In A.D. 185, Chinese records note the appearance of a “guest star” that then faded away over the span of several months. In 1572, astronomer Tycho Brahe and many others watched as a previously unknown star in the constellation Cassiopeia blasted out gobs of light and then eventually disappeared. And 30 years ago, the world witnessed a similar blaze of light from a small galaxy that orbits the Milky Way. In each case, humankind stood witness to a supernova — an exploding star — within or relatively close to our galaxy (representative border in gray, below).
Here’s a map of six supernovas directly seen by human eyes throughout history, and one nearby explosion that went unnoticed. Some were type 1a supernovas, the detonation of a stellar core left behind after a star releases its gas into space. Others were triggered when a star at least eight times as massive as the sun blows itself apart.
BOSTON — A fungus among us may tip the body toward developing asthma.
There’s mounting evidence that early exposure to microbes can protect against allergies and asthma (SN Online: 7/20/16). But “lo and behold, some fungi seem to put kids at risk for asthma,” microbiologist Brett Finlay said February 17 at a news conference during the annual meeting of the American Association for the Advancement of Science.
Infants whose guts harbored a particular kind of fungus — a yeast called Pichia — were more likely to develop asthma than babies whose guts didn’t have the fungus, Finlay reported. Studies in mice and people suggest that exposure to some fungi can both trigger and exacerbate asthma, but this is the first work linking asthma to a fungus in the gut microbiome of infants. Finlay, of the University of British Columbia in Vancouver, and his colleagues had recently identified four gut bacteria in Canadian infants that seem to provide asthma protection. To see if infants elsewhere were similarly protected by such gut microbes, he decided to look at another population of children with an asthma rate similar to Canada’s (about 10 percent). He and his colleagues sampled the gut microbes of 100 infants in rural Ecuador and followed up five years later.
The researchers identified several factors that might influence risk of developing asthma, such as exposure to antibiotics, having respiratory infections, and whether or not the infants were breastfed. Of the 29 infants in the high-risk asthma group, more than 50 percent had asthma by age 5, Finlay said.
Surprisingly, the strongest predictor of whether a child developed asthma wasn’t bacterial. It was the presence of Pichia. And the yeast wasn’t protective; it tipped the scales toward asthma.
Finlay speculated that molecules made by the fungi interact with the infants’ developing immune systems in a way that somehow increases asthma risk. It isn’t clear how the infants’ guts acquire the fungus; some species of Pichia are found in soil, others in raw milk and cheese. Finlay and his colleagues are now going to look for the fungus in Canadian children’s gut microbes..
The researchers also looked at other gut microbe‒related factors that upped the Ecuadorean children’s asthma risk. Children with access to clean water had higher asthma rates, Finlay said. While drinking clean water helps people avoid several ills such as cholera, the link to asthma highlights how some dirt can be protective, he said. “We’ve cleaned up our world too much.” This research underscores that caution should be used when generalizing about our intestinal flora. “What’s emerging is that it is very personalized,” gastroenterologist Eran Elinav of the Weizmann Institute of Science in Rehovot, Israel, said at the news conference. For example, evidence implicates some fungi in the development of inflammatory bowel disease, Elinav said, but it depends on the individual.
Scientists have constructed five more yeast chromosomes from scratch. The new work, reported online March 9 in Science, brings researchers closer to completely lab-built yeast.
“We’re doing it primarily to learn a little more about how cells are wired,” says geneticist Jef Boeke of the New York University Langone Medical Center. But scientists might also be able to tinker with a synthetic yeast cell more efficiently than a natural one, allowing more precise engineering of everything from antiviral drugs to biofuels. Boeke was part of a team that reported the first synthetic yeast chromosome in 2014 (SN: 5/3/14, p. 7). Now, several hundred scientists in five countries are working to make all 16 Saccharomyces cerevisiae yeast chromosomes and integrate them into living cells. With six chromosomes finished, Boeke hopes the remaining 10 will be built by the end of 2017.
Each synthetic chromosome is based on one of S. cerevisiae’s, but with tweaks for efficiency. Researchers cut out stretches of DNA that can jump around and cause mutations, as well as parts that code for the same information multiple times.
When the researchers put chunks of synthetic DNA into yeast cells, the cells swapped out parts of their original DNA for the matching engineered snippets.
Yeast is a eukaryote — it stores its DNA in a nucleus, like human cells do. Eventually, this research could produce synthetic chromosomes for more complicated organisms, Boeke says, but such feats are still far in the future.
NEW ORLEANS — The tiniest electronic gadgets have nothing on a new data-storage device. Each bit is encoded using the magnetic field of a single atom — making for extremely compact data storage, although researchers have stored only two bits of data so far.
“If you can make your bit smaller, you can store more information,” physicist Fabian Natterer of the École Polytechnique Fédérale de Lausanne in Switzerland said March 16 at a meeting of the American Physical Society. Natterer and colleagues also reported the result in the March 9 Nature. Natterer and colleagues created the minuscule magnetic bits using atoms of holmium deposited on a surface of magnesium oxide. The direction of each atom’s magnetic field served as the 1 or 0 of a bit, depending on whether its north pole was pointing up or down.
Using a scanning tunneling microscope, the scientists could flip an atom’s magnetic orientation to switch a bit from 0 to 1. To read out the data, the researchers measured the current running through the atom, which depends on the magnetic field’s orientation. To ensure that the change in current observed after flipping a bit was due to a reorientation of the atom’s magnetic field, the team added bystander iron atoms to the mix and measured how the holmium atoms’ magnetic fields affected the iron atoms.
The work could lead to new hard drives that store data at much greater densities than currently possible. Today’s technologies require 10,000 atoms or more to store a single bit of information.
Natterer also hopes to use these mini magnets to construct materials with fine-tuned magnetic properties, building substances a single atom at a time. “You can play with them. It’s like Lego,” he says.
Glass frogs often start life with some tender care from a source scientists didn’t expect: frog moms.
Maternal care wouldn’t be news among mammals or birds, but amphibian parenting intrigues biologists because dads are about as likely as moms to evolve as the caregiver sex. And among New World glass frogs (Centrolenidae), what little parental care there is almost always is dad’s job — or so scientists thought, says Jesse Delia of Boston University. Months of strenuous nights searching streamside leaves in five countries, however, have revealed a widespread world of brief, but important, female care in glass frogs. In examining 40 species, Delia and Laura Bravo-Valencia, now at Corantioquia, a government environmental agency in Santa Fe de Antioquia, Colombia, found that often mothers lingered over newly laid eggs for several hours. By pressing maternal bellies against the brood, moms hydrated the jelly-glop of eggs and improved offspring chances of survival, Delia, Bravo-Valencia and Karen Warkentin, also of BU, report online March 31 in the Journal of Evolutionary Biology.
Glass frogs take their name from see-through skin on their bellies and, in certain cases, transparent organ tissues. (Some have clear hearts that reveal blood swishing through.) These frogs aren’t exactly obscure species, but until this field project, which stretched over six rainy seasons, female care in the family was unknown.
Female glass frogs may not cuddle their eggs for long, but it’s enough to matter, the researchers found. As is common in frogs, the mothers don’t drink with their mouths but absorb water directly through belly skin into a bladder. Moms pressing against a mass of newly laid eggs caused the protective goo to swell — perhaps by osmosis or peeing — and the mass to quadruple in size. For some of the glass frogs in the study, the youngsters were on their own once mom left. But at least hydration created an unpleasant amount of slime for a predator to bite through before getting to frog embryos. Night-hunting katydids in captivity, when offered a choice, barely nibbled at a hydrated mass of frog offspring, concentrating instead on eating an unhydrated clutch. In the field, when researchers removed about two dozen moms from their clutches in two species, mortality at least doubled to around 80 percent. Predators and dehydration caused the most deaths.
There are still more than 100 glass frog species that Delia and Bravo-Valencia haven’t yet watched in the wild. But the researchers did track down maternal care in 10 of 12 genera. Such a widespread form of maternal care probably evolved in the ancestor of all glass frogs, the researchers propose after analyzing glass frog family trees several ways.
In contrast, prolonged care from glass frog dads — rehydrating the egg mass as needed and fighting off predators such as hungry spiders — seems to have arisen independently later, at least twice. Across evolution in the animal kingdom, “usually we don’t see transitions from female to male care,” Delia says. “The pattern we found is completely bizarre.”
Why females started hanging around their eggs at all fascinates Hope Klug, an evolutionary biologist at the University of Tennessee at Chattanooga who studies parental care. In frogs, with eggs mostly fertilized externally, females could easily leave any care to dad.
“Parental care is perhaps more common and diverse in animals than we realize,” she says. “We just might have to look a little bit harder for it.”
Got a mouse in the house? Blame yourself. Not your housekeeping, but your species. Humans never intended to live a mouse-friendly life. But as we moved into a settled life, some animals — including a few unassuming mice — settled in, too. In the process, their species prospered — and took over the world.
The rise and fall of the house mouse’s fortunes followed the stability and instability of the earliest human settlements, a new study shows. By analyzing teeth from ancient mice and comparing the results to modern rodents hanging out near partially settled groups, scientists show that when humans began to settle down, one mouse species seemed to follow. When those people moved on, another species moved in. The findings reveal that human settlement took place long before agriculture began, and that vermin didn’t require a big storehouse of grain to thrive off of us.
Between 15,000 and 11,000 years ago (a time called the Natufian period), people began to form small stone settlements in what is now Israel and Jordan. They were not yet farming or storing grain, but they were living in a single place for a season or two, and coming back to that place relatively often. Those early settlers changed the ecosystem of the world around them — presenting new opportunities for local flora and fauna.
Lior Weissbrod, an archaeologist at the University of Haifa in Israel, started his career wanting to search for clues to the history of animal-human relationships. He was especially interested in animal remains. But, he admits, mouse teeth weren’t exactly his first choice. “[At] the site I was going to work on, the remains of larger animals were already studied,” he says. “I was left with the small mammals.”
Small mammals have even smaller teeth. The largest mouse molars are only about 1 millimeter long. This meant a lot of time sifting dirt through very fine mesh for Weissbrod. He collected 372 mouse teeth from the dirt of five different archaeological sites in modern-day Israel and Jordan, with remains dating from 11,000 to 200,000 years ago. He gave the teeth to his colleague Thomas Cucchi of the National Museum of Natural History in Paris, who developed a technique to classify the mouse teeth by species based on tiny differences in their shape. The first human settlements were only a few houses, but that’s a seismic shift if you’re the size of a mouse. Before the settlements were built, the mouse species Mus macedonicus scurried through the undergrowth. But after stone buildings arrived, another species dominated — Mus domesticu s. When humans left the settlements for about 1,000 years around 12,000 years ago, the reverse occurred: M. domesticus left and M. macedonicus moved back in. The two species probably competed against each other when humans were absent, Weissbrod hypothesizes. But when people were around, M. domesticus was better at taking advantage of human presence. They may have had more flexible diets — making it easier to live off our leavings — and less fear of people. “Once you get humans into the picture and human settlements … there’s a creation of a new habitat,” he explains. “This species [M. domesticus] is finally getting a break from the competition.”
Ancient samples alone would not be enough to establish whether one mouse species could out-compete another based on human settlement alone. For a modern approximation of the ancient, partially settled lifestyle, Weissbrod turned to the Maasai, a nomadic cattle-herding group in southern Kenya. “Maasai are nothing like ancient hunter-gatherers,” he notes. “But we look at specific things that make them comparable.” Maasai herders tend to live in small groups, and use those settlements over and over. “The Maasai aren’t sedentary, they are on the verge perhaps,” he explains. “So they move [often] but not to the extent of highly mobile nomadic groups, they move on a seasonal basis.”
Weissbrod headed to Kenya to collect 192 live, spiny mice, living around Maasai settlements. These mice could be divided into two species, Acomys wilsoni — the short-tailed version — and Acomys ignitus, with longer tails. An archaeologist used to working with dry and dusty fossils, Weissbrod had to adjust to working with live, wiggling rodents. “It took a conscious process of pushing myself to get over the ingrained aversion,” he says. Like their ancient kin, one modern spiny mouse had a competitive advantage when people were present. A. ignites made up 87 percent of the mice caught hanging out with the Maasai, but only 45 percent of the mice in non-settled area. The associations between mice and men allowed Weissbrod, Cucchi and their colleagues to show how house mice came to live alongside us — no grain or farming required. “We can show with a high degree of certainty now that mice became attached to us 3,000 years before farming,” Weissbrod says. “From that we learned hunter-gatherers were making the transition to sedentary lives before farming. They didn’t need the crops to make that transition.” Weissbrod and his colleagues published their findings March 27 in the Proceedings of the National Academy of Sciences.
“I thought it was wonderful,” Melinda Zeder, an archaeologist at the Smithsonian Institution in Washington, D.C., says of the study. “I really appreciated it on a number of levels.” Zeder said she was impressed that such a big finding could come from samples so incredibly small. “It’s not a keystone or early writing, it’s something most people overlook,” she says. “Out of the mouths of mice, we’re getting a wonderful view of a pivotal time in history.”
Other species certainly took advantage of human settlement, Zeder notes. Wolves and wild boar arrived and “auditioned themselves for a starring role as a domesticate.” A few of the friendlier ones began to interact more with people. Those people began to see the advantages of the animals. From wolves were born dogs, and from wild boar our pigs.
But when humans weren’t paying attention, other species moved in and thrived on their own. Mice aren’t the only vermin that have arrived to, as Weissbrod says, “domesticate themselves.” Sparrows, pigeons, rats and other species have come to take advantage of our presence. We may have never seen a use for them, but that doesn’t stop them from using us.
The juice saga continues. The American Academy of Pediatrics updated their official ruling on fruit juice, recommending none of the sweet stuff before age 1. Published in the June Pediatrics, the recommendation is more restrictive than the previous one, which advised no juice before age 6 months.
The move comes from the recognition that whole fruits — not just the sweet, fiberless liquid contained within — are the most nutritious form of the food. Babies under 1 year old should be getting breast milk or formula until they’re ready to try solid foods. After their first birthdays, any extra liquids they drink should be water or milk. (These updated guidelines may not apply to babies who might need fruit juice to help with constipation.)
Whole fruits — or, mashed up clumps of them — have more fiber and protein than juice. The only benefit that juice has over its former whole form is that it’s way easier for a kid to slurp down.
The potential risks of cavities and obesity in part prompted the updated guidelines. It’s worth saying that neither of these outcomes are guaranteed with juice drinking. In fact, a recent study failed to find a link between juice drinking and excessive weight gain in children. Still, juice offers no nutritional advantage over whole fruits, so the reasoning of the AAP seems to be, “Why risk it?”
The AAP gave additional, more nuanced advice for parents who do decide to give juice to children age 1 and older:
Don’t give kids juice in bottles or sippy cups, especially at bedtime. That ease of drinkability would encourage kids to drink juice for long periods of time, prolonging sugar baths for teeth.
Look out for unpasteurized juice. Harmful forms of E. coli bacteria can appear in unpasteurized apple cider, for instance, posing a particular risk for young people.
Give 1- to 3-year-old kids no more than 4 ounces of juice a day. That recommendation drops 2 ounces from earlier guidance that limited juice to between 4 and 6 ounces daily. Children ages 4 to 6 years old get those extra 2 ounces back, with a daily limit of between 4 and 6 ounces.
Make sure kids are drinking 100 percent juice, not those sneaky “cocktails” or “drinks.” Those are often nutritional wastelands, packed with even more sugar and devoid of other nutrients. Though the guidelines don’t mention habit formation, I suspect this also came into play in the AAP’s encouragement of whole fruits over juice. Children’s taste preferences get shaped early. Really early, actually. Fetuses learn to love flavors their mothers ate while pregnant. So babies who grow accustomed to sweet juice might be less impressed with water or milk. And while that might not be a problem in the early years of life, years or decades of drinking sweet liquids will catch up with them eventually.
Anyone who’s dragged roller luggage knows it’s liable to fishtail. To most people, this is a nuisance. To a few scientists, it’s a physics problem. Researchers detail the precise interplay of forces that set suitcases shimmying in a study published online June 21 in Proceedings of the Royal Society A.
The researchers simulated and observed the motion of a toy model suitcase on a treadmill. They found that the suitcase’s side-to-side motion at any given moment is related to its tilt and distance off-center from the line of travel. For instance, imagine a suitcase rolling straight ahead, but then hitting a bump or cutting a corner that causes the right wheel to lift. The suitcase’s tilt makes the left wheel steer the suitcase rightward. When the right wheel falls back to the ground and the left wheel lifts off, the suitcase — now positioned and tilted to the right — banks left. Switch wheels, swing, repeat.
“It’s a pretty good analysis of the system,” says Andy Ruina, a physicist at Cornell University who was not involved in the research.
This swaying motion is “a bit funny and counterintuitive,” says study coauthor Sylvain Courrech du Pont. It actually gets smaller when the suitcase rolls faster. Lowering the angle of the suitcase can get the rocking to stop altogether, he says.
Understanding the physics of this system could be useful for more than designing stable suitcases, because it also applies to other two-wheel carriers — like car-pulled trailers. “In the near future, maybe we will have a car without a driver,” says Courrech du Pont, a physicist at Paris Diderot University. “It would be a good thing if the car knows how to stop this kind of motion.”
When it comes to smelling pretty, petunias are pretty pushy.
Instead of just letting scent compounds waft into the air, the plants use a particular molecule called a transporter protein to help move the compounds along, a new study found. The results, published June 30 in Science, could help researchers genetically engineer many kinds of plants both to attract pollinators and to repel pests and plant eaters.
“These researchers have been pursuing this transporter protein for a while,” says David Clark, an expert in horticultural biotechnology and genetics at the University of Florida in Gainesville. “Now they’ve got it. And the implications could be big.” Plants use scents to communicate (SN: 7/27/02, p. 56). The scent compounds can attract insects and other organisms that spread pollen and help plants reproduce, or can repel pests and plant-eating animals. The proteins found in the new study could be used to dial the amount of scent up or down so that plants can attract more pollinators or better protect themselves. Currently unscented plants could be engineered to smell, too, giving them a better shot at reproduction and survival, Clark says. Plants get their scents from volatile organic compounds, which easily turn into gases at ambient temperatures. Petunias get their sweet smell from a mix of benzaldehyde, the same compound that gives cherries and almonds their fruity, nutty scent, and phenylpropanoids, often used in perfumes.
But nice smells have a trade-off: If these volatile compounds build up inside a plant, they can damage the plant’s cells. About two years ago, study coauthor Joshua Widhalm, a horticulturist at Purdue University in West Lafayette, Ind., and colleagues used computer simulations to look at the way petunias’ scent compounds moved. The results showed that the compounds can’t move out of cells fast enough on their own to avoid damaging the plant. So the researchers hypothesized that something must be shuttling the compounds out.
In the new study, led by Purdue biochemist Natalia Dudareva, the team looked for genetic changes as the plant developed from its budding stage, which had the lowest levels of volatile organic compounds, to its flower-opening stage, with the highest levels. As flowers opened and scent levels peaked, the gene PhABCG1 went into overdrive; levels of the protein that it makes jumped to more than 100 times higher than during the budding stage, the researchers report.
The team then genetically engineered petunias to produce 70 to 80 percent less of the PhABCG1 protein. Compared with regular petunias, the engineered ones released around half as much of the scent compounds, with levels inside the plant’s cells building to double or more the normal levels. Images of the cells show that the accumulation led to deterioration of cell membranes.
A lot of work has been done to identify the genes and proteins that generate scent compounds, says Clark. But this appears to be the first study to have identified a transporter protein to shuttle those compounds out of the cell. “That’s a big deal,” he says.
Humpback whales, those innovative foodies, have discovered their own pop-up restaurants.
Migrant humpbacks returning to southeastern Alaska in spring are the first of their kind known to make routine visits to fish hatcheries releasing young salmon into the sea, says marine ecologist Ellen Chenoweth.
The whales are “40 feet long and they’re feeding on fish that are the size of my finger,” says Chenoweth, of the Juneau fisheries center of University of Alaska Fairbanks. For tiny prey to be worthwhile to humpbacks, it’s good to find crowds — such as young salmon streaming out of hatchery nets.
Six years of systematic observations of whales at five hatcheries at Baranof Island reveal a pattern of humpbacks visiting during springtime releases, Chenoweth and her colleagues report June 12 in Royal Society Open Science.
Whale visits to the salmon buffet enhance humpbacks’ reputation for innovation in feeding, Chenoweth says. And since the water is relatively shallow, visits also make it easier to film humpback lunge feeding. More often, studying whale food dives means watching animals surface from the depths to catch their breath before the next exciting plunge. “It’s like going to a basketball game but you can only really watch players on the bench,” Chenoweth says.
Underwater, a humpback opens its jaws and rushes into the mass of prey as its throat balloons out “like a parachute opening,” she says. The toothless whale then filters the mouthful, swooshing it out through dangling fringes of baleen, which snag what’s worth swallowing. In one lunge, a humpback can take in about 27,600 liters of seawater — about 28 metric tons — roughly doubling the whale’s weight.
