Research Highlights

Our pick of the latest scientific literature

  • Volume 548
  • Issue 7668

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.

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

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

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.

New Content Item

NASA/JPL-Caltech/University Arizona/Texas A&M University

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.

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

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).

Fish exposed to food odour (right) started looking for dinner, while controls kept swimming against a current (left). M. S. Savoca et al./Proc. R. Soc. B

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.

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

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.

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

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.

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