Research Highlights

Our pick of the latest scientific literature

Evolution

When mammals picked up the evolutionary pace

Study suggests diversification was underway before demise of the dinosaurs.

Whether the rise of placental mammals occurred before or after the mass-extinction event that eliminated the dinosaurs 66 million years ago is hotly debated. Fossils found so far suggest that it happened afterwards, but ‘molecular clock’ calculations — based on the rate of genetic mutations estimated from the DNA of modern animals — indicate an earlier start time.

Shaoyuan Wu and Scott Edwards at Jiangsu Normal University in Xuzhou, China, and their colleagues ran multiple molecular analyses using genome data from 82 mammalian species. Different molecular-clock models gave highly variable timing estimates for when the placental-mammal diversification spurt started. 

But combining data from different analyses strongly suggests that the radiation started while dinosaurs were still alive, and continued steadily during and after their extinction. The radiation probably began in response to the earlier diversification of flowering plants, rather than the removal of dinosaurs, the authors say.

Materials science

Tiny antennas powered by sound

A new type of antenna can be made 100 times smaller than devices currently available.

Conventional antennas transmit when an oscillating electrical current is run through them. As a result, they cannot be significantly shorter than the wavelength of the radiation that they are designed to produce and receive.

Nian Xiang Sun at Northeastern University in Boston, Massachusetts, and his colleagues designed antennas which use a thin film that emits radio waves when set vibrating in resonance with sound waves. This is due to the coupling of magnetic and electrical properties in the material. 

Because sound waves travel much more slowly than radio waves, they have shorter wavelengths for a given frequency. So a magnetoelectric membrane for that frequency can be up to 100 times smaller than the equivalent conventional antenna, making it suitable for use in wearable electronics and nanomachines. 

The cat-sized Anatoliadelphys maasae once roamed an island that is now part of mainland Turkey.

Palaeontology

Unusually large marsupial relative unearthed in Turkey

Tree-climbing ancestor probably survived on island while placental mammals took over elsewhere.

The remains of a 44-million-year-old carnivore discovered in Turkey are forcing a rethink about the relatives of modern marsupials.

About 160 million years ago, the ancestors of modern mammals gave rise to placenta-producing eutherians and the pouch-bearing metatherians that were the forebears of modern marsupials. By the Cenozoic period, which began around 66 million years ago, it was thought that only rat-sized metatherians remained north of the equator. 

Murat Maga at the University of Washington in Seattle and Robin Beck at the University of Salford, UK, report the near-complete fossil of a new metatherian species Anatoliadelphys maasae, which is ten times larger than those animals and about the size of a modern domestic cat. It appears to have had the bone-crunching jaw strength of a Tasmanian devil (Sarcophilus harrisii) and to have been an agile tree climber. 

The part of Turkey that A. maasae roamed was an island at the time, and may have been devoid of eutherian competition, perhaps explaining this unusual metatherian persistence in the Northern Hemisphere.

The Eurasian reed warbler migrates over vast distances, from Europe to sub-Saharan Africa.

Evolution

Birds sense magnetic fields to determine longitude

Warbler’s migration is based on difference between magnetic and true north.

Migratory birds use the misalignment between Earth’s magnetic and geographic poles to gauge longitude — their position along the planet’s east–west axis.

Nikita Chernetsov at the Zoological Institute of the Russian Academy of Sciences in Rybachy and his colleagues captured Eurasian reed warblers (Acrocephalus scirpaceus, pictured) during the birds’ autumn migration from Europe to sub-Saharan Africa. 

On a clear, starry night in Rybachy, birds experienced in migration oriented themselves to take off in a southwest direction, appropriate for their usual migration. The researchers artificially rotated the magnetic field of the birds’ enclosures by 8.5° anticlockwise, making it equivalent to Earth’s magnetic field in Scotland. In response, all 15 birds changed their orientation, by an average of 151°, to face southeast, in an apparent attempt to correct for their perceived position. 

Because the stars that can act as a guide to geographic north remained unchanged, the authors conclude that warblers can sense magnetic declination — the angle between magnetic north and geographic north — and use it to determine longitude.

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Astronomy and astrophysics

Snow falls fast at night on Mars

Precipitation comes as powerful storms, not gentle drifts, on the Red Planet.

Mars has surprisingly powerful snowstorms, which form at night.

Although the planet has relatively little water vapour in its atmosphere, clouds of water-ice crystals can still develop. A team led by Aymeric Spiga of the Laboratory of Dynamic Meteorology in Paris used a high-resolution atmospheric model to study how those clouds behave over the Tharsis Montes region of Mars.

After sunset, when the air cools, water-ice clouds radiate away heat — a process that creates strong downward- and upward-flowing winds. This atmospheric churning carries water-ice particles downward, where they precipitate out as snow.

Spacecraft orbiting Mars have detected this night-time atmospheric mixing, and NASA’s Phoenix lander also spotted streaks suspected to be snow on the ground beneath a night-time cloud. The latest work ties those observations together.

Researchers had thought that snow formation on Mars was a slow and gentle process, and will now have to rethink their ideas about the Martian water cycle.

Stem cells

Extra chromosomes removed by reprogramming cells

Mice with two sex chromosomes produced from parent with three.

Cells from mice with an extra sex chromosome can be returned to normal by reprogramming them into stem cells.

Mitinori Saitou at Kyoto University in Japan, James Turner at the Francis Crick Institute in London and their colleagues took fibroblast cells from mice rendered infertile by having three sex chromosomes — either an extra X or an extra Y. They reprogrammed these fibroblasts into pluripotent stem cells, which they then converted into immature sperm cells and transplanted into mouse testes. During the reprogramming, the cells lost their extra chromosomes. The resulting sperm were able to fertilize eggs and produce baby mice with two normal sex chromosomes.

The authors say that the method could eventually be used to overcome some types of infertility in humans, and to prevent disorders, such as Down’s syndrome, that result from an abnormal number of chromosomes. 

Cancer

Virus DNA in the blood is an early sign of cancer

Spotting traces of cell-free DNA led to improved survival rates.

Searching for DNA that came from cancer cells and is circulating freely in the blood holds promise for monitoring patients with cancer, but its utility for screening asymptomatic people has been unclear.

Allen Chan and Dennis Lo at the Chinese University of Hong Kong and their colleagues screened the blood of 20,174 people with no symptoms of nasopharyngeal carcinoma, looking for traces of DNA from the Epstein–Barr virus — a biomarker for this cancer. Of 300 people who tested positive for circulating viral DNA more than once and went on to be examined, 34 had the cancer. The disease was identified at an earlier stage than is normal for this cancer, and the patients were more likely to survive. Only one person who tested negative for Epstein–Barr virus DNA developed the cancer within a year.

Researchers used the ATLAS detector, seen here under construction, to spot rare ‘light-by-light’ scattering.

Particle physics

Light seen bouncing off light at high energies for the first time

Physicists could use ‘light-by-light scattering’ to test existence of new particles.

Particles of light have been spotted scattering off each other at high energy for the first time.

Classical theories suggest that photons do not interact with each other. But the quantum theory of electromagnetism — quantum electrodynamics — predicts that two photons can interact and change direction, albeit very rarely. This has never before been seen directly at high energy. 

The ATLAS collaboration studied attempts to collide lead ions at the Large Hadron Collider (LHC) at CERN, Europe’s particle-physics laboratory near Geneva, Switzerland. When lead ions travel close to the speed of light, they radiate photons; when the ions do not themselves collide, detectors can instead spot interactions between these light particles. Of 4 billion collision attempts in 2015, the ATLAS detector saw 13 possible instances of photons interacting and scattering. 

Further LHC studies in 2018 could confirm the finding, which could be used to test the existence of new particles that are predicted to affect the interaction.

Fish exposed to food odour (right) started looking for dinner, while controls kept swimming against a current (left).

Animal behaviour

Fish fooled into thinking plastic is food

Algae-coated fragments trigger feeding response in anchovies.

Plastic fragments in the ocean quickly become covered in algae, making them smell like food to small fish. 

Tiny floating pieces of plastic waste may harm the health of sea creatures that eat them. To better understand what attracts fish to plastic particles, Matthew Savoca at the University of California, Davis, and his colleagues filmed the responses of wild-caught northern anchovies (Engraulis mordax) to the odour of plastic that had been left in the sea off California for several weeks and to their natural prey, krill (Euphausia pacifica). 

Anchovies clustered together and began searching for food in response to the smell of both krill and the biofouled plastic. But they showed no change in behaviour when presented with the smell of clean plastic or an unscented control. 

As well as showing that anchovies identify their prey by smell, the results suggest that chemical cues from a coating of algae are enough to fool the fish into believing that plastic is prey.

 

Analysis of liver tumours, among other types of cancer, is helping to link gene-expression patterns to patient survival.

Cancer

A prognostic cancer map

Cancer atlas maps gene expression to clinical outcomes.

An analysis of 17 major types of cancer using data from almost 8,000 people has yielded patterns of gene expression that can be linked to patient survival. 

Mathias Uhlen at the KTH Royal Institute of Technology in Stockholm and his colleagues mined databases of gene and protein expression from cells including liver, brain, breast and lung tumours, and compared these expression levels with those of normal cells, and with patient survival. Genes involved in DNA replication, cell division and programmed cell death tended to be expressed at higher levels in tumours than in non-cancerous cells.

The team identified a set of genes — particularly those associated with cell division and growth — whose expression level is associated with poor survival. Another set of genes linked to improved survival included those involved in regulating immune cells and in allowing cancer cells to stick to one another. 

The results are available in a public database called the Human Pathology Atlas, which contains more than 900,000 graphs comparing patient survival with the expression levels of different genes.

If it weren’t for ants, detritus would pile up in many forests.

Ecology

Ants dominate rainforest clean-up

More than half of scavenging on forest floors is done by the insects.

Ants pick up the slack when other scavengers are absent from rainforest ecosystems, despite already doing the lion’s share of such work.

Ants help to keep rainforest floors clear by taking seeds, other plant matter and even decaying carcasses back to their nests, which, in turn, creates hotspots of forest diversity. Louise Ashton at the Natural History Museum in London and her team quantified, for the first time, how much of the clean-up ants actually take on, by manipulating food availability and forager numbers in the rainforest in Sabah, Malaysia.

In a normal foraging community, ants took on 52% of the workload, leaving the rest for other insects and small vertebrates. When scavenging vertebrates were removed, ants compensated for the loss of help and took home 61% or more of the food resources. Other invertebrates did not pick up the slack in any significant way. The authors say the finding shows the importance of preventing ant decline in areas threatened by human activities.

Physics

Metal flouts Ohm’s law

Finding could provide new way to spot elusive topological effects.

The intensity of an electric current running through a metal is directly proportional to the voltage applied. This linear relationship, called Ohm’s law, is sometimes taken to be a defining characteristic of metals; the constant ratio of voltage to intensity is the electrical resistance of a given substance.

Jeehoon Kim at Pohang University of Science and Technology in South Korea and his collaborators found that, in a particular type of bismuth antimonide crystal, the electrical resistance is not constant but changes with voltage. This effect is due to a topological quirk in the energy levels of electrons that allows some of these particles to flow without resistance, and the fact that the number of such electrons varies with voltage. 

Similar deviations from Ohm’s law in other materials could be used as easier experimental signatures of such topological effects, which have tended to require expensive synchrotrons to demonstrate. 

Physics

Dark matter without the WIMPS

Theorists propose alternative route to elusive matter.

A favoured explanation for the origin of dark matter posits that the existing amount was determined in the early Universe and comes in the form of weakly interacting massive particles (WIMPs). It suggests that, in the hot, early Universe, pairs of WIMPs collided and annihilated each other, forming other particles. The reverse reaction was also taking place. This theory predicts that WIMPs should be discovered in experiments, but so far they have failed to show up.

Josh Ruderman at New York University in New York City and his colleagues propose that the crucial primordial reaction was not the annihilation, but the collision of two different types of particle. Their theory suggests that dark-matter particles would be lighter than WIMPs are thought to be. These particles would potentially be even harder to detect, but might still be observable in the cosmic microwave background and in collisions between electrons and positrons.

Fish farms, such as this one in Norway, could expand drastically to meet future demand for seafood.

Ecology

Aquaculture has plenty of room to grow

Global analysis charts ocean areas suitable for expansion of fish farming.

The total amount of seafood caught by fishermen could be equalled by farming fish in less than 0.015% of Earth’s oceans, an area smaller than Lake Michigan in the United States.

Aquaculture is increasingly important to the supply of food around the world, and many hope it can be expanded to meet the demands of a growing global population.

Rebecca Gentry at the University of California, Santa Barbara, and her colleagues modelled the ability of the world’s seas to support the farming of fish and bivalves, such as oysters and mussels. They found that both types of farming could be increased around the globe, in both tropical and temperate countries. In total, around 11.4 million square kilometres of ocean are potentially suitable for fish farming, and more than 1.5 million square kilometres for bivalves. If all suitable areas for finfish farming were used, about 15 billion tonnes of fish could be grown a year — more than 100 times current global seafood consumption. 

Small-scale gold mining often uses mercury that is then released to the environment.

Environmental sciences

Old cooking oil could be used to clean up mercury

Material can pick up pollutant from soils and water.

A type of rubber that can soak up mercury from the environment can be made cheaply from old cooking oil.

Thousands of tonnes of mercury are emitted around the world annually as a result of human activities, and put health and the environment at risk. Justin Chalker at Flinders University in Adelaide, Australia, and his colleagues created a polysulfide rubber from waste products of industrial cooking and petroleum refining. They stirred cooking oil and hot sulfur for 20 minutes at 180 °C to produce a brown solid polymer. Adding sodium chloride produced a porous, sponge-like structure that could capture mercury from water, soil and air. 

The compound can also soak up mercury that is stuck to organic matter or in the form of highly toxic alkyl-mercury compounds. The authors say that the compound could be used to clean up mercury that ends up in soil and waste water after gold mining, for example.

Genomics

Gene editing switches off pig viruses

Technique overcomes barrier to pig–human organ transplants.

The CRISPR–Cas9 gene-editing technology can be used to generate pigs that are free from viruses that could potentially infect humans.

Researchers hope that pigs might one day be able to serve as organ donors when no human organ is available. But there are concerns that viruses embedded in the pig genome could infect humans who have porcine transplants.

Luhan Yang at eGenesis in Cambridge, Massachusetts, and her colleagues injected pig cells with a CRISPR–Cas9 gene-editing system that inactivated all copies of porcine endogenous retroviruses (PERVs) from the cells. They then transferred the nuclei of these cells into pig embryos, which they implanted into sows whose genomes contained PERVs. When piglets were born, the researchers found that 100% of the PERVs in their cells had been inactivated.

The authors say that this PERV-inactivated pig strain can be a resource for researchers developing pigs with human-like organs. 

Careful incisions on remains such as these hare bones and reindeer antlers have now been found on human bone.

Archaeology

Ritualistic cannibalism in the Palaeolithic

Zigzag marks on bones found in English cave give insight into ancient traditions.

Zigzag marks on a roughly 15,000-year-old human limb bone may be the result of ritualistic cannibalism in ancient Britain.

Marks on bones found in Gough’s Cave in southwest England have previously shown that humans who lived there practised cannibalism for nutritional purposes. A team led by Silvia Bello at the Natural History Museum in London examined a human arm bone excavated from the cave in 1987. The team found evidence that humans had eaten meat from the bone: it bore incisions, human-tooth marks and damage from being pounded with a stone.

However, the radius also bore unusual zigzag marks, which are unlikely to have been created to extract flesh, the authors say. Similar patterns appear on animal bones from other European sites dated to the same period.

This type of intentional engraving has not been seen before on human bones, and suggests a previously unrecognized cannibalistic funerary practice in the Palaeolithic period.

An example of the new species — seen here on display in Argentina — is currently in a New York museum.

Palaeontology

Patagonian titan is largest dinosaur ever seen

Excavations at Argentinian ranch find remains of at least six gigantic herbivores.

A bounty of bones belonging to the largest dinosaur yet discovered has revealed a previously unknown group of prehistoric titans.

José Carballido at the Museum of Palaeontology Egidio Feruglio in Trelew, Argentina, and his colleagues analysed more than 150 bones excavated at a ranch in Patagonia. They identified at least six individuals of a new species they name Patagotitan mayorum, part of a diverse group of long-necked herbivores called titanosaurs.

The authors conclude that P. mayorum belonged to a group of particularly large titanosaurs that roamed Patagonia around 100 million years ago. The gigantism of this group probably emerged in favourable conditions created when a warmer climate took hold and the rise of flowering plants provided an abundance of food, the team suggests. P. mayorum reached almost 40 metres long and weighed up to 70 tonnes — roughly the same as 10 male African savannah elephants. 

Climate sciences

Climate patterns drove hotspot of sea-level rise on southeastern US shores

El Niño and North Atlantic Oscillation teamed up to raise coastal water levels.

Working in concert, two climate processes funnelled extra water along the south eastern coast of the United States between 2011 and 2015, exacerbating sea-level rise in the area.

Tide gauges show that, during this period, sea levels south of North Carolina’s Cape Hatteras rose by more than 20 millimetres a year — more than three times the mean global increase. A team led by Arnoldo Valle-Levinson at the University of Florida in Gainesville analysed climate patterns that could be shifting water to the region — including El Niño and the North Atlantic Oscillation.

During El Niño, changes in trade winds push more ocean water westward across the Atlantic and towards the US coast, the scientists found. And changes in the North Atlantic Oscillation, a pattern of variations in atmospheric pressure between Iceland and the Azores, drove that extra water south of Cape Hatteras to the coasts of the Carolinas and Florida. Understanding such localized ‘hotspots’ in sea-level rise could help communities better prepare for flooding.

Many different animals have been modified with CRISPR; ants have now joined their ranks.

Genetics

CRISPR ants lose ability to smell

First gene-edited mutant-ant lines show defects in social behaviour.

Two separate teams have developed the first gene-edited mutant ants, in both cases disrupting the ability to smell, and hence the ability to use pheromones to communicate.

Daniel Kronauer at the Rockefeller University in New York City and his colleagues used CRISPR gene-editing technology on the eggs of Ooceraea biroi ants, exploiting the fact that these animals reproduce through parthenogenesis to spread mutations through a colony.

Separately, Claude Desplan of New York University and his colleagues used CRISPR to modify Harpegnathos saltator eggs, making modified colonies using a feature of this species by which worker ants can become ‘pseudoqueens’ and found their own colonies.

In both cases, the ants were given mutated versions of the orco gene, which is required for odorant-receptor function. As well as showing an impaired sense of smell, both sets of mutant ants had impaired social behaviour. Both also had big reductions in an area of the brain associated with smell sensed through the antennae, suggesting that loss of odorant-receptor function can stop the development of this brain region in these animals.