M. De Domenico et al./Phys Rev E

Information technology

How Darknet defends itself

Researchers reveal the structure of the hidden network.

The Darknet — the global network that hosts anonymous, and often illicit, online activity — is more resistant to attack than the Internet, thanks to its decentralized structure.

The Darknet routes all data through complex paths using a network of relays to conceal users’ identities. Manlio De Domenico and Alex Arenas of Rovira i Virgili University in Tarragona, Spain, analysed the network periodically between late 2013 and early 2015. They report that the Darknet is less centralized than the Internet, routing its traffic more evenly throughout the network, rather than relying on a few core ‘hubs’ (pictured, with hubs coloured). In simulations of attacks, the researchers found that this structure meant there was less disruption to traffic flow when nodes went down.

However, the Darknet’s resilience fell slightly during the study period, suggesting the network is evolving and possibly becoming centralized.

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Highlights from recent research

Climate change

Deadly heat set to rise in megacities

Many of the world’s biggest cities will experience more dangerously hot, humid days.

The extreme heatwaves that killed more than 3,000 people in India and Pakistan in 2015 could become annual events in these regions as global temperatures rise, even if warming is kept to 2 °C above preindustrial levels.

Heat becomes dangerous to people when the heat index — which accounts for humidity and provides a measure of the ‘feels-like’ temperature — exceeds 40.6 °C. Tom Matthews at Liverpool John Moores University, UK, and his colleagues used climate models to project changes in the number of days per year that this threshold would be surpassed in 44 megacities around the world. They found that as global temperatures rise, heat stress will increase at a greater rate. This means that with 1.5 °C of warming, more than 40% of the 44 cities studied will feel this stress annually — double the number of cities affected in 1979–2005. Cities projected to experience such stress for the first time include Shanghai in China and Lagos in Nigeria.

Even with some climate-change mitigation, deadly heatwaves will occur more often in many of the world’s biggest urban centres, particularly those in South Asia and Africa.

Evolution

Diet drives primate brain size

Brains may have grown bigger because of a fruit-filled diet.

Primates’ large brains may be due to the animals’ diet rather than their social behaviour, challenging a popular theory. 

Alex DeCasien and her colleagues at New York University compiled existing data on primate brain and body size, and sorted the species into four dietary categories: omnivores, leaf-eaters, fruit-eaters and those that eat both leaves and fruit. The primates that ate fruit had significantly larger brains than those that ate just leaves; and the more fruit they ate, the larger was the ratio of their brain size to their body size. The authors think this could be due to a combination of factors — one being the high nutritional content of fruit, another being cognitive adaptations that help the primates to forage for fruit. Such adaptations could allow them, for example, to extract fruit from protective skins.

The team also found no correlation between brain size and the level of social complexity. This contradicts a widely accepted theory that states that large brains evolved to help primates to manage large social networks.

NASA/JPL-Caltech/University of Arizona/University of Idaho

Geophysics

Titan’s sands get electrically charged

Static electricity could explain the odd behaviour of Titan’s dunes.

The dunes of Saturn’s largest moon, Titan, may be held together by static electricity.

Grains of sand acquire electrostatic charge as they rub against each other, but on Earth this effect is generally negligible because gravity and a high density of heavy silicate particles minimize interactions between the particles. Joshua Méndez Harper at the Georgia Institute of Technology in Atlanta and his colleagues recreated conditions on Titan (pictured), which has one-seventh the gravity of Earth and hydrocarbon-based sand. In their lab experiments, the researchers showed that these lighter grains generated electrostatic forces strong enough to clump some of the grains together.

This could explain why sand dunes at Titan’s equator appear to grow into the wind.

Getty

Biophysics

Bees’ hairs optimized for pollen collection

Honeybee grooming has now been quantified.

The spacing between honeybees’ tiny hairs allows the insects to both capture a large amount of pollen and quickly brush it off.

Honeybees (Apis mellifera) can carry up to 30% of their own weight in pollen on the surface of their bodies and use their forelegs to remove the particles. To quantify this process, David Hu at the Georgia Institute of Technology in Atlanta and his colleagues made measurements of bee hairs and high-speed films of the insects as they groomed themselves while tethered in the lab. The team found that the space between the hairs on the body is about as wide as the pollen grains that the bees typically collect, allowing the pollen to sit atop the hairs and be easily removed. The hairs on the bees’ forelegs, however, are positioned closer together, so that the pollen becomes embedded, enabling the bees to remove large amounts of pollen with each leg swipe. 

The team also found that the viscous liquid on the surface of pollen grains boosts their capacity to stick to the hairs. The findings could be used to design surfaces that are easier to clean, the authors say.

Julian Thomson

Seismology

Big earthquake shows rare complexity

The magnitude-7.8 rupture in New Zealand broke an unusually large number of faults.

A large earthquake that rocked New Zealand’s South Island in 2016 was one of the most complex ever recorded, involving the rupture of at least 12 major faults.

A team led by Ian Hamling of GNS Science in Lower Hutt, New Zealand, used field mapping, satellite observations and other measurements to analyse the magnitude-7.8 quake (pictured), which struck on 14 November. They studied the network of geological faults that allowed the rupture to spread for more than 170 kilometres during the quake. They found that many more faults ruptured, and at greater depths, than the country’s national seismic-hazard model suggested was possible. 

Officials in other parts of the world may want to reassess their local earthquake risk, the authors suggest.

Ageing

Eliminating damaged cells revitalizes old mice

A peptide makes senescent cells self-destruct. 

A newly developed molecule causes ageing cells to commit suicide, restoring some signs of health and stamina in old mice.

Damaged cells that stop dividing, called senescent cells, accumulate with age, and are thought to contribute to inflammation, tissue damage and age-related diseases. To find ways to clear these cells, Peter de Keizer at the Erasmus University Medical Center in Rotterdam, the Netherlands, and his colleagues designed a peptide that impairs binding between the proteins FOXO4 and p53 — an interaction that normally inhibits the ‘self-destruct’ signal in senescent cells. Infusions of the peptide reversed decline in kidney function in aged mice, and eliminated weight loss and liver damage caused in mice by chemotherapy drugs. In mice with a premature ageing condition, treatment with the peptide caused them to regrow fur that had been lost, and doubled how far they could run. 

The peptide seemed to have little effect on normal cells, probably because FOXO4 is scarce in non-senescent cells. The researchers are now preparing to test the safety of their molecule in humans.

Virology

Bird flu jumps into humans with one mutation

The single-letter change makes the H7N9 flu virus more versatile. 

A single-letter change in the RNA sequence of an avian influenza virus called H7N9 could explain its continuing ability to infect humans as well as birds.

H7N9 has caused illness in more than 1,000 people since early 2013, and proved fatal in about 40% of cases. Honglin Chen at the University of Hong Kong and his colleagues compared the genome sequence of the 2013 H7N9 strain, which infects people, with those of other flu strains. They found a single-letter substitution in the RNA for one of the viral proteins in the 2013 strain. This mutation boosts the virus’s ability to infect human and mouse cells, without disrupting its ability to replicate in bird cells.

This single-letter change came from another avian flu virus, H9N2, and emerged in 2000. Surveillance programmes that monitor for this sequence in avian viruses may identify those that could potentially jump into humans. 

ESA/Rosetta/NavCam

Asteroids, comets and Kuiper belt

Landslides help to cause comet tails

Sunlight triggers land surface changes on a comet.

The collapse of cliffs on comets can create plumes of gas and dust, which contribute to comets’ characteristic tails.

Such outbursts are frequent, but their cause has been unclear. Maurizio Pajola at the NASA Ames Research Center in Moffett Field, California, and his colleagues analysed images taken by high-resolution cameras on the European Space Agency’s Rosetta spacecraft as it orbited the comet 67P/Churyumov–Gerasimenko. By comparing images taken before and after an outburst on 10 July 2015 (pictured), the team traced the origin of the event to the collapse of an already fractured cliff, and a subsequent landslide. 

In a separate study, Mohamed Ramy El-Maarry at the University of Colorado, Boulder, and his colleagues used Rosetta’s instruments to map 67P’s surface over an 18-month period. They conclude that most such surface changes are caused by increased exposure to sunlight — which evaporates ice and weakens land structures — when its orbit takes it close to the Sun every 6.5 years. 

Given that these landscape changes are relatively cosmetic, the authors suggest that the landforms on comet 67P have not changed significantly since at least 1959, when it entered its current orbit.

Drug discovery

Drug stalls protein translation

The molecule acts on the cell’s ribosomes to halt the synthesis of a protein. 

The discovery of a compound that interrupts the production of a specific protein could open up a fresh path to drug discovery. 

Cells rely on complex molecular machines called ribosomes to translate the genetic code and make proteins. Robert Dullea at Pfizer Worldwide Research and Development in Cambridge, Massachusetts, Jamie Cate at the University of California, Berkeley, and their colleagues studied a compound that causes ribosomes to stall while producing the protein PCSK9, which slows the removal of cholesterol from the blood. They found that the compound temporarily stops ribosomes from synthesizing PCSK9 when they encounter a specific protein sequence, and affects the production of only a few other proteins.

Feeding the compound to rats reduced their cholesterol levels. Such ribosome-stalling compounds could be used to inhibit proteins that are difficult to target with other kinds of drugs, the authors say.

Drug discovery

CRISPR finds cancer drug synergy

A CRISPR-based method could uncover ways to kill stubborn tumours.

Certain combinations of drugs might kill drug-resistant tumours, and a method based on the CRISPR–Cas9 gene-editing system offers a way to find them.

Tumours often become resistant to individual drugs, leading clinicians to use combinations of medicines in the hope of thwarting resistance. Michael Bassik and his colleagues at Stanford University in California developed a method that systematically disables two genes at a time in cells. They used the system to knock out 21,321 pairs of potential drug targets in leukaemia cells, looking for combinations that work synergistically to kill cancer cells. 

The team found that disabling two genes called BCL2L1 and MCL1 killed drug-resistant cells. Drugs that inhibited the proteins encoded by these genes killed more leukaemia cells than each of the two medicines did individually.

Getty Images

Materials science

Graphene coating gives colourful warning

The material could indicate early signs of stress in buildings.

A material made of overlapping layers of graphene (atom-thick sheets of carbon) changes colour when varying levels of stress are applied. This could be used in structures to provide early warning of damage.

A team led by Shanglin Gao of the Leibniz Institute of Polymer Research in Dresden, Germany, designed the coating so that it changes colour more dramatically with increasing amounts of deformation. The material was placed on a glass fibre and mimics fish scales (pictured) and butterfly wings, which reflect different colours depending on the viewing angle, because of interference between light waves bouncing off the surface.

The authors say that the coating could be placed on buildings or vehicles to provide a visual indication of potential structural failure, which usually starts as tiny, invisible cracks and deformations.

Christophe Courteau/Nature Picture Library

Christophe Courteau/Nature Picture Library

Zoology

Parrots’ laughter makes other parrots play

A New Zealand bird frolics at the sound of its companions’ 'contagious' warbling.

Hearing laughter can make people laugh, and it seems that kea parrots react similarly, displaying play behaviour after hearing a particular call from fellow birds. This makes them the first non-mammals known to experience ‘contagious’ merriment.

Raoul Schwing, now at the University of Vienna, and his colleagues studied kea parrots (Nestor notabilis; pictured) in the wild in New Zealand. They played a warbling sound that is made by the birds and associated with playful behaviour for five minutes at a time. The researchers found that the animals played more often and for longer periods of time when they heard the warble than when they heard non-play kea calls, the tweets of a local robin or an artificial tone. Play stopped shortly after the sound ceased. 

The authors conclude that the call is not a courtship invitation but stimulates playful emotion.

Astronomy and astrophysics

Star dances close to black hole

A white dwarf star’s 28-minute orbit could be one of the closest ever seen around a black hole.

A white dwarf star that circles a black hole every 28 minutes may have the closest orbit of its kind ever seen in our Galaxy. 

The system, called 47 Tuc X9, is some 4.5 kiloparsecs away. It was already thought to contain two objects orbiting each other, one of them probably a black hole, but the identity of the second object was uncertain. Arash Bahramian at the University of Alberta in Edmonton and his colleagues analysed X-ray and radio observations of the system from Earth- and space-based telescopes. They discovered that the system has high oxygen levels and noted a change in X-ray brightness roughly every half an hour. The researchers inferred that a white dwarf — a dense remnant of a Sun-like star — is orbiting the black hole at a distance of about 2.5 times that between Earth and the Moon.

The black hole has probably been sucking material from the star for tens of millions of years, but the star is unlikely to be engulfed by the black hole, say the authors. 

David Penning

Animal behaviour

Kingsnakes kill with superior constriction power

The snakes can kill bigger snakes thanks to their crushing ability.

Kingsnakes have superior crushing power, allowing them to squeeze bigger snakes to death, even when these snakes are also constrictors.

David Penning at Missouri Southern State University in Joplin and Brad Moon at the University of Louisiana at Lafayette studied 182 snakes from six species, measuring the cross-sectional area of the animals’ muscles, and quantifying the pulling force the snakes use to escape predators and the pressure used to constrict prey. Muscle area and pulling force increased with size for all snakes, but the three kingsnake (Lampropeltis) species had significantly higher constriction power per unit of body weight than the three ratsnake (Pantherophis) species, which are larger constrictors preyed upon by kingsnakes (pictured, Lampropeltis getula eating a Texas ratsnake, Pantherophis obsoletus).

This strong crushing ability may result from the snakes’ distinctive posture during constriction — regularly aligned coils wrapped around the prey — that allows them to apply more pressure, the authors say.

Cancer

Fat cells make molecule that boosts breast cancer

The molecule leads to the upregulation of certain cancer genes.

A molecule made by fat cells in human breast tissue increases the growth of certain breast-cancer cells. The finding suggests a potential reason why larger breast size seems to correlate with a higher risk of cancer.

Fat cells are thought to interact with cancer cells in the breast. To learn how, Wen-Hwa Lee at China Medical University in Taiwan and his colleagues grew human breast-cancer cells along with fat cells isolated from human breast tumours that had been surgically removed. The team found that the fat cells promoted the growth of cancer cells that made a protein called MCT2. The researchers pinpointed a small molecule, β-hydroxybutyrate, that is secreted by the fat cells and is transported into tumour cells by MCT2. This molecule upregulated several cancer genes, boosting the growth of human breast-tumour cells that express MCT2.

Developmental biology

Fatty bones weaken with age

A population of cells in bones can develop into fat cells.

The build-up of fat cells in the bone marrow could explain why bones grow weaker and heal more slowly with age.

Tim Schulz at the German Institute of Human Nutrition in Potsdam-Rehbrücke and his colleagues identified a population of stem-cell-like cells in the bones of mice that gives rise to both bone and fat cells. These progenitors produced more fat cells than bone cells in older animals and in those that ate a high-fat diet, compared with younger mice and those eating a normal diet, respectively. In mice with a fractured tibia, fat-cell precursors injected near the injury site slowed the healing process. 

The researchers found that cells in the fat-cell lineage produced a protein called dipeptidyl peptidase-4 that impaired bone regeneration. These cells also inhibited the generation of stem cells in the bone marrow that give rise to blood and immune cells.

Palaeontology

Heat could lead to small mammals

Mammals shrank in size during ancient warm periods.

Mammals might respond to global warming by shrinking in size.

During a large warming event called the Palaeocene-Eocene Thermal Maximum (PETM), some 56 million years ago, mammals became smaller. To see how common this climate-driven dwarfing might have been, Abigail D’Ambrosia of the University of New Hampshire in Durham and her colleagues measured the size of fossil teeth from four common mammal species from the Bighorn Basin in Wyoming, as a proxy for body size. The fossils, including those of an ancestral horse and a rabbit-sized hoofed animal, spanned a time period that included a climate-warming event called the Eocene Thermal Maximum 2, which occurred 53 million years ago and was less hot than the PETM. The team found that the rabbit-sized animal shrank by about 15% during the later warming event. The ancient horse species decreased in size by about 14%, whereas previous research suggested that a closely related horse shrank by roughly 30% during the PETM.

The authors hypothesize that reduced size could have helped the animals to disperse heat by increasing their surface‑to-volume ratio, or could be due to dietary changes or climate-change-related drought.

S. Bengtson et al./PLoS Biol.

Evolution

Oldest plant fossils found

Multicellular plant life may be 1.6 billion years old.

The first plants lived on Earth some 400 million years earlier than the fossil record suggested.

Fossils of the earliest multicellular algae — which are closely related to the ancestors of modern plants — are rare and, until now, the most ancient specimen was around 1.2 billion years old. Stefan Bengtson at the Swedish Museum of Natural History in Stockholm and his colleagues studied  fossils from Chitrakoot in India, and found two types of multicellular colony dating back to 1.6 billion years ago. One is a thread-like form (Rafatazmia chitrakootensis, pictured), the other, lobed (Ramathallus lobatus). Using 3D X-ray microscopy, the team found that the colonies contained structures characteristic of red algae, including some that may have been used in photosynthesis. 

This discovery may mean that dates of divergence for key parts of the tree of life need to be recalibrated, the authors say.

Evolution

Viruses switch hosts to evolve

Jumping between host species may be a key part of viral evolution.

Viruses more often evolve by jumping from one host species to another than by remaining within a particular species.

Edward Holmes and his colleagues at the University of Sydney in Australia compared the evolutionary histories of 19 virus families with those of their animal or plant hosts. They found that, in almost all cases, the trees of life for the viruses had very different branching patterns compared with the trees for the viruses’ current hosts. This suggests that viruses jump between host species more often than expected. The authors report that RNA viruses — particularly the Rhabdoviridae (which include the rabies virus) and Picornaviridae — switch host species more frequently than other viruses, whereas double-stranded DNA viruses do so the least.

These findings highlight the remarkable ability of viruses to adapt to new hosts.

Energy

Sodium battery packs a punch 

Solid electrolyte gives low-cost, rechargeable batteries a boost.

A cheap, rechargeable sodium-based battery could one day deliver high power at room temperature thanks to its hybrid solid electrolyte. 

Electrolytes allow electrical charge to flow between a battery’s electrodes. Liquid electrolytes can leak and tend to react with sodium metal, an abundant, low-cost material used for electrodes in some batteries, whereas purely solid electrolytes are poor conductors at room temperature. Shufeng Song at Chongqing University in China and his colleagues developed a hybrid solid electrolyte for sodium batteries by combining solid polyethylene oxide, sodium perchlorate and silica with an ionic liquid. They tested this in a sodium-metal battery and observed high conductivity at room temperature — a step towards increased power — and high stability over 56 cycles.

The electrolyte is a promising material for safer and more efficient sodium batteries, the authors suggest.