Ice volcanoes, patches of water ice and a slew of hydrated minerals paint a picture of dwarf planet Ceres as a geologically active world — one where water has played a starring role. That’s the theme of six papers in the Sept. 2 Science that describe data collected by the Dawn spacecraft.
A 4-kilometer-high mountain dubbed Ahuna Mons, with its bowl-shaped summit and ridged flanks, has the appearance of a cryovolcano — one that erupts water instead of magma. The relatively young Oxo crater also appears to be home to splotches of frozen water. Given that ice should last only tens to hundreds of years on Ceres’ surface, the patches must be recent additions, possibly exposed by a landslide or impact with a meteorite. The surface is also slathered with a class of minerals known as phyllosilicates — silicon-bearing substances that form in the presence of water — which further support the idea that water has been present throughout Ceres’ history.
Ceres is the largest body between Mars and Jupiter. Dawn has been orbiting Ceres since March 6, 2015 (SN: 4/4/15, p. 9), studying its geology and composition to better understand the formation of rocky worlds.
Better bone scanning of fossils offers a glimpse of preteen life some 360 million years ago.
Improved radiation scanning techniques reveal accumulating growth zones in chunks of four fossil upper forelimb bones from salamander-shaped beasts called Acanthostega, scientists report online September 7 in Nature. Vertebrate bones typically show annual growth zones diminishing in size around the time of sexual maturity. But there’s no sign of that slowdown in these four individuals from East Greenland’s mass burial of Acanthostega, says study coauthor Sophie Sanchez of Uppsala University in Sweden. They were still juveniles. The bones came from tropical Greenland of the Devonian Period. Aquatic vertebrates were developing four limbs, which would serve tetrapods well when vertebrates eventually conquered land. This mass die-off doomed at least 20 individuals, presumably when a dry spell after a flood trapped them all in a big, vanishing puddle. This find makes the strongest case yet for identifying genuine youngsters among ancient tetrapods, Sanchez says. She suspects other individuals trapped could have been juveniles too.
Not many other species were found in the mass burial. So young tetrapods may have stuck together much as today’s young fish school, Sanchez speculates. The limb shape clearly indicates that the youngsters took a long time to start adding hard bone to the initial soft cartilage, she says. So these early tetrapods were at least 6-year-olds and probably 10 years old or more. For identifying stages of life, the improved technique “allows greater resolution and rigor, so in that regard it is a plus,” says Neil Shubin of the University of Chicago, who studies a fossil fish with some tetrapod-like features called Tiktaalik. There are Tiktaalik preteens, too, he notes.
What interests Nadia Fröbisch of Museum für Naturkunde in Berlin is that some of Acanthostega individuals were different sizes but had reached the same stage of bone development. She muses that they might even have been developing along different trajectories of growth, a flexibility that would be useful in a changeable environment.
Color vision may actually work like a colorized version of a black-and-white movie, a new study suggests.
Cone cells, which sense red, green or blue light, detect white more often than colors, researchers report September 14 in Science Advances. The textbook-rewriting discovery could change scientists’ thinking about how color vision works.
For decades, researchers have known that three types of cone cells in the retina are responsible for color vision. Those cone cells were thought to send “red,” “green” and “blue” signals to the brain. The brain supposedly combines the colors, much the way a color printer does, to create a rainbow-hued picture of the world (including black and white). But the new findings indicate that “the retina is doing more of the work, and it’s doing it in a more simpleminded way,” says Jay Neitz, a color vision scientist at the University of Washington in Seattle who was not involved in the study. Red and green cone cells each come in two types: One type signals “white”; another signals color, vision researcher Ramkumar Sabesan and colleagues at the University of California, Berkeley, discovered. The large number of cells that detect white (and black — the absence of white) create a high-resolution black-and-white picture of a person’s surroundings, picking out edges and fine details. Red- and green-signaling cells fill in low-resolution color information. The process works much like filling in a coloring book or adding color to a black-and-white film, says Sabesan, who is now at the University of Washington.
Sabesan and colleagues discerned this color vision strategy by stimulating about 273 individual cone cells in the eyes of two men from the lab. The technological accomplishment of stimulating single cone cells in the retina is akin to getting people to walk on the moon, says Neitz. “It is a super technological achievement. It is an amazing thing.”
Sabesan’s team first used a microscope that could peer into living human eyes to map hundreds of light-detecting cone cells in the two volunteers. In order to get a clear picture of the cells through the distortion of the lens and cornea, the researchers borrowed techniques that astronomers use to compensate for disturbances in the atmosphere. With the blur from imperfections in the eye corrected, the researchers had to precisely target individual cells to hit with the laser. Because the eye is constantly jiggling, the researchers had to determine the pattern of the eye movements to predict where cone cells would be several milliseconds in the future. Over about two years, the researchers repeatedly stimulated 273 red or green cones one by one. After a flash of laser light was delivered to the cone, the men would indicate on a keyboard what color they had seen.
Of the red cones the researchers stimulated, 119 made the men see white, while only 48 flashed red. Similarly, only 21 of the green cones tested actually signaled green, while 77 registered white. Each individual cone probably signals only white or color, the researchers say. “It’s a rather inefficient arrangement,” says Donald MacLeod, a vision scientist at the University of California, San Diego. All the cone cells are capable of detecting color, but few actually seem to do so. Cells surrounded by cones that detect a different color were more likely to send white signals, the researchers found. That finding is unexpected and runs counter to a popular idea that cones ringed by cells detecting other colors would be better at color detection, MacLeod says.
These findings could be good news for people with color blindness. The results suggest that gene therapy that adds red or green cones could work even in adults, Neitz says. Although his group gave a monkey full color vision (SN: 10/10/09, p.14), many researchers thought human brains would never be able to incorporate additional color information even though the eye could detect it. The new findings indicate the brain needs to learn only that there is one more color needed to fill in to a basically black-and-white picture, a task it should accomplish easily, Neitz says.
New experiments have re-created the genesis of Earth’s first continents.
By putting the squeeze on water and oceanic rocks under intense heat, researchers produced material that closely resembles the first continental crust, created around 4 billion years ago. The work suggests that thick slabs of oceanic crust helped build the first continents: After plate tectonics pushed the thick slabs underground, the rocks melted, transformed and then erupted to the surface to make continents, the researchers report online August 31 in Geology. This continental origin story relies on two characteristics that make Earth unlike other rocky planets in the solar system, says study coauthor Alan Hastie, a geologist at the University of Birmingham in England. Earth has both oceans and a network of shifting tectonic plates that can force sections of the planet’s exterior underground, a process known as subduction. “Without liquid oceans and without subduction from plate tectonics, you don’t get continents,” Hastie says. “The only reason I’m sitting here on land today is because of this process.”
The scenario proposed by Hastie and colleagues doesn’t necessarily require active plate tectonics to work, says geochemist Kent Condie of the New Mexico Institute of Mining and Technology in Socorro. Plate tectonics may have started hundreds of millions of years after the first continental crust formed. If thick enough, oceanic crust could have sunk deep enough on its own to create continental crust without the need for subduction, Condie says. “We shouldn’t make the assumption that we need subduction.”
Initially after Earth formed, only oceanic crust and stacks of volcanic rock coated the planet’s surface. Continental crust — which is made of less dense rock than oceanic crust and therefore rises to higher elevations — came perhaps hundreds of millions of years later. The oldest continental crust still around today, found in Greenland, dates back to about 4 billion years ago. Re-creating the formation of the earliest continental crust involves a lot of trial and error. Scientists compress bits of various rocks at high temperatures that mimic the sinking of various types of rock into the planet’s depths. The rocks transform into different minerals under the intense heat and pressure. The goal is to create rock that looks like ancient continental crust. Using this “cook and look” method, scientists have gotten a few decent matches, but never anything that perfectly replicated the first continents. Last year, Hastie and colleagues reported finding Jamaican rocks that closely resembled early continental crust, only much younger. The researchers wondered whether the nearby Caribbean Ocean Plateau was partially to blame for the odd rocks. Ocean plateaus are slabs of oceanic crust thickened by hot plumes of material that rise from Earth’s depths. This thick crust, while somewhat rare today, was probably more common billions of years ago when Earth’s interior was much hotter, Hastie says.
Using a special press, the researchers squeezed and melted small samples of water and ocean plateau rock at pressures of up to 2.2 gigapascals — equivalent to three adult African elephants stacked on a postage stamp — and at temperatures up to 1,000° Celsius. These extreme conditions imitate the fate of a chunk of ocean plateau around 30 to 45 kilometers thick forced deep underground.
The experiment transformed the water and rock into a dead ringer for the oldest known continental crust. Once created underground, the new crust would have erupted to the surface via volcanism and formed the forerunners of the modern continents, Hastie says.
New method to measure mass in space devised — A scale for measuring weight in space that does not depend upon the attraction of gravity has been devised…. In [William Thornton’s] method, the weight of the mass is determined [by] mechanically oscillating a weight in a tray. The heavier the mass, the slower the oscillation rate. The scale is tied to an electronic unit measuring the time required for five cycles of oscillation. A reference to a chart gives the mass’s weight. — Science News, October 1, 1966
UPDATE Not much has changed. The International Space Station has two spring-based contraptions for weighing in astronauts. An individual rides the Body Mass Measurement Device like a pogo stick — in four or five bounces, it calculates weight. The Space Linear Acceleration Mass Measurement Device uses springs to pull an astronaut; the acceleration reveals weight. In 2012, researchers in Europe experimented with compact computer imaging technology — developed for video games — using photos to estimate mass based on a person’s shape and size.
Dogs may look to humans for help in solving impossible tasks thanks to some genes previously linked to social disorders in people.
Beagles with particular variants in a gene associated with autism were more likely to sidle up to and make physical contact with a human stranger, researchers report September 29 in Scientific Reports.
That gene, SEZ6L, is one of five genes in a particular stretch of beagle DNA associated with sociability in the dogs, animal behaviorist Per Jensen and colleagues at Linköping University in Sweden say. Versions of four of those five genes have been linked to human social disorders such as autism, schizophrenia and aggression. “What we figure has been going on here is that there are genetic variants that tend to make dogs more sociable and these variants have been selected during domestication,” Jensen says.
But other researchers say the results are preliminary and need to be confirmed by looking at other dog breeds. Previous genetic studies of dog domestication have not implicated these genes. But, says evolutionary geneticist Bridgett vonHoldt of Princeton University, genes that influence sociability are “not an unlikely target for domestication — as humans, we would be most interested in a protodog that was interested in spending time with humans.”
Most dog studies take DNA samples from pets or village dogs and wild wolves. Jensen’s team instead studied beagles that had been raised in a lab. None of the dogs had been trained. To test sociability, the researchers gave the dogs an unsolvable problem in a room with a female human observer whom the beagles had never seen before. The puzzle was a device with three treats that the dogs could see and smell under sliding lids. One lid was sealed shut and could not be opened.
After opening two lids, the dogs “get very confident that this is not a difficult task, but then they encounter the third lid and that’s where the problem gets impossible,” Jensen says. Wolves would have kept trying to solve the problem on their own (SN: 10/17/15, p. 10). But after some futile attempts, many of the beagles looked to the human observer for help. Some dogs tried to catch her eye, glancing back and forth between the woman and the stuck lid. Other dogs made physical contact with or just tried to stay to close to the woman.
The researchers then looked for places in the dogs’ DNA where the most and least human-friendly dogs differed. A region on chromosome 26 kept popping up, indicating that genes in that region could be involved in social interactions with people. The finding is a statistical signal, but doesn’t establish what the genes might be doing to influence the dogs’ behavior, says Adam Freedman, an evolutionary geneticist at Harvard University. And since the researchers only examined the beagles, it’s not clear that the same genes would affect behavior in other dogs, he says.
The 2016 Nobel Prize in physics is awarded for discoveries of exotic states of matter known as topological phases that can help explain phenomena such as superconductivity.
The prize is shared among three researchers: David J. Thouless, of the University of Washington in Seattle, F. Duncan M. Haldane of Princeton University and J. Michael Kosterlitz of Brown University. The Royal Swedish Academy of Sciences announced the prize October 4.
At the heart of their work is topology, a branch of mathematics that describes steplike changes in a property. An object can have zero, one or two holes, for example, but not half a hole. This year’s Nobel laureates found that topological effects could explain behaviors seen in superconductors and superfluids. “Like most discoveries, you stumble onto them and you just come to realize there is something really interesting there,” Haldane said in a phone call during the announcement.
Elephants don’t wear high heels, but they certainly walk like they do.
Foot problems plague pachyderms in captivity. But it hasn’t been clear what about captivity drives these problems.
Olga Panagiotopoulou of the University of Queensland in Australia and colleagues tested walking in nearly wild elephants. The team trained five free-ranging elephants at a park in South Africa to walk over pressure-sensing platforms to map the distribution of weight on their feet. The team compared the data with similar tests of Asian elephants in a zoo in England.
Regardless of species or setting, a trend emerged: Elephants put the most pressure on the outside toes of their front feet and the least pressure on their heels, the team reports October 5 in Royal Society Open Science. Thus, elephants naturally walk on their tiptoes. The harder surfaces of captive environments must cramp a natural walking style, the researchers conclude.
Accidental chair squeaks in a lab have tipped off researchers to a new world of eavesdroppers.
Spiders don’t have eardrums, though their exquisitely sensitive leg hairs pick up vibrations humming through solids like web silk and leaves. Biologists thought that any airborne sounds more than a few centimeters away would be inaudible. But the first recordings of auditory nerve cells firing inside a spider brain suggest that the tiny Phidippus audax jumping spider can pick up airborne sounds from at least three meters away, says Ronald Hoy of Cornell University. During early sessions of brain recordings, Hoy’s colleagues saw bursts of nerve cell, or neuron, activity when a chair moved. Systematic experiments then showed that from several meters away, spiders were able to detect relatively quiet tones at levels comparable to human conversation. In a hearing test based on behavior, the spiders also clearly noticed when researchers broadcast a low droning like the wing sound of an approaching predatory wasp. In an instant, the spiders hunkered down motionless, the researchers report online October 13 in Current Biology.
Jumping spiders have brains about the size of a poppy seed, and Hoy credits the success of probing even tinier spots inside these (anesthetized) brains to Cornell coauthor Gil Menda and his rock-steady hands. “I close my eyes,” Menda says. He listens his way along, one slight nudge of the probe at a time toward the auditory regions, as the probe monitor’s faint popping sounds grow louder. When Menda first realized the spider brain reacted to a chair squeak, he and Paul Shamble, a study coauthor now at Harvard University, started clapping hands, backing away from the spider and clapping again. The claps didn’t seem earthshaking, but the spider’s brain registered clapping even when they had backed out into the hallway, laughing with surprise. Clapping or other test sounds in theory might confound the experiment by sending vibrations not just through the air but through equipment holding the spider. So the researchers did their Cornell neuron observations on a table protected from vibrations. They even took the setup for the scary wasp trials on a trip to the lab of coauthor Ronald Miles at State University of New York at Binghamton. There, they could conduct vibration testing in a highly controlled, echo-dampened chamber. Soundwise, Hoy says, “it’s really eerie.”
Neuron tests in the hushed chamber and at Cornell revealed a relatively narrow, low-pitched range of sensitivity for these spiders, Hoy says. That lets the spiders pick up rumbly tones pitched around 70 to 200 hertz; in comparison, he says, people hear best between 500 and 1,000 Hz and can detect tones from 50 Hz to 15 kilohertz. Spiders may hear low rumbles much as they do web vibes: with specialized leg hairs, Hoy and his colleagues propose. They found that making a hair twitch could cause a sound-responsive neuron to fire. “There seems to be no physical reason why a hair could not listen,” says Jérôme Casas of the University of Tours in France. When monitoring nerve response from hairs on cricket legs, he’s tracked airplanes flying overhead. Hoy’s team calculates that an 80 Hz tone the spiders responded to would cause air velocities of only 0.13 millimeters a second if broadcast at 65 decibels three meters away. That’s hardly a sigh of a breeze. Yet it’s above the threshold for leg hair response, says Friedrich Barth of the University of Vienna, who studies spider senses.
An evolutionary pressure favoring such sensitivity might have been eons of attacks from wasps, such as those that carry off jumping spiders and immobilize them with venom, Hoy says. A mother wasp then tucks an inert, still-alive spider into each cell of her nest where a wasp egg will eventually hatch to feed on fresh spider flesh. Wasps are major predators of many kinds of spiders, says Ximena Nelson of the University of Canterbury in Christchurch, New Zealand. If detecting their wing drone turns out to have been important in the evolution of hearing, other spiders might do long-distance eavesdropping, too.
VANCOUVER — Zika virus’s tricks for interfering with human brain cell development may also be the virus’s undoing.
Zika infection interferes with DNA replication and repair machinery and also prevents production of some proteins needed for proper brain growth, geneticist Feiran Zhang of Emory University in Atlanta reported October 19 at the annual meeting of the American Society of Human Genetics.
Levels of a protein called p53, which helps control cell growth and death, shot up by 80 percent in human brain cells infected with the Asian Zika virus strain responsible for the Zika epidemic in the Americas, Zhang said. The lab dish results are also reported in the Oct. 14 Nucleic Acids Research. Increased levels of the protein stop developing brain cells from growing and may cause the cells to commit suicide. A drug that inactivates p53 stopped brain cells from dying, Zhang said. Such p53 inhibitors could help protect developing brains in babies infected with Zika. But researchers would need to be careful giving such drugs because too little p53 can lead to cancer.
Zika also makes small RNA molecules that interfere with production of proteins needed for DNA replication, cell growth and brain development, Zhang said. In particular, a small viral RNA called vsRNA-21 reduced the amount of microcephalin 1 protein made in human brain cells in lab dishes. The researchers confirmed the results in mouse experiments. That protein is needed for brain growth; not enough leads to the small heads seen in babies with microcephaly. Inhibitors of the viral RNAs might also be used in therapies, Zhang suggested.
