Research Highlights

Our pick of the latest scientific literature

Painted image under UV light

A painting on parchment was made with luminescent inks that glow underwater. Credit: C. Chen <i>et al</i>./<i>Angew. Chem. Int. Ed</i>

Chemistry

Coppery inks paint an underwater rainbow

Inexpensive version of luminescent pigment shrugs off water.

Inks that are inexpensive to make and shine brightly under ultraviolet light could be used to manufacture colourful coatings for light-emitting diodes.

To make a brilliantly glowing ink, Hong-Bin Yao at the University of Science and Technology of China in Hefei and his team devised nanoparticles that luminesce when they crystallise, a phenomenon called aggregation-induced emission. Most materials that exhibit such behaviour are based on expensive metals, but the researchers used molecules that contain much cheaper elements — copper and iodine. The team produced inks in a wide palette of colours by adding various organic groups to the main structure.

A QR code printed using the inks was invisible until illuminated with UV light. The inks can even adhere to surfaces underwater.

As a coating on LEDs, the inks can create lights that shine in a rainbow of colours, the authors show.

A bird flees a burning forest in the aftermath of the asteroid strike

Tree-dwelling birds were killed off along with the dinosaurs when an asteroid slammed into what is now the Gulf of Mexico. Credit: Phillip M. Krzeminski

Evolution

The giant rock that wiped out tree-dwelling birds

Forests perished after an asteroid strike wrought devastation worldwide.

Although a few birds prefer life at ground level, most perch in the safety and shade of the tree tops. But no tree-dwelling birds survived the immense asteroid strike that also killed off the dinosaurs, an ecological analysis concludes.

Daniel Field at the University of Bath, UK, and his colleagues compared the lifestyles and anatomy of birds before and after the asteroid impact, which caused a mass-extinction event 66 million years ago. The team found that all the birds that lived in the trees before the die-off became extinct at around the time the huge rock hit.

Fossil pollen records suggest that the impact’s blast and the subsequent wildfires, acid rains and sunless summers destroyed forests worldwide. Tree-top birds simply couldn’t persist for 1,000 years in a treeless world carpeted with a ‘disaster flora’ of ferns.

Today’s tree-top birds developed their affinity for the forest canopy in the time since the asteroid strike, the researchers say.

A worker fumigates a classroom in Nicaragua to combat the spread of Zika

A worker fumigates a classroom to kill mosquitoes in Nicaragua, which was infiltrated by Zika virus in early 2015. Credit: Inti Ocon/AP/REX/Shutterstock

Virology

Tracing Zika’s uncharted spread

A viral family tree shows the pathogen reached Central America surprisingly early.

The Zika virus entered Central America in 2014 from Brazil and spread undetected across the region for almost a year.

The virus, which is transmitted mostly by mosquitoes of the Aedes genus, has been linked to birth defects in babies born to women infected during pregnancy. The first Zika cases diagnosed in the Americas were reported in Brazil in May 2015, and the disease was later documented elsewhere in the Americas.

To understand how the virus spread, Charles Chiu at the University of California, San Francisco, Oliver Pybus at the University of Oxford, UK, and their colleagues sequenced 61 viral genomes from infected people in Mexico and Central America. The researchers combined those genomes with nearly 300 published reference sequences to build a viral family tree.

This showed that the virus was introduced to Honduras from Brazil in summer 2014 and then spread to Guatemala, Nicaragua and southern Mexico in late 2014 to early 2015, several months earlier than previously estimated.

Two men sitting on row boats share a cigarette

A Nepali man shares his cigarette, a favour that elicited few thanks during observations made by researchers. Credit: Olivier Asselin/Alamy

Human behaviour

‘Thank you’ has little currency worldwide

Surprisingly few people express gratitude for small favours.

Scientists who eavesdropped on nearly 1,000 conversations around the world report that people who receive favours rarely say ‘thank you’.

To test that idea, Simeon Floyd at San Francisco University of Quito in Ecuador and his colleagues obtained informed consent to install cameras equipped with microphones in homes and public spaces on five continents, allowing the researchers to record conversations in eight languages.

The team recorded almost 1,000 examples of people asking for a favour — such as a request for a cigarette — and receiving it. In only 5.5% of those cases did the recipient express appreciation with either words or a gesture. Speakers of Cha’palaa, an unwritten language spoken in Ecuador, did not once express thanks in 97 exchanges that included a favour being requested and granted.

The results indicate that explicit gratitude is not a universal social currency. Instead, people help each other on the assumption that others will help them.

Oksrukiyuk Creeks in Alaska

Data from Oksrukuyik Creek in Alaska and dozens of other streams suggest that some waterways’ carbon dioxide emissions will rise as Earth warms. Credit: Ford Ballantyne IV

Ecology

Streams may skew carbon cycle as climate warms

Higher global temperatures are forecast to change photosynthesis in waterways.

Rising global temperatures could prompt some streams to release more carbon dioxide than they do now, exacerbating climate change.

As their environment warms, algae and microbes living in streams photosynthesize faster and absorb more CO2 from the air. But they also grow faster, releasing extra CO2.

To calculate the net impact of such changes, Chao Song at the University of Georgia in Athens and his colleagues monitored the temperature, dissolved oxygen level and other traits of 69 streams around the world. They then folded the data into computer models.

The models suggest that, over time, the rising rate of photosynthesis in some streams will not keep pace with plant growth, leading to a net release of CO2. If this pattern is scaled up, a 1 °C rise in global temperatures could result in a net 24% increase in carbon released from streams worldwide.

African Clawed Frog swimming underwater

The characteristic trill of male Xenopus laevis frogs is rooted in the firing patterns of particular brain cells. Credit: Heidi & Hans-Juergen Koch/Minden/Getty

Neuroscience

The brain waves that make frogs pitch perfect

A subset of neurons helped two species to evolve distinct courting trills.

Many frog species utter distinctive calls to lure mates. One group of neurons could help to explain the difference between two species.

Erik Zornik at Reed College in Portland, Oregon, and his colleagues studied the brains of two closely related species of African clawed frog: Xenopus laevis and Xenopus petersii. Males of both species emit fast trills while courting, but X. laevis produces longer, lower-pitched trills than X. petersii.

After dissecting the frogs’ brains, the researchers identified two subtypes of neuron involved in the frogs’ calls. When the scientists isolated and triggered these cells, one subtype, called ‘fast-trill neurons’, exhibited longer-lasting and slower responses in X. laevis than in X. petersii. Bathing the brains in serotonin evoked electrical activity with a pattern that resembled that seen during courtship calls. Again, the fast-trill neurons responded more slowly and for longer in X. laevis than in X. petersii.

Changes to these neurons probably contributed to the evolution of the two species’ distinctive courtship calls.

Restorer removes tape from a 16th-century drawing

A hydrogel helps to peel sticky tape off a sixteenth-century copy of a drawing by Michaelangelo. Credit: PNAS

Materials science

Sticky tape on historic artworks comes clean

Solvent nanodroplets allow safe removal of old adhesive.

Since adhesive tape became widely available in the 1930s, conservators have often used it to hold artefacts together — including some of the Dead Sea Scrolls. But within decades, the polymers in the thick fluid that provides adhesion degrade, discolour and break apart. The polymers in tape’s plastic backing may suffer the same fate.

Piero Baglioni at the University of Florence, Italy, and his co-authors describe a technique for removing tape that is less likely than ordinary solvents to damage artworks and other objects. The researchers developed a hydrogel — a polymer with a large water component — containing solvent droplets less than 20 nanometres wide. When applied to tape, the hydrogel’s solvent droplets penetrate the backing and the adhesive, facilitating their removal.

The technique could be applied not only to tape removal, but also to cleansing objects such as scientific instruments destined for space, Baglioni says.

Artist's concept of the Milky Way galaxy

The most distant stars in the Milky Way’s disk reveal that it is perhaps 10% wider than previously estimated. Credit: NASA/JPL-Caltech

Astronomy and astrophysics

The Galaxy’s full glory revealed

Effort to measure the Milky Way’s disk yields a surprise.

The Milky Way’s disk of stars is much vaster than most astronomers thought.

One of the Milky Way’s defining features is a saucer-shaped disk of stars, among which is the Sun. A number of previous studies indicated that the disk’s outermost stars lay roughly 15 kiloparsecs (nearly 50,000 light years) from the Galaxy’s centre.

Martín López-Corredoira at the Institute of Astrophysics of the Canary Islands in La Laguna, Tenerife, Spain, and his team studied the abundance of iron and other metals in distant and poorly characterized stars. The group found that many of these far-flung stars have metal contents that mark them as belonging to the disk.

The results suggest that the disk’s most distant stars lie at least 26 kiloparsecs, and possibly as many as 31 kiloparsecs, from the Galaxy’s centre. This means that the disk might stretch more than 60 kiloparsecs in diameter — roughly 20% wider than even the largest previous estimates.

Young man slides and falls on frozen lake

Ice is slippery because molecules in the surface layer are only loosely bound to each other. Credit: Getty

Physical chemistry

Why your feet slip and slide on ice

Experiments and simulations disprove an old theory.

Skaters slide across ice because they’re riding atop a layer of rolling molecules — not because the skates melt the ice as they go, as was previously thought.

Daniel Bonn at the University of Amsterdam and his collaborators measured the friction of a metal ball sliding on ice at temperatures from −100 °C to 0 °C. At the colder end of that range, friction was high. But at around −70 °C, friction began to decrease, reaching a minimum at −7 °C — the ice temperature at typical speed-skating rinks.

Molecular dynamic simulations suggested that each molecule in a microscopic layer on the ice surface forms a bond with two to three others, compared with four bonds in the bulk of the ice. As temperature warms above −70 °C, the proportion of molecules with just two bonds begins to increase. These act like a layer of rolling logs, allowing a skater — or an unlucky pedestrian — to glide along their surface.

Factory employee inspects liquid display crystal televisions

A new form of liquid crystal — a material widely used in television and laptop screens — could lead to improved electronic displays. Credit: Tomohiro Ohsumi/Bloomberg/Getty

Chemistry

A liquid crystal that could make your television screen brighter and clearer

A material with both liquid and crystalline properties could yield better electronics.

Materials called liquid crystals have the fluidity of a liquid and the ordered nature of a crystal — properties that make them useful in devices such as television screens. Now, scientists have produced a new class of liquid crystal that promises to lead to improved electronics.

To create a more versatile liquid crystal, Ivan Smalyukh at the University of Colorado Boulder and his colleagues mixed short, rod-shaped molecules with longer particles of the same shape. The long particles spontaneously aligned themselves in a single direction. The small rods also aligned themselves — but in an orientation perpendicular to the long ones. All the rods could move relative to each other, providing the structure’s signature fluidity.

The researchers’ creation is classified as a ‘biaxial’ liquid crystal because of its two perpendicular axes of alignment. Biaxial crystals are challenging to make, but have long been sought for their useful optical qualities. The device could inspire better electronic displays, the authors say.

Megaponera analis hunting termites

Termite-eating ants calculate the speediest path to sites where their prey gather. Credit: Erik Frank

Animal behaviour

Ants’ route-finding abilities put mapping software to shame

Scouts opt to save on travel time rather than distance.

Faced with uneven terrain, ants often take the fastest, rather than the shortest, route to their destination.

Erik Frank and his colleagues at the University of Würzburg in Germany cleared paths through the grass around nests of a termite-eating ant (Megaponera analis) in Côte d’Ivoire. The ants could walk nearly twice as fast on the paths as on uncleared ground.

Individual scout ants leading raiding parties of several hundred worker ants took the artificial paths on 59% of journeys to attack termites. These routes were longer in distance but demanded 35% less travel time, on average, than a hypothetical direct route through the grass. This is the first time individual scout ants have been documented making complex route calculations.

By minimizing their time outside, ants lower their exposure to attack, the authors say.

Coloured scanning electron micrograph of solon cancer cells

Some colon tumours contain two distinct populations of cells, each resistant to a key class of drugs. Credit: Dr Gopal Murti/SPL

Cancer

A double-pronged attack on colon tumours succeeds where one doesn’t

Two populations of colon-cancer cells form a seamless and deadly partnership.

Colon-cancer treatment could be improved by targeting two signalling systems in tumour cells simultaneously, studies in mice suggest.

Most colon tumours use a signalling system called NOTCH, which is associated with cancer progression. David Horst at the Ludwig Maximilians University in Munich, Germany, and his colleagues analysed 328 human colorectal tumours and found that they tend to have high levels of NOTCH activity at their centres. But cells at the tumours’ edges typically had lower NOTCH activity than central cells. On the other hand, edge cells showed higher activity of a different signalling pathway, called MAPK, which is also tied to cancer progression.

In studies of mice, drugs that block MAPK signalling caused tumour cells with high NOTCH activity to flourish. And in reverse, drugs that blocked NOTCH allowed cancer cells with high MAPK activity to thrive. Targeting both proteins slowed colon-cancer growth better than targeting either alone.

Illustration of a large oviraptorosaur incubating a ring of eggs

A type of feathered dinosaur called an oviraptorosaur broods its eggs in this artist’s rendering. Credit: Masato Hattori

Palaeontology

Why dinosaurs arranged their eggs in a doughnut shape

A 1,600-kilogram brooding parent could be a danger to developing offspring.

Massive dinosaurs built specially designed nests to avoid crushing their eggs during incubation.

All modern birds with open-topped nests sit on them to keep the developing eggs warm. To find out whether egg-laying dinosaurs were able to do the same, Kohei Tanaka of Nagoya University Museum in Japan and his colleagues studied 40 clutches of fossilized eggs laid by oviraptorosaurs, a group of feathered dinosaurs that walked on two legs.

After analysing the eggshells’ structure, the authors concluded that oviraptorosaurs, which ranged in size from 40 to 1,600 kilograms, built open nests. The largest species laid eggs with relatively thin, weak shells. But the animals apparently compensated for this fragility and the threat of their own immense weight by laying a ring of eggs around a large central opening. This might have allowed the centre of the nest to bear some or all of the brooding parent’s weight, the authors say.

Mt Halcon forest mouse

The mouse Apomys gracilirostris is one of four closely related species on Mindoro Island in the Philippines. Credit: L. R. Heaney/The Field Museum

Evolution

Worm-eating mountain mice showcase evolution in action

One species has diverged into several, despite island’s small size.

A tropical island populated by worm-eating mice is the smallest such enclave yet known where one mammal has evolved into several species.

Speciation is thought to require a large amount of space to allow animals to separate and diversify in their own niches. To test how small this space can be, Lawrence Heaney at the Field Museum of Natural History in Chicago, Illinois, and his colleagues collected tissue samples from 21 mice living on the 9,735-square-kilometre Mindoro Island in the Philippines.

When the researchers sequenced the animals’ DNA, they found that the mice belonged to four different species of the genus Apomys. Each species lives on a different mountain, and all are descended from a single common ancestor that immigrated to Mindoro 1.5 million to 2.4 million years ago.

The finding could have implications for the design of protected areas for wildlife, the researchers say.

Firefighters transport an overdose victim to a hospital

People who die after overdosing on drugs are driving a rise in the number of organs available for transplant in the United States. Credit: Scott Olson/Getty

Health care

Soaring overdose death rate fuels rise in organ transplantation

Organs from people who died of drug overdose are just as healthy as those donated by those who died of other causes.

The number of organ transplants in the United States has grown, in large part because of a rise in deaths from drug overdoses.

The death rate from drug intoxication in the United States more than tripled between 1999 and 2016 — a year in which nearly 64,000 people in the country died from substances such as prescription opioids. To determine the impact of that trend, Mandeep Mehra at Brigham and Women’s Hospital in Boston, Massachusetts, and his colleagues examined organ-transplant statistics.

The team found that from 2000 to 2016, the proportion of organs that came from donors killed by drugs rose from 1% to nearly 14%. That rise was the primary contributor to growth in the total number of US organ transplantations in the past five years.

Patients who received hearts or lungs from donors who died of overdoses were just as likely to survive the first year after transplant as patients who received organs from people who died of head injuries.

The surface of Jupiter's icy moon Europa

Jupiter’s moon Europa has an icy crust, but an analysis of spacecraft data confirms that plumes of water vapour issue from its surface. Credit: NASA/JPL-Caltech/SETI Institute

Planetary science

A geyser spurts from one of Jupiter’s icy moons

Galileo spacecraft bolsters evidence for watery plumes on Europa.

Close-up observations of Jupiter’s moon Europa confirm that a plume, probably of water vapour, rises from its surface.

Scientists had already garnered hints of such a feature from the Hubble Space Telescope, which orbits Earth. But Xianzhe Jia at the University of Michigan in Ann Arbor and his colleagues analysed observations made by the Galileo spacecraft as it swooped past Europa.

The team compared Galileo data with computer simulations of the magnetic field and charged particles around the moon. The results consistently indicate that a plume emanates from a spot on Europa’s surface close to the location suggested by Hubble.

The presence of such a plume on Europa — like those of Saturn’s moon Enceladus — implies that the moon’s icy crust hides a vast ocean. The findings will inform the planning of missions that aim to return to these moons in the 2020s and early 2030s.

A girl sneezing

Common colds are often caused by rhinoviruses — and scientists have found a way to halt their proliferation. Credit: Peter Parks/AFP/Getty

Biochemistry

A potential cure for the common cold

A designer compound stops rhinoviruses in their tracks.

A synthetic molecule blocks the proliferation of the viruses responsible for at least one-quarter of common colds.

Cold viruses called rhinoviruses hijack cells to make viral proteins and produce new infectious particles. During this process, infected cells attach a fatty acid to a viral protein called VP0, a step thought to be crucial for the assembly of new virus particles.

Roberto Solari and Edward Tate at Imperial College London, UK, and their colleagues developed a molecule — based on a compound found in the malaria parasite (Plasmodium falciparum) — that prevents this fatty-acid attachment. When the researchers added the molecule to infected cells, it blocked the assembly of new virus particles without having any toxic effects on treated cells.

Similar approaches could be used to treat rhinovirus infections that worsen respiratory diseases such as asthma and cystic fibrosis, the authors say.

Close up of a brown marmorated stink bug on a leaf

The brown marmorated stink bug, a common pest both on farms and inside homes, can be detected through trace amounts of its DNA left on plants. Credit: George Grall/National Geographic/Getty

Ecology

Stink bugs leave DNA footprints on produce

Genetic detection is much more sensitive than conventional traps.

Stink bugs leave a DNA trail that can help scientists to detect the pest’s forays into crop fields.

The brown marmorated stink bug (Halyomorpha halys) is native to Asia, but has damaged crops across North America and Europe. Rafael Valentin at Rutgers University in New Brunswick, New Jersey, and his colleagues developed a highly sensitive method for detecting the insect. The researchers gathered DNA from the surface of fruits and vegetables by sampling water used to rinse harvested crops. Any DNA was concentrated on a filter, which was then analysed for the invasive stink bug’s genetic signature.

This method allowed the authors to verify the insect’s presence at a peach orchard known to be infested. The team also used the technique to detect the bug on each of eight days of testing at a vegetable farm that was not previously known to be infested. By comparison, conventional traps at the farm caught only one brown marmorated stink bug during the same period.

The system could help farmers to track agricultural infestations more efficiently, the authors say.

A crystal of mono ammonium phosphate

A crystal of monoammonium phosphate revealed signatures of the strange phase of matter called a time crystal. Credit: Michael Marsland/Yale University

Physics

An unexpected twist in ‘crystallized’ time

Compound’s bizarre pulsing behaviour challenges convention.

A weird phase of matter called a time crystal was once thought to be theoretically impossible. But in 2017, two teams reported seeing the first hints of these objects, which pulse in patterns that repeat over time, much as the atoms in a crystal repeat in space. Now scientists have seen this behaviour in the most unexpected system so far.

Sean Barrett and his colleagues at Yale University in New Haven, Connecticut, aimed pulses of radio waves at phosphorous nuclei in an ordered crystal of monoammonium phosphate (pictured). This caused the nuclei’s spins to oscillate, in a stable way, with a frequency of half that of the pulses — the key hallmarks of a time crystal.

Previously described time crystals were thought to maintain their repeating pattern, which might otherwise break down, in part by drawing on elements of disorder in the system. However the latest set-up includes no obvious source of disorder, which challenges assumptions about how time crystals arise.

Nerve pathways around a glioblastoma in the brain

Coloured lines trace the nerve pathways around a glioblastoma (red), a highly invasive type of brain tumour. Credit: Sherbrooke Connectivity Imaging Lab/SPL

Cancer

A map for fatal brain tumour may aid cures

Guidebook provides fine-scale details that could inform work on new treatments.

A detailed atlas of the deadliest form of brain cancer promises to be a valuable tool for both diagnosis and drug development.

Glioblastoma tumours are notoriously aggressive and difficult to remove surgically. Ralph Puchalski at the Allen Institute for Brain Science in Seattle, Washington, and his colleagues examined 42 such tumours using a technique called laser microdissection. This method allowed them to isolate anatomical regions of each tumour, such as its border and clusters of living cells surrounding patches of dead tissue. The researchers then analysed RNA sequences and gene expression for each of those regions, generating a map that the team named the Ivy Glioblastoma Atlas.

The map revealed genes whose expression varies according to a cell’s location within the glioblastoma. Other teams have already used the data to study potential drug targets.