Credit: 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

Neuroscience

The see-food diet of fish

How the sight of food triggers feeding behaviour in zebrafish.

A neural circuit connects the visual centre of the zebrafish brain with the region that regulates feeding. The findings suggest a way in which the sight of food can stimulate feeding behaviour.

Akira Muto and Koichi Kawakami at the National Institute of Genetics in Mishima, Japan, and their colleagues fluorescently tagged subsets of neurons in zebrafish larvae. They then imaged the animals’ transparent brains in real time as the larvae found and ate prey for the first time in their lives. The sight of food triggered activity in the brain’s feeding region in the hypothalamus. The authors pinpointed specific neurons that lit up in the visual centre at the sight of prey, and these neurons projected to the feeding area.

This circuit underlies an innate system that drives animals without any feeding experience to eat, the authors say. 

Researchers implanted an LED and engineered cells into this mouse to remotely control its insulin levels.

Researchers implanted an LED and engineered cells into this mouse to remotely control its insulin levels. Credit: Shanghai Key Laboratory of Regulatory Biology

Biotechnology

There's an app for insulin control

Smartphone-controlled engineered cells can regulate blood sugar in diabetic mice.

People with diabetes must regularly check their blood sugar levels and manually inject insulin or use other treatments. To automate the process, Haifeng Ye of East China Normal University in Shanghai and his colleagues engineered human cells to express insulin when exposed to far-red light. The team then implanted the cells into mice, along with specially designed light-emitting diodes (LEDs). A smartphone app communicated wirelessly with a home server that controlled the LEDs. When the researchers switched on the lights, the cells produced insulin. 

The authors adapted this system to regulate insulin in mice in response to blood sugar levels. A glucometer measured glucose in blood taken from the animals and sent a wireless signal to the smartphone. The system rapidly returned insulin to normal levels.

Certain proteins may have a role in allowing rainbow trout (Oncorhynchus mykiss) to sense Earth's magnetic field.

Certain proteins may have a role in allowing rainbow trout (Oncorhynchus mykiss) to sense Earth's magnetic field. Credit: Jack Perks/FLPA

Zoology

How fish sense Earth's magnetic field

Iron-binding proteins could help rainbow trout to navigate.

Many migrating animals use Earth’s magnetic field as a guide, but how they sense magnetic stimuli at the molecular level has been unclear. Cells containing iron-oxide crystals called magnetite that are sensitive to magnetic fields may be involved. To look for genes linked to magnetoreception, Robert Fitak at Duke University in Durham, North Carolina, and his colleagues exposed rainbow trout (Oncorhynchus mykiss) to a magnetic pulse and studied how gene expression in their brains changed compared with that in an unexposed control group. Fish subject to the magnetic stimulus showed increased expression of ferritin genes, which encode proteins that store iron.

The findings support the idea that ferritin proteins are involved in making or repairing magnetite-containing cells or cellular structures.

A fluorescence image of a mouse tibia, after the minerals and lipids from the bone were removed.

A fluorescence image of a mouse tibia, after the minerals and lipids from the bone were removed. Credit: Greenbaum et al./Sci. Transl. Med

Imaging

Cells spotted in see-through bone

A technique that makes bone transparent helps researchers capture images of key cells.

A technique that makes mouse bones transparent allows researchers to capture images of specific cells.

Studying bone structure often requires samples to be destroyed, and taking images of cells within opaque bone is difficult. By contrast, soft tissues such as the brain can be made transparent using various techniques. Viviana Gradinaru at the California Institute of Technology in Pasadena and her colleagues have developed a way of doing this for bone by removing minerals and lipids, allowing light to pass through while keeping the tissue intact. They used the method to visualize mouse leg bones. The team also built a microscope and software that automatically mapped and quantified bone cells that had been engineered to fluoresce. Cells were analysed up to a depth of 1.5 millimetres — more than twice the depth achieved by previous bone-imaging methods.

The technique could allow the outer layers of the brain to be studied without the skull having to be removed, the authors say.

Genomics

Wheat genome surrenders its genetic secrets

Scientists have built the most accurate wheat genome map yet, and discovered thousands of new genes.

Bread wheat (Triticum aestivum) is a staple crop in much of the world, but its large, complex genome has slowed efforts to produce a comprehensive map of the plant’s DNA. Wheat has three similar versions of its genome and more than 80% of it consists of repetitive sequences, making it difficult to piece sequenced fragments together into a full genome. Matt Clark at the Earlham Institute in Norwich, UK, and his colleagues combined next-generation sequencing technology with computer algorithms to produce the most accurate map of the wheat genome so far. The authors identified more than 100,000 genes, including nearly 23,000 that were absent or fragmented in previous wheat genome assemblies.

This map will help scientists to study differences between wheat varieties, which could aid in the breeding of improved ones, the authors say.

Climate change

Global warming ‘hiatus’ claims are overblown

The recent slowdown in warming was not a significant departure from the long-term trend of rising temperatures.

Some previous analyses of global surface-temperature data have led to claims that the long-term warming trend stalled during a 'hiatus' between 1998 and 2014. Stefan Rahmstorf at the Potsdam Institute for Climate Impact Research in Germany and his colleagues reassessed the significance of the warming slowdown, using different statistical tests from those employed by earlier studies to analyse five large data sets on global temperature. Their results confirm the period of reduced warming, but place it well within the bounds of expected natural variability.

El Niño and other short-term climate shifts could have caused this apparent slowdown in warming, but global temperatures are still rising in line with general long-term trends that began in the 1970s, the authors say.

Developmental biology

Mini-organ in a dish mimics fetal lung

A lung organoid has air sacs and branching airways.

A 3D model of the developing lung grown from human stem cells could be used to study the effects of respiratory diseases.

Previous attempts to recreate the human lung in a dish have failed to mimic the organ’s internal branching structure. Hans-Willem Snoeck at Columbia University Medical Center in New York City and his colleagues grew their lung organoid, or ‘mini-lung’, in a 3D gel matrix. After about six months, the resulting tissue resembled the lung of a second-trimester fetus, with branching airways and early versions of alveoli — the tiny air sacs in which gas exchange occurs. The ‘mini-lung’ also produced many of the same proteins as the real organ.

When researchers infected the organoids with a respiratory virus, they observed swelling and shedding of lung cells, features also seen in patients with the virus.

Holes in plastic bags containing wax moth (Galleria mellonella) caterpillars tipped off researchers that the creatures can break down plastic.

Holes in plastic bags containing wax moth (Galleria mellonella) caterpillars tipped off researchers that the creatures can break down plastic. Credit: César Hernández/CSIC

Animal behaviour

This caterpillar can digest plastic

Wax-moth larvae could inspire biotechnological methods for degrading plastic.

Researchers who were using plastic bags to carry caterpillars have discovered that one species can digest polyethylene, a ubiquitous plastic that is one of the toughest to break down.

Wax moth (Galleria mellonella) caterpillars live in beehives, feeding on honey and wax. Paolo Bombelli and Christopher Howe at the University of Cambridge, UK, and Federica Bertocchini at the University of Cantabria in Spain noticed that plastic bags holding the caterpillars quickly developed holes. To investigate, the team observed the caterpillars on polyethylene film in the laboratory, and found that about 100 of them could degrade 92 milligrams of the plastic in around 12 hours — a much higher rate than that achieved by microbes known to break down polyethylene. Homogenized caterpillar cells had the same effect, showing that the creatures are digesting the plastic, not just chewing it. 

This ability may help the caterpillars to digest beeswax, which contains compounds that are chemically similar to polyethylene. It’s not clear whether the caterpillars produce their own polyethylene-digesting enzymes or rely on gut microbes to break down the plastic, the authors say.

Optics and photonics

Scattered light reveals hidden objects

A method could be used to monitor the movement of objects invisible to radar. 

Objects obscured from view can be tracked by analysing the pattern of scattered light around the objects as they move.

Radar and laser-based tracking systems that rely on pulses of reflected light are ineffective when their targets are shrouded in fog or materials that scatter the signal from the targets. Milad Akhlaghi and Aristide Dogariu at the University of Central Florida in Orlando studied how scattered light could be used to track an object moving inside a frosted Plexiglass box. When illuminated with a laser, the box scatters the light, creating an interference pattern that changes as the object moves. By analysing these fluctuations, the team reconstructed the object’s 3D path.

Among other things, the method could be used to supplement radar to monitor aircraft hidden by fog, the authors say.

Ocean sciences

Plastic pollution drifts into Arctic cul-de-sac

An Atlantic ‘conveyor belt’ brings high levels of floating debris to the Greenland and Barents seas. 

The Arctic could be a major trap for the plastic that’s polluting the world’s oceans.

Andrés Cózar at the University of Cadiz in Spain and his colleagues took samples of floating debris while circumnavigating the Arctic Ocean. Most of the ice-free ocean was free of plastic, but the researchers found high levels of the material in the northern and eastern areas of the Greenland and Barents seas. The team estimates that 100–1,200 tonnes of plastic floats in these regions. Much of it seemed old and to have come from afar, and surface-circulation models suggest that ocean currents carried the litter to these areas from the North Atlantic.

Although the Arctic plastic amounts to less than 3% of estimated global levels, the authors suggest that much of it will eventually settle in the depths or sink to the floor of the ocean.

Microbiology

Gut bacteria could make cancer drugs work better 

Bacteria in a worm influence the activity of a common chemotherapy drug.

Differences in the gut microbiome may explain why certain cancer drugs don’t work in all patients.

Filipe Cabreiro of University College London and his colleagues fed the nematode Caenorhabditis elegans different strains of the common gut bacterium Escherichia coli, and then looked at how much of a widely used cancer drug, 5-fluorouracil, was needed to prevent the worms’ eggs from hatching. They found that different strains of E. coli had varying effects on the drug’s efficacy in hindering DNA synthesis and cell division. In the worms where only low doses of the drug were needed, the bacteria expressed key genes involved in metabolizing 5-fluorouracil into products that damage RNA or increase DNA damage in the worms.

Bacteria that express these genes in the human gut could boost drug efficacy in cancer patients.

This bryozoan, a marine invertebrate (Jellyella tuberculata), could see its skeleton dissolve in a warming climate.

This bryozoan, a marine invertebrate (Jellyella tuberculata), could see its skeleton dissolve in a warming climate. Credit: Eric Sanford/UC Davis

Climate change

Marine organism risks losing its skeleton thanks to climate change

The exoskeleton of a tiny invertebrate dissolved in acidified water in the lab.

High temperatures combined with food shortages and elevated carbon dioxide levels threaten calcified marine animals.

As the levels of atmospheric CO2 rise, the gas is partly absorbed by oceans, where it reacts to form carbonic acid. The increased acidity of the seawater can weaken marine exoskeletons. To test the effects of acidification in combination with other factors, Daniel Swezey at the University of California, Davis, and his colleagues cultivated the bryozoan Jellyella tuberculata, a tiny invertebrate that lives in honeycomb-shaped colonies in warm waters around the world. They grew the organisms in water, controlling the amount of food available, and varying the water’s temperature and level of CO2 to mimic different conditions along the California coast. They found that low temperatures coupled with high CO2 levels caused physiological stress in the organisms. Those in warm water with limited food formed skeletons with high magnesium levels that rapidly dissolved when exposed to acidic conditions. 

This is known to happen for such skeletons in acidified waters, and so bryozoans and other organisms that build such structures could be particularly vulnerable to the effects of ocean acidification, the authors suggest.

Threespine stickleback fish (Gasterosteus aculeatus) collaborate to find food.

Threespine stickleback fish (Gasterosteus aculeatus) collaborate to find food. Credit: Leo Leo/Getty

Animal behaviour

Fish pool knowledge to solve problems

Threespine sticklebacks can work together to find hidden food.

Some animals, such as ants and termites, cooperate in a variety of ways to perform tasks. To test whether partially informed individuals can pool their experiences, Mike Webster and his colleagues at the University of St Andrews, UK, challenged groups of threespine stickleback fish (Gasterosteus aculeatus) with two tasks: swimming through an environment towards a green light, and then entering a box through a small hole to find food. 

The researchers trained individual fish on just one or other of the tasks, and left some completely untrained. Next, they placed fish in groups with different combinations of experiences and counted how many in each group completed the challenge. Untrained fish with groupmates experienced in both tasks were more likely to find the food than those grouped with other untrained individuals or with fish knowledgeable in just one of the tasks.  

Fish with diverse experiences may benefit a group by helping each other to find new food sources and to avoid predators, the authors suggest.

This channel in Canada's Kaskawulsh glacier has rerouted meltwater from one river system to another one. 

This channel in Canada's Kaskawulsh glacier has rerouted meltwater from one river system to another one.  Credit: Dan Shugar

Hydrology

River piracy may rise thanks to climate change

Warm temperatures rerouted meltwater from a major Canadian glacier.

Meltwater from one of Canada’s largest glaciers has been abruptly re-routed to flow southward instead of to the north, thanks to climate change.  

The Kaskawulsh glacier in northern Canada has been retreating for more than a century, but a warm spring in 2016 caused unusually high levels of melting. Dan Shugar at the University of Washington Tacoma and his colleagues combined satellite and drone imagery with data from lake and river gauges to reconstruct the path of water flowing from the glacier. The melting in 2016 formed an ice-walled canyon, which redirected water south into the Alsek River instead of into the Slims River to the north.

This is the first evidence of rapid water rerouting in modern river systems. Such ‘river piracy’ could become more common as the climate warms, the authors warn. That would affect downstream communities and ecosystems that depend on fresh water and nutrients from the glacier.

European eels (Anguilla anguilla) can sense subtle differences in the Earth's magnetic field when migrating across the Atlantic Ocean.

European eels (Anguilla anguilla) can sense subtle differences in the Earth's magnetic field when migrating across the Atlantic Ocean. Credit: Will Meinderts/Bulten-beeld/Minden Pictures/Getty

Animal behaviour

Eels use magnetic maps to migrate

European eels navigate the 5,000-kilometre trip by sensing the Earth’s magnetic field.

Lewis Naisbett-Jones at the University of North Carolina in Chapel Hill, Nathan Putman at the University of Miami in Florida and their colleagues collected European eels (Anguilla anguilla) that had migrated from their breeding ground in the Sargasso Sea, in the western Atlantic, to the waters of the United Kingdom. When exposed to magnetic fields corresponding to regions along their migration route, the animals seemed to orient themselves in a way that would put them on course for Europe. 

The researchers modelled the migration of simulated eels, and found that virtual animals that used magnetic orientation to navigate were much more likely to reach the Gulf Stream and their final destination than those that drifted passively.

Africanized honeybees (left) are hybrids of European (right) and African ones (Apis mellifera).

Africanized honeybees (left) are hybrids of European (right) and African ones (Apis mellifera). Credit: Scott Bauer, USDA Agricultural Research Service

Evolution

‘Killer’ bee genome reveals key adaptations

Traits inherited from European ancestors could be helping Africanized bees to invade the Americas.

Africanized, or ‘killer’, bees form aggressive swarms and have largely replaced local populations across South and Central America. They emerged in Brazil in the 1960s, when introduced African honeybees bred with domestic European ones. To understand their success, a team led by Matthew Webster at Uppsala University in Sweden analysed the genomes of 32 Africanized honeybees (Apis mellifera).

The team found that most of the bees’ ancestry was African in origin, but that one long stretch of DNA was inherited from European ancestors — a sign that it was beneficial to the hybrids. Genes on this DNA segment have been linked to reproduction and foraging, and these traits might have propelled the wide spread of killer bees. 

Materials science

Porous material harvests water from dry air

A device containing the material could be used in arid regions to replenish the water supply.

A device made from a highly porous material can extract water from air with the help of sunlight.

Atmospheric water is a largely untapped source of fresh water — equivalent to about 10% of the world’s lakes — but means of collecting it are inefficient, especially in areas where humidity is low. A team led by Omar Yaghi at the University of California, Berkeley, and Evelyn Wang at the Massachusetts Institute of Technology in Cambridge developed a water-trapping device from a metal–organic framework — a material that consists of metal ions linked by organic molecules. The framework’s nanometre-sized pores adsorb water vapour. Using only sunlight, the team heated the saturated device to extract the water, which was collected by the device's condenser.

Based on the performance of a prototype, the researchers estimate that one kilogram of the material could harvest 2.8 litres of water a day at a humidity level of just 20%. The device may help to relieve water shortages in arid regions, the authors suggest.

Planetary science

Possible new dwarf planet found at the edge of the Solar System

The object is nearly three times further from the Sun than Pluto is. 

Astronomers have discovered a probable dwarf planet in the outer Solar System — the second-most-distant known object with an orbit that is well characterized.

A team led by David Gerdes at the University of Michigan in Ann Arbor found the object, 2014 UZ224 — nicknamed DeeDee — using a telescope at the Cerro Tololo Inter-American Observatory in Chile. A follow-up study using the Atacama Large Millimeter/submillimeter Array, also in Chile, measured the object’s emitted heat, which allowed the team to calculate its size. At about 635 kilometres across, 2014 UZ224 is big enough to be spherical: a key criterion for classification as a dwarf planet.

The object is currently almost three times the distance of Pluto from the Sun; the only body with a known orbit that extends farther out in the Solar System is the dwarf planet Eris.

Geysers shoot out from the surface of Enceladus, one of Saturn's moons.

Geysers shoot out from the surface of Enceladus, one of Saturn's moons. Credit: NASA/JPL/Space Science Institute

Planetary science

Hydrogen geysers on Saturn’s moon suggest the possibility of life

Chemical reactions on Enceladus are similar to those in Earth’s hydrothermal vents.

Hydrogen spraying from cracks in the surface of Enceladus hints at the presence of a buried chemical ecosystem that could support life.

Researchers reported in 2015 that Enceladus’s icy crust overlies a global ocean, which is thought to be the source of plumes seen spewing from the moon. In October 2015, NASA’s Cassini spacecraft took its deepest dive through one of the watery plumes in search of molecular hydrogen. Hunter Waite and Christopher Glein at the Southwest Research Institute in San Antonio, Texas, and their colleagues studied Cassini’s data and conclude that hydrogen probably formed from reactions driven by geothermal processes at the interface between Enceladus’s buried ocean and its rocky core. Life on Earth’s seafloor thrives on similar chemistry, even in the absence of sunlight.

Possible missions to search for life on Enceladus are under discussion.

The Ghent Altarpiece is considered to be a masterpiece of European mediaeval painting.

The Ghent Altarpiece is considered to be a masterpiece of European mediaeval painting.

Chemistry

X-ray imaging reveals original artwork

Chemical mapping is helping conservationists to restore a famous fifteenth-century painting.

In 1432, two brothers completed an extensive work of art known as the Ghent Altarpiece, which has since been damaged and repainted several times. In 2014, conservationists began to remove all of the overpaint, guided by X-ray imaging, which researchers now report showed the condition and colours of the original artwork. 

The impact of chemical analysis on art-restoration projects is often limited by the small number of data points collected from a painting. Geert Van der Snickt at the University of Antwerp in Belgium and his colleagues used X-ray fluorescence to visualize the paint, obtaining more than 16 million measurements across the altarpiece. X-ray beams caused atoms in the paint in each layer to emit fluorescent signals that revealed the paint’s chemical composition, and so its colours. The chemical maps showed where the artwork had been touched up and helped to determine whether the hidden images were in a condition worth displaying. 

Detailed chemical imaging of paintings can support more objective decision-making in art-conservation projects, the authors suggest.