls do not take into consideration the day versus night behavioral profiles that change with daily light and dark cycles.

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Spectacular bird's-eye view? Hummingbirds see diverse colors humans can only imagine

Hummingbird feeding on flowers

To find food, dazzle mates, escape predators and navigate diverse terrain, birds rely on their excellent color vision.

"Humans are color-blind compared to birds and many other animals," said Mary Caswell Stoddard, an assistant professor in the Princeton University Department of Ecology and Evolutionary Biology. Humans have three types of color-sensitive cones in their eyes -- attuned to red, green and blue light -- but birds have a fourth type, sensitive to ultraviolet light. "Not only does having a fourth color cone type extend the range of bird-visible colors into the UV, it potentially allows birds to perceive combination colors like ultraviolet+green and ultraviolet+red -- but this has been hard to test," said Stoddard.

To investigate how birds perceive their colorful world, Stoddard and her research team established a new field system for exploring bird color vision in a natural setting. Working at the Rocky Mountain Biological Laboratory (RMBL) in Gothic, Colorado, the researchers trained wild broad-tailed hummingbirds (Selasphorus platycercus) to participate in color vision experiments.

"Most detailed perceptual experiments on birds are performed in the lab, but we risk missing the bigger picture of how birds really use color vision in their daily lives," Stoddard said. "Hummingbirds are perfect for studying color vision in the wild. These sugar fiends have evolved to respond to flower colors that advertise a nectar reward, so they can learn color associations rapidly and with little training."

Stoddard's team was particularly interested in "nonspectral" color combinations, which involve hues from widely separated parts of the color spectrum, as opposed to blends of neighboring colors like teal (blue-green) or yellow (green-red). For humans, purple is the clearest example of a nonspectral color. Technically, purple is not in the rainbow: it arises when our blue (short-wave) and red (long-wave) cones are stimulated, but not green (medium-wave) cones.

While humans have just one nonspectral color -- purple, birds can theoretically see up to five: purple, ultraviolet+red, ultraviolet+green, ultraviolet+yellow and ultraviolet+purple.

Stoddard and her colleagues designed a series of experiments to test whether hummingbirds can see these nonspectral colors. Their results appear June 15 in the Proceedings of the National Academy of Sciences.

The research team, which included scientists from Princeton, the University of British Columbia (UBC), Harvard University, University of Maryland and RMBL, performed outdoor experiments each summer for three years. First they built a pair of custom "bird vision" LED tubes programmed to display a broad range of colors, including nonspectral colors like ultraviolet+green. Next they performed experiments in an alpine meadow frequently visited by local broad-tailed hummingbirds, which breed at the high-altitude site.

Each morning, the researchers rose before dawn and set up two feeders: one containing sugar water and the other plain water. Beside each feeder, they placed an LED tube. The tube beside the sugar water emitted one color, while the one next to the plain water emitted a different color. The researchers periodically swapped the positions of the rewarding and unrewarding tubes, so the birds could not simply use location to pinpoint a sweet treat. They also performed control experiments to ensure that the tiny birds were not using smell or another inadvertent cue to find the reward. Over the course of several hours, wild hummingbirds learned to visit the rewarding color. Using this setup, the researchers recorded over 6,000 feeder visits in a series of 19 experiments.

The experiments revealed that hummingbirds can see a variety of nonspectral colors, including purple, ultraviolet+green, ultraviolet+red and ultraviolet+yellow. For example, hummingbirds readily distinguished ultraviolet+green from pure ultraviolet or pure green, and they discriminated between two different mixtures of ultraviolet+red light -- one redder, one less so.

"It was amazing to watch," said Harold Eyster, a UBC Ph.D. student and a co-author of the study. "The ultraviolet+green light and green light looked identical to us, but the hummingbirds kept correctly choosing the ultraviolet+green light associated with sugar water. Our experiments enabled us to get a sneak peek into what the world looks like to a hummingbird."

Even though hummingbirds can perceive nonspectral colors, appreciating how these colors appear to birds can be difficult. "It is impossible to really know how the birds perceive these colors. Is ultraviolet+red a mix of those colors, or an entirely new color? We can only speculate," said Ben Hogan, a postdoctoral research associate at Princeton and a co-author of the study.

"To imagine an extra dimension of color vision -- that is the thrill and challenge of studying how avian perception works," said Stoddard. "Fortunately, the hummingbirds reveal that they can see things we cannot."

"The colors that we see in the fields of wildflowers at our study site, the wildflower capital of Colorado, are stunning to us, but just imagine what those flowers look like to birds with that extra sensory dimension," said co-author David Inouye, who is affiliated with the University of Maryland and RMBL.

Finally, the research team analyzed a data set of 3,315 feather and plant colors. They discovered that birds likely perceive many of these colors as nonspectral, while humans do not. That said, the researchers emphasize that nonspectral colors are probably not particularly special relative to other colors. The wide variety of nonspectral colors available to birds is the result of their ancient four color-cone visual system.

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Our visual world of color is largely incorrect, study finds

Color awareness has long been a puzzle for researchers in neuroscience and psychology, who debate over how much color observers really perceive. A study from Dartmouth in collaboration with Amherst College finds that people are aware of surprisingly limited color in their peripheral vision; much of our sense of a colorful visual world is likely constructed by our brain. The findings are published in the Proceedings of the National Academy of Sciences .

To test people's visual awareness of color during naturalistic viewing, the researchers used head-mounted virtual reality displays installed with eye-trackers to immerse participants in a 360-degree real-world environment. The virtual environments included tours of historic sites, a street dance performance, a symphony rehearsal and more, where observers could explore their surroundings simply by turning their heads. With the eye-tracking tool, researchers knew exactly where an observer was looking at all times in the scene and could make systematic changes to the visual environment so that only the areas where the person was looking were in color. The rest of the scene in the periphery was desaturated so that it had no color and was just in black and white. After a series of trials, observers were asked a series of questions to gauge if they noticed the lack of color in their periphery. A supplemental video from the study illustrates how the peripheral color was removed from various scenes.

In your visual field, your periphery extends approximately 210 degrees, which is similar to if your arms are stretched out on your left and right. The study's results showed that most people's color awareness is limited to a small area around the dead center of their visual field. When the researchers removed most color in the periphery, most people did not notice. In the most extreme case, almost a third of observers did not notice when less than five percent of the entire visual field was presented in color (radius of 10 degrees visual angle).

Participants were astonished to find out later that they hadn't noticed the desaturated periphery, after they were shown the changes that were made to a virtual scene that they had just explored.

A second study tasked the participants to identify when color was desaturated in the periphery. The results were similar in that most people failed to notice when the peripheral color had been removed. A large number of people participated in the two studies, which featured nearly 180 participants in total.

"We were amazed by how oblivious participants were when color was removed from up to 95 percent of their visual world," said senior author, Caroline Robertson, an assistant professor of psychological and brain sciences at Dartmouth. "Our results show that our intuitive sense of a rich, colorful visual world is largely incorrect. Our brain is likely filling-in much of our perceptual experience."

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