A half-century after scientists first introduced a vaccine to combat measles, the disease has been eliminated from a swath of the globe stretching from Canada to Chile — and all the countries in between.
The region is the first in the world to have eliminated the viral disease, the Pan American Health Organization and World Health Organization announced September 27. That’s different from eradication, which means an infectious disease has been scrubbed out permanently, worldwide. So far, only smallpox has been eradicated.
Though measles outbreaks still crop up occasionally in the Americas (this year 54 people have contracted the disease in the United States), they stem from travelers bringing the virus in from other parts of the world. A home-grown outbreak in the Americas hasn’t occurred since a 2002 outbreak in Venezuela.
Because measles still circulates widely elsewhere, vaccination remains crucial, PAHO Director Carissa Etienne noted in a press statement. “Our work on this front is not yet done,” she said. “We cannot become complacent with this achievement but must rather protect it carefully.”
Screens are everywhere. They adorn walls, perch on the backs of car seats and warm our hands. No one knows yet whether all of these screens, and their alluring displays and connections to the world, have any long-term effects on us. There is one group of people, though, for whom these ever-present screens may be particularly worrisome — kids.
Earlier recommendations on children’s screen time from the American Academy of Pediatrics were cut and dry. For kids under 2, screens were best avoided. Older kids got no more than two hours a day.
On October 21, scientists announced more nuanced guidelines in an attempt to guide parents on how screens of all sorts — TVs, tablets, phones and electronic readers — ought to fit into children’s lives. By moving away from the finger-wagging and diving deep into the shades of gray, the recommendations put more onus onto parents to decide what’s best for their families. These new suggestions are “a vast improvement over what we — pediatricians — have done in the past,” says pediatrician Michael Rich of Harvard Medical School.
For young children, the new guidelines offer concrete time limits. For children 5 and older, the recommendations are essentially aimed at having parents understand the value of media, how that changes with age, and perhaps most importantly, the importance of media-free time.
“We want them to focus on getting enough sleep, play, family routines, conversation, social time and exercise,” says pediatrician Jenny Radesky of the University of Michigan in Ann Arbor, who coauthored one of the new policy statements. “And we recommend [parents] try to do this by creating unplugged times of day and zones of the home, prioritizing family time and play, and having rules like device curfews.”
As a way to move closer to those media-free zones, researchers offer some recommendations for young children based on the latest scientific literature:
Avoid digital media use for children younger than 18 months to 24 months old (with the exception of video chatting). If you want to introduce media to 18- to 24-month-olds, look for high-quality programs and watch the programs together. For kids 2 to 5 years old, limit screen use to an hour a day of high-quality programming, and watch the programs together so you can help them understand what they see and relate it to the world. Keep bedtimes, meals and play time media-free. That means parents, too, who have been known to become engrossed in their own screens and ignore their company. Screens should be off an hour before bed, and they shouldn’t be in bedrooms. Other recommendations include keeping a close eye on kids’ media content, turning off TVs or other screens when you’re not using them and avoiding screens as a way to regularly calm your child.
For children 5 and up, the guidelines no longer have a strict time limit. Instead, it puts the onus on parents to figure out their family’s plan. Losing the previous policy’s time limit may be a mistake, says pediatrician Victor Strasburger of the University of New Mexico School of Medicine, who helped write those earlier recommendations. “I was sorry they took out the two-hour recommendation. … I think the academy got a little gun-shy,” he says, afraid of offending parents whose children get way more than two hours of media a day.
The lack of clear limits for older children might be frustrating for parents who want simple rules. Rich sees these frustrations up close as the “Mediatrician,” an advice columnist who answers parents’ questions about digital health. “By being so respectful, [the new policy] runs the risk of not sending its message,” Rich says. But that flexibility may be helpful, because no two families are alike. “The best judge of this is ultimately the parent,” he says.
The question of how to fit media into children’s lives is really difficult. “We are dealing with two moving targets,” Rich says: the developing child and the developing media landscape. That means that simple answers don’t exist. And after all, parenting is more of an art than a science.
Scientists are still struggling with the distinctions between the different types of media — whether a TV show has different effects than an interactive app, for instance. But so far, there’s no evidence that kids under 2 can learn from apps, despite any “educational” marketing, Radesky says.
The guidelines address both media quality and quantity. High-quality programs “engage little minds on their learning edge, don’t use too many bells and whistles or fast editing to try to keep viewers’ attention, and craft their content for a dual audience,” Radesky says. These types of shows can be good sources of knowledge for preschoolers and their parents. Quantity matters too, especially as media becomes overused. Radesky has had parents tell her about putting their 2-year-old with a language delay in front of educational TV shows for five to six hours a day. “We really want to discourage parents from doing that,” she says.
For some families, the guidelines may be too lenient. For others, they may be too restrictive. And others may be overwhelmed at the prospect of investing the time and energy to really watch their children’s media use. But the principles behind these guidelines are solid. It’s definitely true that in addition to entertainment, media can offer rich learning experiences that would be otherwise unattainable. Even so, kids need to sleep, play, talk and explore their wondrous world — in real life.
Leprosy has been hiding out in red squirrels in Great Britain and Ireland, though the painful and disfiguring disease has rarely been transmitted between humans there since the Middle Ages.
The endangered bushy-tailed rodents (Sciurus vulgaris) have tested positive for leprosy-causing bacteria in several locations around the British Isles, researchers report November 11 in Science.
“It goes to show that once a disease has become extinct in humans, it could still exist in the environment if there was a suitable reservoir,” says study coauthor Stewart Cole, director of the Global Health Institute at the Swiss Federal Institute of Technology in Lausanne. In this case, squirrels seem to be ideal incubators for leprosy bacteria. Until recently, leprosy, clinically known as Hansen’s disease, was thought to be transmitted only between humans. But in 2011, a team of scientists that included Cole found the disease in nine-banded armadillos in the southern United States (SN: 5/21/11, p. 9).
“One of the things we’ve never really understood about leprosy is how it can persist in populations at such low prevalence for such long periods of time,” says Richard Truman, a microbiologist at the National Hansen’s Disease Program in Baton Rouge, La., who wasn’t part of the study. The discovery that leprosy bacteria linger in various animal populations might help explain the disease’s sticking power in humans.
The relatively high prevalence of leprosy bacteria found in British red squirrel populations is also surprising, Truman says. Cole and his collaborators analyzed 110 red squirrel carcasses from Scotland, Ireland and two islands off the coast of England. All 13 of the visibly sick squirrels and 21 out of 97 seemingly healthy squirrels tested positive for the bacteria. Sick squirrels had skin lesions, patchy fur and nerve problems, similar to the symptoms seen in humans. The team found leprosy bacterium species Mycobacterium lepromatosis in squirrels from Scotland, Ireland, and the Isle of Wight, and Mycobacterium leprae in squirrels from remote Brownsea Island.
The strain found in the Brownsea Island squirrels is similar to the strain that made the rounds in medieval England, Cole says. That suggests the bacteria could have circulated in red squirrels for hundreds of years without changing very much (SN: 7/13/13, p. 18).
Today, more than 200,000 people are newly diagnosed with leprosy each year, mostly in Africa and Southeast Asia. But antibiotics, where available, easily clear up the infection. And up to 95 percent of people have some natural immunity to the disease, Truman says, so it’s not nearly as contagious as previously believed. So the odds of catching leprosy from a squirrel, an armadillo or another human are extremely slim. But since squirrels can carry other diseases too — such as rabies — it still might be best to observe the furry woodland creatures from a safe distance.
The moon is one tough satellite. With no atmosphere, it endures a barrage of incoming asteroids and comets that pit its surface with a constellation of craters. A new map (above) reveals 222 recent impact craters (in yellow), 33 percent more than simulations predicted. Scientists spotted the features by analyzing about 14,000 pairs of before-and-after images captured by the Lunar Reconnaissance Orbiter from 2009 to 2015. (Red dots note new craters whose impacts were observed from Earth.)
The craters — up to 43 meters in diameter — were probably formed by small meteoroids crashing into the crust. Using the image pairs, the researchers created ratio images, which highlight how the impacts alter the reflectance of the moon’s surface. That perspective illuminated the starburst debris patterns around the craters (below, left). The scientists also found about 47,000 “splotches,” faint marks several to tens of meters across (below right, before and after shown). Most result from secondary debris being jettisoned by impacts and spattering the surface, the researchers propose in the Oct. 13 Nature. Those splotches would “churn” the upper two centimeters of lunar soil in about 81,000 years, more than 100 times faster than previous predictions that didn’t include the smudges, researchers say. That revelation could improve interpretations of remote-sensing data and help engineers design equipment to better withstand the occasional speckling of soil, says study coauthor Mark Robinson, a planetary geologist at Arizona State University in Tempe. “All of the images we’re taking … and the discoveries we’re making are feeding forward into future human exploration of the moon,” he says.
Microcins MĪ-kro-sins n. Bacterial proteins that kill rival bacteria
Competition is cutthroat in the crowded world of the intestines, so bacteria have evolved ways to kill rivals for a survival advantage. One strain of bacteria, called Escherichia coli Nissle 1917, has tiny proteins called microcins that may help E. coli’s host fight pathogens that cause gut inflammation, researchers at the University of California, Irvine report online October 31 in Nature.
Microcins take action only when bacteria are starved for iron, which happens in an inflamed gut. The proteins go after bacteria, many of them pathogens, that make iron-scavenging proteins, the researchers found. E. coli Nissle’s microcins killed diarrhea-inducing bacteria called Salmonella enterica in the guts of infected mice. Microcins also helped Nissle outcompete a different, nasty strain of E. coli.
One of biology’s biggest achievements of 2016 was intentionally as small as possible: building a bacterium with only 473 genes. That pint-size genetic blueprint, the smallest for any known free-living cell, is a milestone in a decades-long effort to create an organism containing just the bare essentials necessary to exist and reproduce. Such “minimal genome” cells might eventually serve as templates for lab-made organisms that pump out medicines, make innovative chemicals for industry and agriculture, or churn out other molecules not yet imagined. The project also identified genes crucial for the microbe’s survival yet largely unfamiliar to science, highlighting major gaps in researchers’ grasp of life’s playbook.
The newly engineered bacterium was praised as a technical triumph. In 2010, researchers at the J. Craig Venter Institute in La Jolla, Calif., had stitched together a copy of the entire genome of the bacterium Mycoplasma mycoides and popped it into the cell of another bacterium whose genome had been removed. But that “synthetic cell,” dubbed JCVI-syn1.0, contained a full copy of an existing genome. With more than 1 million chemical building blocks of DNA, including 901 genes, it was far from minimal. The latest version, JCVI-syn3.0, reported in March in Science (SN: 4/16/16, p. 6), has roughly half that much DNA. It’s also the first cell built using human design principles: One segment of the genome has genes for various processes, such as DNA repair, grouped together rather than scattered willy-nilly. Abandoning the untidiness of evolution for a logic-driven blueprint enables a “plug and play” approach, says Daniel Gibson, a member of the JCVI team. To tinker with a metabolic process such as glycolysis, for example, “Rather than changing one gene, then another, then another, you could pop out a whole module and then pop in a new one.”
Making such fundamental changes to the genome while still getting a functioning cell is noteworthy, says genome scientist George Church of Harvard University. “They could have found that, no matter what they did putting it together, it broke,” Church says.
The potential of synthetic cells is enormous, says Claudia Vickers, a biotechnologist at the Australian Institute for Bioengineering and Nanotechnology in Brisbane. Scientists have succeeded in engineering existing organisms such as yeast to help make, for example, malaria drugs. Now little cellular factories designed to be highly efficient and tailored to specific tasks are within sight, Vickers says. The techniques used to build JCVI-syn3.0, especially when considered alongside other engineering tools such as the recently developed CRISPR/Cas9 system (SN: 9/3/16, p. 22), are a meaningful step toward the once-distant goal of self-replicating minimachines. “It’s important for the future it allows us to imagine,” Vickers says.
Since announcing JCVI-syn3.0, the team has used the same engineering techniques to turn the fast-growing bacterium Vibrio natriegens into a laboratory workhorse. The engineered Vibrio — dubbed Vmax — cuts the time it takes to do particular lab experiments in half compared with the original, Gibson says.
The minimal genome effort also aims at a larger philosophical question: What is life? In a lecture in 1984, origin-of-life expert Harold Morowitz discussed how studying the small and simple Mycoplasma genome might invigorate basic biology in much the way that studying the hydrogen atom sharpened questions for physics and chemistry. (Morowitz died in March, two days before the JCVI-syn3.0 work was published online.)
Many scientists, for example, were stunned to learn that JCVI-syn3.0 had 65 genes with no known function that were nevertheless required for survival. “This is one of our best studied organisms, and we haven’t the foggiest idea what those genes are doing,” says evolutionary genomics expert Laurence Hurst of the University of Bath in England. “It’s a brilliant result.”
As science journalists look back on the top stories of the year, scientists push on, asking the next questions and chasing fresh data. What big discoveries might they deliver in 2017? Science News writers reveal what they are watching for — and hoping for — in the year ahead. Bruce Bower Behavioral Sciences “I look forward to seeing where the reproducibility debate goes,” says Bruce Bower, referring to recent reports that many findings in psychology (and other sciences) don’t hold up in repeat experiments (SN: 4/2/16, p. 8). Some psychology journals now publish multilab replication efforts that often challenge influential findings, such as the claim that willpower decreases the more you use it. Bower wonders whether the current hubbub over failed replications will prompt psychologists, as well as researchers in other disciplines, to experiment with new ways of doing science. “I would be lying if I said I was optimistic, but I’m ready to be proven wrong,” says Bower. He believes social and cognitive psychology rely far too heavily on significance testing and too many researchers don’t generate and test alternative explanations for statistically significant results. “It’s a general problem of not developing and integrating theories.” As for the types of stories he looks for, Bower says he chases anything that sheds light on what makes us human — what distinguishes us from other species and what unites us, both biologically and culturally.
Emily Conover Physics Emily Conover isn’t yet over the discovery of gravitational waves, which is “still the darling of the physics world,” she says. But in 2017 she’ll be focused on experiments seeking “weird stuff in physics.” Neutrino experiments will be searching for differences between matter and antimatter — “a big deal for how everything in the universe came to be,” she says. Researchers with the dark matter experiment ADMX plan to unveil results in their latest search for the light, electrically neutral and still hypothetical axions. “People are focusing on axions because WIMPs aren’t showing up.” And Fermilab’s Muon g-2 experiment will measure the magnetic properties of the muon, a particle like an electron but much more massive. “We could get something new anytime,” Conover says. While particle physicists wait for a big find to shake up the field, researchers studying quantum materials are making steady progress. In 2017, scientists will take that quantum prowess to space. When it arrives at the International Space Station, the Cold Atom Laboratory will offer a stable and isolated environment to study quantum systems known as Bose-Einstein condensates at temperatures as low as a tenth of a billionth of a degree above absolute zero.
Christopher Crockett Astronomy Space missions across our solar system will fill the news in 2017, says Christopher Crockett, with NASA’s Juno probe building a 3-D picture of the inside of Jupiter (SN: 6/26/16, p. 16) and the European Space Agency’s ExoMars orbiter looking for trace gases in the Red Planet’s atmosphere. Cassini’s mission at Saturn will be “the most fun,” says Crockett. “It is the end of the mission, so the engineers are getting braver with the spacecraft.” Planetary scientist Glen Stewart of the University of Colorado Boulder calls it “kamikaze” stuff. “They are taking the spacecraft to places it was never designed to go,” Crockett says. “They are going to start flying close to the rings. And early in 2017, they are going to use the gravity of Titan to slip between the rings and Saturn, and will eventually dive toward the planet.” The findings could fill in details of how the solar system formed and evolved.
August’s solar eclipse (SN: 8/20/16, p. 14) will be big news, Crockett says, and the Event Horizon Telescope (SN: 5/31/14, p. 16) could make headlines, too. The project has linked together telescopes around the world to build a virtual radio dish as wide as Earth that could take a picture of the supermassive black hole at the center of the galaxy. “What they are trying to do is phenomenally difficult,” Crockett says. “We’ll see if that actually works.”
Tina Hesman Saey Molecular Biology “Everybody is CRISPRing everything,” says Tina Hesman Saey, referring to the breakout gene editor that made headlines in 2015. There are efforts to modify chickens to produce hypoallergenic eggs and to create mushrooms that don’t brown. Pigs are being developed to grow organs for transplant into people. Researchers are using CRISPR/Cas9 (SN: 9/3/16, p. 22) as a tool to investigate which genetic variants may cause heart disease and cancer and to learn more about how genes turn on and off.
Still more exciting developments are on the way. Clinical trials in people using CRISPR have begun and more will start in 2017 (SN Online: 11/16/16). “If researchers can actually make headway on curing sickle cell disease or muscular dystrophy, which has shown promise in animals, that would be amazing,” Saey says. She is also anxious to see progress in making functioning gene drives, engineered DNA designed to propel itself through generations of organisms (SN: 12/12/15, p. 16). “What form will it take and would we dare use it? So much of my beat seems to be, ‘We can do these things, but should we do them?’ ”
Saey also believes that there will continue to be more avian flu outbreaks and other emerging diseases. “Bats will get blamed for a lot, even though it is probably not their fault,” she says.
Susan Milius Life Sciences After an exciting year in mosquito science, Susan Milius says she is “suffering through the reruns until we get to Season 2 of great mosquito research.” The basic biology of these diverse insects received quite a bit of attention in 2016 because it mattered for predicting how Zika virus would spread. In particular, Milius wonders how the conflicting results will sort out between U.S. labs that report that a common Culex mosquito can’t transmit Zika and labs in China, Brazil and Canada (work still ongoing) that suggest the species can (SN: 10/29/16, p. 13). “Is it differences in the mosquitoes? In the viruses? What’s going on?” In 2017, a long-debated pest-control test in Florida could release the first genetically modified mosquitoes to fly free-range in the United States. “We are at an interesting time in the application of biology,” Milius says.
But the best stories in organismal biology are the ones you don’t predict: “Given several billion years, all that mindless happenstance evolution has veered way into the improbable.” She points to 2016’s finding that melatonin makes midshipman fish sing (SN: 10/29/16, p. 4). And what’s been supposedly known for years — that spiders can’t hear airborne sounds from across the room (SN: 11/12/16, p. 9) — “can turn out to be just wonderfully wrong.”
Meghan Rosen General Assignment “The world will be keeping a close eye on Puerto Rico,” says Meghan Rosen, where some 2,700 pregnant women have been infected with Zika. As those women give birth, researchers will learn even more about the virus and related birth defects. In the meantime, “there are a handful of vaccines beginning to be tested in humans,” Rosen says (SN: 9/3/16, p. 17). Results of safety testing on a DNA vaccine developed by the National Institutes of Health are expected in 2017. If those data are encouraging, the vaccine could move to Phase II clinical testing. A different vaccine, which uses a purified inactivated form of Zika, also began testing late in 2016. Even with success, Rosen notes, it’s unlikely a vaccine will be widely available before 2018 or 2019. “It sounds like forever,” she says, “but researchers are really hustling along.”
Zika is a topic “I’ll want to follow for years to come,” Rosen says. But she also expects to cover lighter material in 2017 — her typical territory includes dinosaurs and robots. The new journal Science Robotics has launched, and Rosen looks forward to developments in one area in particular: soft robots. “These squishy machines eschew the clunky mechanical bits of old-school robots, instead relying on soft materials such as silicone rubber,” she says. Such robots could offer one way to safely integrate machines into people’s live.
Laura Sanders Neuroscience “Our ability to figure out what the brain is doing, and to really influence it, is going to be a promising area in the coming year,” says Laura Sanders. The Brain Initiative, which launched to both skepticism and excitement in 2013 (SN: 2/22/14, p. 16), “is rolling on and picking up steam.”
Sanders will be tracking developments in new technologies, including neural dust, those miniature ultrasonic devices that recently demonstrated their ability to detect nerve activity in rats (SN: 9/3/16, p. 10). She’s also interested in ultrasound’s potential to influence neural activity, along with other approaches that work from outside the skull and so don’t require brain surgery. In a dramatic example, researchers reported in 2016 that they had helped a patient recover from a minimally conscious state through low-intensity ultrasound stimulation of the thalamus. “It’ll be interesting to see where that goes,” Sanders says. Still, there’s a long way to go between basic brain science and treatments.
Sanders — who was born in the analog age but has children who will be digital natives — is curious to find out how iPads and other digital devices are affecting kids’ brains. “Deep down I’m worried about it because I think there are so many valuable aspects of face-to-face communication,” she says. “The art of conversation is so different from texting.”
Thomas Sumner Earth Sciences “In climate news,” says Thomas Sumner, “2017 is almost certainly going to be cooler than 2016.” El Niño boosted global temperatures, but it has now ended — making it unlikely that 2017 will be another record breaker (SN Online: 6/9/16). “The last time we had a big dropdown, people started saying ‘Global warming doesn’t exist anymore.’ ” Sumner wants to be clear about the science up front: “There is natural variability. We will continue seeing temperature increases in the long run.”
In a special issue in Science News planned for early 2017, Sumner will take readers on a geologic journey back to the dinosaurs’ last days. A recent drilling expedition into the Chicxulub crater (SN Online: 11/17/16) is taking a shot at the long-standing, sometimes heated debate over what killed the vast majority of plant and animal species on the planet 66 million years ago. Did massive volcanic eruptions bring down the dinosaurs? Or did their end come from the fallout of an asteroid that struck Earth’s surface near the Yucatán Peninsula, leaving a crater as wide as New Jersey is long. “It’s a dino mass-murder whodunit,” Sumner says. The drilling team will probably pin down the energy released by the collision and will study the resulting environmental consequences. New clues may offer an answer or spark a whole new round of questions.
It’s kind of daring to write a science book about something that — you must remind your readers — doesn’t exist. That’s James Gleick’s task in Time Travel, an engaging and entertaining look at science that will always remain fiction.
It’s lucidly written, a breeze to read and erudite in assessing a vast range of literary and popular media treatments of time travel as dream and desire. Gleick starts with, and often returns to, H.G. Wells’ The Time Machine, the book (and later films) that introduced the concept of time travel in its modern science fiction sense. Much of Gleick’s account focuses more on time than travel, though — examining the mystery of time’s direction (SN: 7/10/15, p. 15) and the philosophy of time (as in, what is it?). One whole chapter discusses time capsules, which are not exactly as exciting as a TARDIS. But Gleick always turns back to time travel, if only to remind that it is fiction, not physics: “Time travel is a fantasy of the modern era.”
Before the 19th century, “time travel” rarely occurred to anybody, because time didn’t change things much. Activities in ancient and medieval times differed little from life in the 1700s. But then new technologies — steam engines, electricity, telephones among them — infused 19th century thinkers with visions of even more technological progress, and a future worth traveling to. Mark Twain’s A Connecticut Yankee in King Arthur’s Court was all about “the contrast of modern technology with the agrarian life that came before,” Gleick writes.
His tour of the time travel fictional corpus includes mentions of Looney Tunes and Elmer Fudd, Mr. Peabody’s WABAC machine and Arnold Schwarzenegger’s Terminator. In addition to thorough analysis of Wells’ Time Traveller, there are extended discussions of Robert Heinlein’s “By His Bootstraps,” Isaac Asimov’s The End of Eternity, and “Blink,” one of the most famous 21st century episodes of Doctor Who. At times, tidbits injected from films, novels and poetry seem too much, almost like a dictionary of famous time travel quotations, many quite lengthy. Sometimes you’d like to hear more from Gleick and less from everyone else.
It’s also a bit disappointing that Gleick only briefly discusses actual science. There is a vast scientific literature on time travel, including many proposals for how to do it, that Gleick mostly ignores. He does cite a well-known paper by physicist Kip Thorne and colleagues and offers a brief account of logician Kurt Gödel’s earlier work on time loops (possibly permitted by Einstein’s general relativity). And Gleick discusses Stephen Hawking’s “chronology protection conjecture” to emphasize once again that time travel really can’t happen.
Those who remember the rich depth of Gleick’s groundbreaking book Chaos and his insightful biography of Richard Feynman will find much less science here. But there is plenty of science fiction. And as Gleick points out, “the rules of time travel have been written not by scientists but by storytellers.”
Ecologists still don’t believe in fairies. But it may take magic to resolve a long-running debate over what causes the oddly regular spots of bare soil called fairy circles. A new approach now suggests combining the two main hypotheses.
Fairy circles, each among about six close neighbors, sprinkle arid grasslands in southern Africa and Australia “like a polka dot dress,” says ecologist Corina Tarnita of Princeton University. Two persistent ideas fuel debate over what’s making the arrays: stalemate warfare between underground termite colonies (SN Online: 3/28/13) or bigger plants monopolizing water (SN: 4/16/16, p. 8). “What if the reason that this debate is so long-lasting and it’s so hard to dismiss the other hypothesis is that both are right to a certain extent?” Tarnita asks. Termites, by themselves, can in theory cause the mysterious arrangements, Tarnita, Princeton ecologist Robert Pringle and colleagues conclude from a new mathematical model they developed. They then linked their insect model with one showing plant competition causing fairy circles. The combined approach unexpectedly predicted a previously undescribed regular “clumping” pattern among the plants between fairy circles, the team reports January 18 in Nature.
In aerial pictures of fairy circles, the plants look like an even sea of vegetation between bare spots. To see if the plant patterns were real, the researchers visited the Namib Desert in southern Africa. Local park personnel “were constantly confused,” Tarnita says, because visitors usually study the bare patches. The vegetation clumped as predicted, in roughly hexagonal arrays as the circles themselves do. That confirmation suggests the combined model was working, the researchers say.
Hexagonal arrangements show up repeatedly in nature as creatures crowd together — for instance, as bees arrange cells in honeycombs, Pringle says. In southern Africa, termite colonies might create circular bare spots when insect nibbling prevents plant growth above the nest. Colonies too evenly matched to destroy each other persist as neighboring disks of barren soil, eventually packing into roughly hexagonal arrays. But plants by themselves can make similar bare spots in harsh conditions, Tarnita explains. When a pioneer plant springs from dry, hot ground, for instance, opportunists follow, taking advantage of such benefits as the scrap of shade a pioneer casts. As these secondary plants grow bigger and suck up more of the limited water, they can create dead zones where nothing sprouts. Over time, these zones form hexagonal patterns, too. Termites plus plants are probably producing the effect in the Namib Desert, Tarnita says. But the results might not apply to other fairy circle hot spots, such as Australia, she cautions. The main message of the new paper is that “different processes can lead to the exact same pattern,” she says.
Two proponents of the long-standing theories aren’t convinced the termite and plant models should be combined. Termite advocate Norbert Jürgens of the University of Hamburg welcomes the part of the new model that social insects alone “clearly” can cause fairy circles. But he’s not sure the plant clumping between circles indicates anything important. “Yes, of course there are always small-scale patterns among neighboring plants that are caused by feedback mechanisms,” he says. “However, these do not cause fairy circles.”
Nor does the new paper convert an ecologist advocating plant competition as the driver of fairy circle formation. Just showing that termites by themselves could create arrays with six neighbors isn’t enough, says Stephan Getzin of the Helmholtz Centre for Environmental Research GmbH-UFZ in Leipzig, Germany. “The degree of ordering or regularity that is shown by their insect model is not as strong as the ordering of [real-world] fairy circles,” he objects.
What’s needed now to resolve the debate isn’t necessarily fairy dust. Tarnita says she’s hoping for outdoor experiments.
Salmonella bacteria don’t want your body to starve on their account. The microbes’ motives, though, are (probably) purely poop-related.
The body sometimes sacrifices appetite to fight off infection: Less energy for the host also means less energy for the pathogen. Understanding how bacteria cope with this tactic can inform treatments.
When it reaches the gut, Salmonella enterica bacteria can trigger this type of anorexic response in their host, making it a good model for how microbes deal with less food. Researchers at the Salk Institute in California investigated salmonella fallout in mice. In lab tests, they found that the bacteria aren’t as virulent when a mouse isn’t eating, and they use the vagus nerve, a superhighway connecting gut to brain, to encourage eating. The bacteria make a protein called SIrP that appears to block signals that dampen appetite.
Keeping a host well fed plays out in the pathogen’s favor, the researchers write January 26 in Cell. That food has to go somewhere, and excreted waste gives salmonella place to live and an opportunity to spread.
