Scientists may work to prevent bias, but they don’t always say so

For a scientist, conducting a scientific study is walking into a minefield of potential biases that could detonate all over the results. Are the mice in the study randomly distributed among treatment groups? Does the person evaluating an animal’s behavior know what treatment the mouse got — and thus have an expectation for the outcome? Are there enough subjects in each group to reduce the odds that the results are due to chance?

“I think we’re getting increasingly better at identifying these risks and identifying clever and practical solutions,” says Hanno Würbel, an applied ethologist at the University of Bern in Switzerland. “But it’s not all obvious, and if you look back at the history of science you find that these methods have accumulated through a learning process.”

In theory, every time scientists design an experiment, they keep an eye out for these and other potential sources of bias. Then, when scientists submit the study design for approval or write journal articles about the work, they share that research design with their colleagues.

But scientists may be leaving some rather key bits out of their reports. Few animal research applications and published research reports include specific mentions of key factors used to eliminate bias in research studies, Würbel and colleagues Lucile Vogt, Thomas Reichlin and Christina Nathues report December 2 in PLOS Biology. The results suggest that the officials who approve animal research studies — and the scientists who peer review studies before publication — are trusting that researchers have accounted for potential biases, whether or not there is evidence to support that trust.

The team gained access to 1,277 applications for animal experiments submitted to the Swiss government in 2008, 2010 and 2012. The researchers examined the applications for seven common measures used to prevent bias: Randomization, calculations to make sure sample sizes were large enough, not telling the experimenter what treatment will be administered to the next animal, blinding the experimenter during testing to which animals received which treatment, criteria used to include or exclude subjects (say, the animal’s age or sex), explicitly stating the primary outcome to be measured and plans for statistical analysis of the data.

Most of the time, the applications didn’t mention how or whether any of those measures were considered. Scientists included statistical plans 2.4 percent of the time and sample size calculations only 8 percent of the time. Even the primary outcome variable — the main objective measured in the study — was mentioned in only 18.5 percent of the applications.

Würbel’s group also looked at 50 publications that came out of some of those animal research applications that were ultimately approved. Here, scientists were better about reporting their effort to stave off bias in their studies. If scientists mentioned one of the seven efforts to combat bias in their animal experiment applications, they were more likely to mention it when their final papers were published. But they still only reported the statistical plan 34 percent of the time, and none of the 50 papers reported sample size calculations.
Switzerland’s animal research application process didn’t actually require that any of these measures of bias be disclosed, Würbel notes. But “unless [the licensing officials] know the studies have been designed rigorously, they can’t assess the benefit.” The implication, the researchers suggest, is that authorities approving the studies trusted that the scientists knew what they were doing, and that peer reviewers and editors trusted that the authors of journal articles took those forms of bias into account.

Was that trust well placed? To find out, Reichlin, Vogt and Würbel surveyed 302 Swiss scientists who do experiments on living organisms, asking about the efforts they made to combat bias, and how often they reported those efforts. When asked directly, scientists said that of course they control their studies for certain risks of bias. The vast majority — 90 percent — reported that they included the primary outcome variable, and 82 percent included a statistical analysis plan. A full 69 percent reported that they calculated their sample sizes. Most also reported that they wrote these antibias efforts into their latest published research article.

But when the team probed deeper, asking scientists specific questions about what methods they used to combat bias, “you find out they don’t know much about methods,” Würbel notes. Only about 44 percent of the researchers knew about the guidelines for how to report animal experiments, even though 51 percent of them had published in a journal that endorsed those guidelines, the researchers report December 2 in PLOS ONE.

“This is a type of empirical work that we need, to see how people think and what they do,” says John Ioannidis, a methods researcher at Stanford University in California.

Just because scientists aren’t reporting certain calculations or plans doesn’t mean that their research will be subject to those biases. But without efforts to rigorously prevent bias, it can sneak in — subjects that aren’t randomly assigned properly, or an experimenter who unconsciously leans toward one result or another. Too small of a sample size and a researcher could detect a difference that disappears in a larger group. If a researcher knows which animals got which treatment, they may unconsciously focus more carefully on some aspects of the treated animals’ behavior — ignoring similar behavior in the control. And that can result in studies that are tougher to replicate — or that can’t be replicated at all.

None of this means that scientists are ill-educated or performing science badly, notes Malcolm Macleod, a neurologist at the University of Edinburgh. “I think there’s a temptation to make this binary, [to say] people don’t know so we need to train them,” he says. “The fact is most scientists know a bit … [but] everyone has something they can do better.”

How do you make scientists take more actions against bias, and then report what they’ve done? Journals, funding bodies and agencies approving animal research projects could require more information of scientists. Journals could require checklists for reporting methods, for example. Journals or funding bodies could also require full preregistration of animal studies, where a scientist gives all the details of a study and how it will be analyzed before the experiments are ever performed. (Such pre-registration became mandatory for clinical studies in humans in the United States in 2000.) Detailed reporting isn’t complete insurance against an irreproducible result, but “the more information you have, the easier it is to reproduce,” says Vogt, who studies animal welfare at the University of Bern.

Some scientists might worry that preregistration is too onerous, or that it could straitjacket researchers into unproductive studies. It would be frustrating, after all, to be stuck with a hypothesis that is clearly not bearing out, when the data provide tantalizing hints of another path to pursue. But it’s possible to provide the flexibility to pursue interesting questions, while still making sure the studies are rigorous, Ioannidis says.

But when scientists don’t know sources of bias in the first place, more education might be a good place to start. “When I first came into the lab for my master’s thesis, I had a lot of information [about research design] but I wasn’t ready to apply it,” Vogt explains. “I needed guidance through the steps of how to plan an experiment, and how to plan to report the experiment afterward.” Education doesn’t stop when graduate students leave the classroom, and more continuing education might help scientists — students and emeriti alike — recognize unfamiliar sources of bias and provide tools to combat it.

Scientists move closer to building synthetic yeast from scratch

Synthetic yeast is on the rise.

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.

Single-atom magnets store bits of data

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.

For glass frogs, moms matter after all

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.”

How the house mouse tamed itself

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.

Sea creatures’ sticky ‘mucus houses’ catch ocean carbon really fast

Never underestimate the value of a disposable mucus house.

Filmy, see-through envelopes of mucus, called “houses,” get discarded daily by the largest of the sea creatures that exude them. The old houses, often more than a meter across, sink toward the ocean bottom carrying with them plankton and other biological tidbits snagged in their goo.

Now, scientists have finally caught the biggest of these soft and fragile houses in action, filtering particles out of seawater for the animal to eat. The observations, courtesy of a new deepwater laser-and-camera system, could start to clarify a missing piece of biological roles in sequestering carbon in the deep ocean, researchers say May 3 in Science Advances.
The houses come from sea animals called larvaceans, not exactly a household name. Their bodies are diaphanous commas afloat in the oceans: a blob of a head attached to a long tail that swishes water through its house. From millimeter-scale dots in surface waters to relative giants in the depths, larvaceans have jellyfish-translucent bodies but a cordlike structure (called a notochord) reminiscent of very ancient ancestors of vertebrates. “They’re more closely related to us than to jellyfish,” says bioengineer Kakani Katija of the Monterey Bay Aquarium Research Institute in Moss Landing, Calif.

The giants among larvaceans, with bodies in the size range of candy bars, don’t form their larger, enveloping houses when brought into the lab. So Katija and colleagues took a standard engineering strategy of tracking particle movement to measure flow rates in fluids and reengineered equipment to watch giant houses at work deep in the ocean.
Getting the hardware right was challenging, and so was deploying it remotely from a research ship at the surface of the Monterey Bay. “This is a 1-millimeter-thick laser sheet bisecting an animal that’s about 2 centimeters wide that is 400 meters below the surface vessel,” Katija says.
The rig managed to capture measurements of water flow through houses of larvaceans belonging to two Bathochordaeus species. The top rate for B. mcnutti, more than 20 milliliters per second, broke the record (previously held by salps) for fastest recorded filtration rates from a zooplankton. If the maximum population of giant larvaceans in Monterey Bay pumped water that fast, they would clean all the particles out of their home depth in about 13 days.
Larvacean feeding rates matter because the sea creatures send organic matter, including carbon, to the deep ocean in two ways, explains biological oceanographer Stephanie Wilson of Bangor University in Wales. Larvaceans discard houses that become clogged with particles pumped in. (Small species can secrete a replacement in minutes though giants take longer. “Imagine that you have a head full of snot, and you sneeze your house,” Wilson says.)

Larvaceans also send carbon to the seafloor in football-shaped excrement. That’s an American football, Wilson clarifies. The tiny plankton that larvaceans near the surface eat wouldn’t sink far on their own, but once an animal ingests them and excretes a dense pellet, the carbon in the meal sinks better.

If carbon-containing fallout from the upper ocean falls fast enough, it bypasses diversions by other creatures and reaches depths where nothing much happens to it for a long time, says Sari Giering of the National Oceanography Centre in Southampton, England, where she studies oceanic carbon. “The faster a particle sinks, the more likely its carbon will be stored in the ocean for centuries,” she says.

Giering enthusiastically welcomes the new laser-and-camera system. She points out that researchers thought giant larvaceans could be important in sequestering carbon. But the fragile houses have been hard to study in action until now.

Toddlers’ screen time linked to speech delays and lost sleep, but questions remain

One of the most pressing and perplexing questions parents have to answer is what to do about screen time for little ones. Even scientists and doctors are stumped. That’s because no one knows how digital media such as smartphones, iPads and other screens affect children.

The American Academy of Pediatrics recently put out guidelines, but that advice was based on a frustratingly slim body of scientific evidence, as I’ve covered. Scientists are just scratching the surface of how screen time might influence growing bodies and minds. Two recent studies point out how hard these answers are to get. But the studies also hint that the answers might be important.

In the first study, Julia Ma at the University of Toronto and colleagues found that, in children younger than 2, the more time spent with a handheld screen, such as a smartphone or tablet, the more likely the child was to show signs of a speech delay. Ma presented the work May 6 at the 2017 Pediatric Academic Societies Meeting in San Francisco.

The team used information gleaned from nearly 900 children’s 18-month checkups. Parents answered a questionnaire about their child’s mobile media use and then filled out a checklist designed to identify heightened risk of speech problems. This checklist is a screening tool that picks up potential signs of trouble; it doesn’t offer a diagnosis of a language delay, points out study coauthor Catherine Birken, a pediatrician at The Hospital for Sick Children in Toronto.

Going into the study, the researchers didn’t have expectations about how many of these toddlers were using handheld screens. “We had very little clues, because there is almost no literature on the topic,” Birken says. “There’s just really not a lot there.”

It turns out that about 1 in 5 of the toddlers used handheld screens, and those kids had an average daily usage of about a half hour. Handheld screen time was associated with potential delays in expressive language, the team found. For every half hour of mobile media use, a child’s risk of language delay increased by about 50 percent.

“The relationship is not that strong,” Birken says, and those numbers come with big variations. Still, a link exists. And finding that association means there’s a lot more work to do, Birken says. In this study, researchers looked only at time spent with handheld screens. Future studies could investigate whether parents watching along with a child, the type of content or even time of day might change the calculation.

A different study, published April 13 in Scientific Reports, looked at handheld digital device use among young children and its relationship to sleep. As a group, kids from ages 6 months to 3 years who spent more time using mobile touch screen devices got less sleep at night.
Parent surveys filled out online indicated that each hour of touch screen use was linked to 26.4 fewer minutes of night sleep and 10.8 minutes more sleep during the day. Extra napping time “may go some way to offset the disturbed nighttime sleep, but the total sleep time of high users is still less than low users,” says study coauthor Tim Smith, a cognitive psychologist at Birkbeck, University of London. Each additional hour of touch screen use is linked to about 15 minutes less sleep over 24 hours.

By analyzing 20 independent studies, an earlier study found a similar link between portable screen use and less sleep among older children. The new results offer “a consistent message that the findings from older children translate into those younger,” says Ben Carter of King’s College London, who was a coauthor on the study of older children.

So the numbers are in. Daily doses of Daniel Tiger’s Neighborhood on a mobile device equals 7.5 minutes less sleep and a 50 percent greater risk of expressive language delay for your toddler, right? Well, no. It’s tempting to grab onto these numbers, but the science is too preliminary. In both cases, the results show that the two things go together, not that one caused the other.

It may be a long time before scientists have answers about how digital technology affects children. In the meantime, you can follow the American Academy of Pediatrics’ recently updated guidelines, which discourage screens (except for video chatting) before 18 months of age and for all children during meals or in bedrooms.

We now live in a world where smartphones are ever-present companions, a saturation that normalizes the sight of small screens in tiny hands. But I think we should give that new norm some extra scrutiny. The role of mobile devices in our kids’ lives — and our own — is something worth thinking about, hard.

It’s best if babies don’t drink their fruit as juice

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.

Here’s why your wheelie suitcase wobbles

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.”

Petunias spread their scent using pushy proteins

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.