BALTIMORE — When it comes to swimming sperm, it’s not every man for himself. Instead, sperm form groups that swim together, a bit like schools of fish or flocks of birds, physicists have observed.
Understanding the physics underlying such behavior in animals is difficult because their actions arise in part from cognitive processes — birds, for instance, can see what their neighbors are doing and adjust their flight path accordingly. But with sperm, group swimming emerges from the physics of the medium in which they swim, Chih-Kuan Tung of North Carolina A&T State University in Greensboro said in a news conference March 16 at a meeting of the American Physical Society. That makes sperm a simpler system for studying the physics behind a form of coordinated biological action. “They don’t think,” Tung said. “So whatever interaction is happening, we can quantitatively describe it.”
Sperm don’t form groups in ordinary water, Tung said, but they do in viscoelastic fluids such as the mucus of mammalian reproductive tracts. A viscoelastic fluid combines resistance to flow with the ability to restore its previous state when disturbed. Tung and colleagues created such elasticity by adding a polymer to the fluid used for testing the swimming ability of bulls’ sperm. Those experiments showed that it’s the elasticity, not the viscosity, that encourages collective swimming.
Further work will be needed, Tung said, to determine whether such group swimming confers an advantage to sperm seeking an egg. In any event, the new understanding of sperm dynamics could lead to improved methods for in vitro fertilization procedures, he said.
Sometimes science does not move fast enough, despite much hard work and effort. That’s true in the case of the Zika virus outbreak currently marching through the Americas. As we report in a collection of stories, much remains unclear, including the relationship between Zika infection and microcephaly and how best to combat the mosquitoes that spread the disease. So far, however, evidence does suggest that this little-known (and previously largely ignored) virus may indeed target the nervous system, probably triggering Guillain-Barré syndrome in a small percentage of patients. The virus could even pose as-yet undiscovered health risks that may take years to untangle. While scientists will no doubt eventually be able to answer many of the public’s pressing questions, it may be too late for many. It’s not a global emergency, but the public is also apparently impatient with science’s progress on providing practical advice about the human microbiome — the collection of bacteria and other microorganisms that live in and on us. This issue features two articles about new results from this hot field. Laura Sanders details surprising ways that gut microbes can meddle with the brain, hinting that certain microbial mixes may influence depression and other mental disorders. And Meghan Rosen describes the microbiome’s role in malnutrition, suggesting that resetting children’s microbes may be a useful treatment. It’s hard not to conclude that manipulating the bacteria in your body could offer a path to better health and happiness. Judging from the shelves at Whole Foods, that is what many makers of probiotic supplements would like you to believe. And it may well turn out to be true — studies have linked the microbiome to metabolic and digestive issues such as obesity, irritable bowel syndrome and inflammatory bowel disease. But science hasn’t yet come up with broad recommendations for the best ways to tend your personal microfloral garden. And since the Food and Drug Administration regulates supplements as foods, not as medicines, probiotic pills may vary in quality and even in actual ingredients; makers don’t have to prove that probiotics are safe or effective.
Notably, none of the researchers that Sanders asked while reporting “Microbes and the mind” said that they regularly take probiotic supplements. They also said that any effects on the brain, while fascinating, are probably subtle for most people — otherwise you’d notice a mood change every time you took antibiotics. In Rosen’s story about malnutrition, researcher François Leulier says: “We can envision some therapy solutions, but we’re still at the basic research level.” It’s just too early to start megadosing, he says, even for very sick kids.
To fill in the gap, people look to anecdote. Or, sometimes knowingly, they engage in uncontrolled self-experiments with an N of 1, fueled by the Internet (see the website Quantified Self) and DIY culture. The data gleaned from these personal trials may help individuals, but they can’t answer big questions.
An eager public — and intriguing science — is propelling microbiome research along. Zika research is sprinting after an elusive and mysterious foe, trying to stop the damage from the virus and learn from a vast natural experiment. In both cases, science must move more swiftly if it is to catch up.
Northern Oklahoma is just as susceptible to a damaging earthquake within the next year as the most quake-prone areas of California. That’s because earthquakes are no longer just a natural hazard, the U.S. Geological Survey says. In its new quake hazards forecast released March 28, the agency for the first time has included artificially triggered seismicity.
An increased risk in the central United States largely stems from sites where fluids, such as wastewater from fracking, are injected underground (SN: 8/9/14, p. 13). Rising fluid pressure underground can unclamp faults and unleash earthquakes (SN: 7/11/15, p. 10). From 1973 to 2008, an average of 24 potentially damaging quakes rattled the central United States each year. From 2009 to 2015, an uptick in fracking activity helped skyrocket that number to 318 annual quakes on average, with a record-setting 1,010 tremors in 2015 alone. Around 7 million people currently live and work in central and eastern U.S. areas vulnerable to shakes stemming from earthquakes roughly above magnitude 2.7, USGS scientists estimate.
Human-caused quakes aren’t as powerful as their natural counterparts (the strongest induced quake in the United States clocked in at magnitude 5.6 in 2011 compared with the magnitude 7.8 San Francisco temblor in 1906, for instance). But the potential for more powerful shakes exists, the scientists warn. The new hazard assessment should help regulators revise building codes to better prepare for the rising risk.
There’s still enough forest left — if protected wisely — to meet the goal of doubling the number of wild tigers (Panthera tigris) by 2022, says an international research team.
That ambitious target, set by a summit of 13 tiger-range nations in 2010, aims to reverse the species’ alarming plunge toward extinction. Forest loss, poaching and dwindling prey have driven tiger numbers below 3,500 individuals.
The existing forest habitat could sustain the doubling if, for instance, safe-travel corridors connect forest patches, according to researchers monitoring forest loss with free, anybody-can-use-’em Web tools. Previously, habitat monitoring was piecemeal, in part because satellite imagery could be expensive and required special expertise, says Anup Joshi of the University of Minnesota in St. Paul. But Google Earth Engine and Global Forest Watch provide faster, easier, more consistent ways to keep an eye out for habitat losses as small as 30 meters by 30 meters (the space revealed in a pixel). Looking at 14 years of data, 76 major tiger landscapes altogether have lost less than 8 percent of forest, the researchers say April 1 in Science Advances. Finding so little loss is “remarkable and unexpected,” they write. But 10 of those landscapes account for most of the losses — highlighting the challenges conservationists, and tigers, face.
Scientists may have found the cosmic birthplace of an ultra-high energy neutrino. They point the finger at a blazar — a brilliantly luminous galaxy that shoots a jet of radiation in the direction of Earth — 9 billion light years away.
If the link between the blazar and neutrino is real, scientists would be closer to long-sought answers about where such power-packing particles come from. Violent astronomical accelerators boost some neutrinos to high energies, but scientists have never been able to convincingly identify their sources. Neutrinos are aloof elementary particles that rarely interact with other matter — they can sail straight through the Earth, and trillions of them zip through your body every second without a trace. On December 4, 2012, the neutrino in question (which scientists have affectionately nicknamed Big Bird) slammed into the Antarctic ice with an energy of around 2 million billion electron volts. The neutrino observatory IceCube glimpsed the aftermath of the collision and measured its energy with sensitive detectors embedded deep in the ice (SN Online: 04/07/14), leaving scientists hustling to pinpoint its source.
The blazar flared up at just the right time and place to be a prime suspect, researchers report in a paper accepted for publication in a peer-reviewed journal. The result, now available online at arXiv.org, strengthens the case that blazars are the source of such high-energy neutrinos, but it is no smoking gun.
After the neutrino was detected, a team of astrophysicists scoured the heavens for energetic galaxies with TANAMI, short for Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry, a network of telescopes peering into space at a variety of wavelengths. That team reported one likely candidate blazar.
But the candidate is not a surefire match, says IceCube leader Francis Halzen of the University of Wisconsin–Madison, who was not involved with the analysis. IceCube could determine the neutrino’s direction within only about 15 degrees on the sky, and the blazar flare-up continued for several months. The probability of such a chance concurrence between an unrelated neutrino and blazar is about 5 percent, the researchers say — too big to rule out chance. “It’s a very intriguing result,” says Halzen “but it’s not a proof.”
The matchup between the blazar and neutrino is noteworthy, even though the researchers can’t fully rule out the possibility that the match is a fluke, says astrophysicist Xiang-Yu Wang of Nanjing University in China, who was not involved with the research. “Given that the two events are very unique … I think it’s convincing.” Wang and colleagues have expanded on the result: In a paper accepted for publication in Physical Review Letters, they use the difference in arrival time between the neutrino and light from the blazar’s outburst — assuming the two are related — to test Einstein’s special and general theories of relativity. Certain theories of quantum gravity predict a delay in the arrival of a neutrino. (Einstein came out unscathed.) The authors of the blazar study declined to comment on the result, citing the embargo policy of the journal where the paper will be published.
To convincingly identify a blazar as the source of a neutrino, Halzen says, scientists will need a better measurement of the neutrino’s direction, connected to a short-lived blazar outburst. In the future, Halzen says, IceCube will send out “astronomical telegrams” when it detects a neutrino, directing telescopes to take a look, perhaps catching a blazar in the act.
The U.S. Environmental Protection Agency has a methane problem — and that could misinform the country’s carbon-cutting plans. Recent studies suggest that the agency’s reports fail to capture the full scope of U.S. methane emissions, including “super emitters” that contribute a disproportionate share of methane release. Those EPA reports influence the country’s actions to combat climate change and the regulation of methane-producing industries such as agriculture and natural gas production.
With EPA’s next annual methane report due to be published by April 15, early signs suggest that the agency is taking steps to fix the methane mismatch. A preliminary draft of the report revises the agency’s methane calculations for 2013 — the most recent year reported — upward by about 27 percent for the natural gas and petroleum sectors, a difference of about 2 million metric tons. Yet it’s unclear how that and other revisions will factor into final methane emission totals in the upcoming report. The draft estimates that U.S. methane emissions from all sources in 2014 were about 28 million metric tons, up slightly from the revised estimate for 2013 and well above the original 2013 estimate of 25.453 million metric tons. But the totals in the draft don’t include updates to emission estimates from the oil and gas industry. “EPA is reviewing the substantial body of new studies that have become available in the past year on the natural gas and petroleum sector,” says EPA spokesperson Enesta Jones. The agency is also gathering feedback from scientists and industry experts to further improve their reporting.
Methane, which makes up the bulk of natural gas, originates from natural sources, such as wetlands, as well as from human activities such as landfills, cattle ranches (SN: 11/28/15, p. 22) and the oil and gas industry. Globally, human activities release about 60 percent of the 600 million metric tons of methane emitted into the atmosphere each year. Once in the air, methane prevents some of Earth’s heat from escaping into space, causing a warming effect. Methane emissions currently account for about a quarter of human-caused global warming.
The EPA’s underestimation of U.S. methane emissions comes down to accounting. EPA samples emissions from known methane sources, such as cows or natural gas pipelines, and works out an average. That average is then multiplied by the nation’s number of cows, lengths of pipe and other methane sources. Results from this method disagree with satellite and land-based observations that measure changes in the total amount of methane in the air. A 2013 report in the Proceedings of the National Academy of Sciences found that U.S. methane emissions based on atmospheric measurements are about 50 percent larger than EPA estimates (SN Online: 11/25/13). EPA’s reports don’t just misjudge the scale of emissions, they also miss the long-term trend, recent work suggests. EPA reported that U.S. methane emissions remained largely unchanged from 2002 to 2014. But researchers report online March 2 in Geophysical Research Letters that emissions of the greenhouse gas rose more than 30 percent over that period. The United States could be responsible for as much as 30 to 60 percent of the global increase in methane emissions over the last decade, the study’s authors conclude. “We’re definitely not a small piece of that pie,” says Harvard University atmospheric scientist Alex Turner, who coauthored the study. Correctly tracking methane is important, Turner says, because over a 100-year period, the warming impact of methane is more than 25 times that of the same amount of CO2. Methane levels have also risen faster: Since the start of the industrial revolution, methane concentrations have more than doubled while CO2 has risen more than 40 percent.
While methane is more potent than CO2, there is about 200 times less methane in the atmosphere than CO2. Furthermore, methane stays in the atmosphere for only around 12 years before being absorbed by soil or breaking apart in chemical reactions. “If we reduce methane emissions, the climate responds very quickly and global warming would slow down almost immediately,” says Cornell University earth systems scientist Robert Howarth. “CO2, on the other hand, has an influence that will go hundreds to even thousands of years into the future.”
Turner and colleagues tracked methane across the continental United States using land stations that measure methane in the air and satellite observations that record dips in the infrared radiation frequencies absorbed and reemitted by methane. The researchers compared these methane measurements with those taken over Bermuda and the North Pacific Ocean — places upwind of the United States and far from major methane sources.
From 2002 through 2014, methane concentrations over the continental United States grew faster than those over the oceans, the researchers found. The difference was most pronounced over the central United States, where methane concentrations rose nearly twice as fast as in the rest of the country. Natural gas drilling and production boomed in in the central United States during the period studied, though the researchers could not precisely trace the source of the additional methane.
Turner and colleagues say they’re now working with EPA to reconcile the methane estimates. EPA will provide small-scale estimates of methane emissions down to a 10-kilometer-wide grid. By combining that grid with space and land observations, scientists should be able to isolate where methane mismatches are the most pronounced.
While Turner’s research can’t pinpoint the exact origins of the additional methane, other studies point to the oil and gas industry. The numbers that the EPA uses to tabulate methane emissions assume that equipment is functioning as intended, says Stanford University sustainability engineer Adam Brandt. Malfunctioning equipment can spew huge amounts of methane. That became abundantly – and visibly – clear last October when the largest U.S. methane leak in history began in an underground storage facility near Los Angeles. The leak released 97,100 metric tons of methane, equivalent to the annual greenhouse gas emissions of 572,000 cars, before being permanently sealed in February, researchers estimated in the March 18 Science.
Super methane emitters are a big problem elsewhere, too, albeit typically much smaller than the California leak, researchers report in the June 2016 Environmental Pollution. Surveying emissions from 100 natural gas leaks around Boston, the researchers found that 7 percent of leaks contributed half of the total methane released. In 2014, a different research team reported in Environmental Science & Technology that 19 percent of pneumatic controllers used at natural gas production sites accounted for 95 percent of all controller emissions.
Monitoring and quick repairs can stamp out rogue methane sources quickly, Brandt says. “This is a problem that’s easier to fix than it is to understand,” he says.
Neither a giant asteroid nor a gradual die out can take full blame for dinosaurs’ demise.
Rather, the culprit may be both, two new studies suggest.
Tens of millions of years before the asteroid delivered its killer blow some 66 million years ago, the number of dinosaur species had already begun to drop, researchers report online April 18 in the Proceedings of the National Academy of Sciences. But not all dino groups were in decline, including some maniraptoran dinosaurs, a different group of researchers suggests online April 21 in Current Biology. At first glance, the two studies seem to conflict, but “they can coexist,” says paleontologist Michael Benton, who coauthored the PNAS paper. Both studies add to what has become an increasingly intricate picture of dinosaurs’ final days.
“Things are a wee bit more complicated than we used to think,” says Benton, of the University of Bristol in England.
In the 1960s and ‘70s, scientists generally believed that dinosaurs petered out after a long, gradual decline. That view took a U-turn in 1980, when researchers proposed that, instead, an asteroid impact might have suddenly triggered the extinction. “The flip-flop was quite extreme,” Benton says of the changed thinking. “Dinosaurs went from long-term decline to instant death.”
What actually happened, he says, is probably more nuanced. Benton and colleagues analyzed the number of dinosaur species emerging and going extinct over a huge timescale: roughly 175 million years. Around 40 million to 50 million years before the mass extinction, dinosaurs started losing species faster than they were gaining new ones, the researchers found. This loss in diversity could have made it harder for dinosaurs to bounce back from the asteroid’s catastrophic impact.
“This doesn’t in any way attack the importance of the impact,” Benton says. But across the board, he says, dinosaur species numbers were dwindling. At least two groups, however, seemed to buck the trend. Hadrosaurs (duck-billed dinosaurs) and ceratopsids (the group that includes Triceratops) were booming up until the end, the team found. According to the Current Biology analysis, toothed maniraptorans (small birdlike relatives of velociraptors) were thriving, too. A detailed examination of more than 3,000 of these dinosaurs’ teeth suggests that these dinos’ ecosystem was pretty stable millions of years before the extinction, says study coauthor Derek Larson, a paleontologist at the Philip J. Currie Dinosaur Museum in Alberta and the University of Toronto.
Larson and colleagues looked for variations in the teeth’s dimensions, and the size of tooth serrations. Then they determined how much that variation changed over time. Big changes could be a hint that these dinos were on the decline, Larson says. But instead, “things basically stayed the same through the last 18 million years of the Cretaceous,” he says.
Toothed maniraptorans “seemed to be doing just fine right up until the extinction,” says University of Oxford paleobiologist Roger Benson, who was not involved in either study.
Larson’s team wondered why the toothed, meat-eating maniraptorans went extinct after the impact while their relatives — the beaked ancestors of modern birds — didn’t. The answer could be dietary, the researchers propose. They analyzed the diets of modern birds to try and figure out what an ancestral bird might have eaten. It probably relied on seeds, Larson says, a hardy food source that could have lasted for decades.
Seeds might have sustained ancient birds through a “nuclear winter,” the debris-darkened skies that could have blotted out the sun following an asteroid impact. When hoards of plants and animal species died out, and dinosaurs ran out of food, he says, “the only resource that would have been reliable and available would have been seeds.”
Herbivores beware: Take a bite out of bittersweet nightshade (Solanum dulcamara), and you might have an ant problem on your hands. The plants produce a sugary goo that serves as an indirect defense, attracting ants that eat herbivores, Tobias Lortzing of Berlin’s Free University and colleagues write April 25 in Nature Plants.
Observations of wild nightshade plants in Germany suggest that plants that ooze goo attract more ants (mostly European fire ants, or Myrmica rubra) than undamaged plants. In greenhouse experiments, those ants fed on both the goo and roving slugs and flea beetle larvae, substantially reducing leaf damage. Leaf-munching adult flea beetles and, to a lesser degree, slugs prompted the goo production. The ants didn’t attack the beetles but did protect the plant from slugs and beetle larvae.
Plenty of other plants produce defensive nectars via organs called nectaries, and nightshades’ bleeding may be a unique, primitive version of that protective strategy, the scientists report.
Labrador retrievers tend to be more overweight and keen to scarf down their kibble than other dog breeds. Eleanor Raffan of the University of Cambridge and her colleagues chalk this trend up — least in part — to a suspect gene.
The team found that, among a small group of assistance dogs, a form of a gene called POMC that was missing a chunk of DNA was more common in obese Labs than in lean ones. This held true on a larger scale, too: Out of 411 Labs in the United Kingdom and United States, 22 percent carried the deletion mutation. Looking across other breeds, only Labradors and flat coat retrievers, a close relative, carried the gene variant, which also correlated with greater weight and food begging tendencies, the team reports May 3 in Cell Metabolism.
POMC plays a role in a metabolism pathway, and the deletion may inhibit the production of proteins that regulate hunger, the researchers suspect. (That might explain why the variant turned up in about 75 percent of assistance dogs, which are trained using food motivation.)
Not all cosmic mysteries lie light-years away. Some secrets are being unearthed on our nearest neighbor, about a quarter of a million miles from home.
For almost seven years, NASA’s Lunar Reconnaissance Orbiter has been keeping a close eye on the moon. During its tenure, the spacecraft has cataloged craters, pinpointed subsurface deposits of water ice and found evidence of recent volcanic activity. It has even witnessed crashes by three other spacecraft. (One, LCROSS, launched a plume of ejecta from the south pole that scientists searched for water vapor.) “No other mission has orbited the moon for as long as LRO has,” says Noah Petro, a geologist at NASA’s Goddard Space Flight Center in Greenbelt, Md. Constant lunar vigilance has “really pushed our understanding of how the moon changes today, over the last billion years and what happened early on.” A July 15 special issue of Icarus celebrates the mission’s many discoveries, which fill out not only the moon’s story, but also reveal how Earth and other rocky planets have been pummeled by space debris over the last 4 billion or so years.
When LRO launched on June 18, 2009, its goals were more modest. The spacecraft was sent to scout landing sites for future astronaut expeditions, hunt for resources such as water and better understand the radiation hazards that human crews would face. Since completing its original one-year assignment, the mission has been extended several times. LRO plans to stay busy through September, and the team has asked NASA for two more years. Water ice turned up in some unexpected places. Other spacecraft had previously seen hints of water, but none could map precisely where it was. Researchers suspected that water lay within permanently shadowed craters at the poles, and LRO did find evidence of ice there. But LRO also found that not all shady spots harbor water, and not all water is found in the shadows — some appears to hide under soil that sits in direct sunlight.
“That was bit of a surprise,” says LRO project scientist John Keller, also at Goddard. Looking at temperature alone, it seems, isn’t enough for understanding the history of water on the moon. In the polar shadows, where temperatures hover around –250° Celsius, water ice can endure for billions of years. But elsewhere, water may have been trapped more recently and protected by the terrain. “There’s an interplay with time, temperature and topography underlying this water story,” says Keller. How the various water deposits are implanted and shuffled about is one enduring puzzle. How small subterraneous pockets stayed warm for so long after the moon formed is another. Lava oozed on the surface in the last 100 million years, judging by smooth, dark terrains that are sparsely cratered. “This flies in the face with what was known about the moon,” Petro says. “We thought lunar volcanism ended about a billion years ago.” Some changes are much more recent. In 2013, Earth-based telescopes detected a flash of light from the moon. LRO checked it out and found a new crater 18 meters across. “What was surprising was how far the ejecta went,” Keller says. Debris had been tossed 35 kilometers — much farther than expected from a space rock estimated to be only about a meter wide.
Understanding what’s currently hitting the moon and the traces those objects leave is crucial to interpreting the history of impacts plastered across the lunar surface; similar impacts also affected Earth but most have been erased by weather and geologic forces. “The moon is our way of studying the history of the Earth since the creation of the Earth-moon system,” Petro says.
One of the seven instruments that LRO carries is a laser altimeter, a beam of light that scans and maps the surface in exquisite detail. “That’s been a game changer,” says Simone Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colo. “We can use the topography data to find old degraded craters that otherwise would not be easily detected in imagery.”
Detailed maps reveal craters on top of other craters, laying out a rough sequence of when things hit the moon. And astronauts have brought back samples from some of these terrains, allowing researchers to use radiogenic dating to figure out when craters formed. That in turn supplies a record of what was smacking into other planets and asteroids. “We have a deep understanding of collisions going back to the beginning of the solar system,” says Marchi. “That can only be done with the moon.”
