BALTIMORE — When it comes to swimming sperm, it’s not every man for himself. Instead, sperm form groups that swim together, a bit like schools of fish or flocks of birds, physicists have observed.
Understanding the physics underlying such behavior in animals is difficult because their actions arise in part from cognitive processes — birds, for instance, can see what their neighbors are doing and adjust their flight path accordingly. But with sperm, group swimming emerges from the physics of the medium in which they swim, Chih-Kuan Tung of North Carolina A&T State University in Greensboro said in a news conference March 16 at a meeting of the American Physical Society. That makes sperm a simpler system for studying the physics behind a form of coordinated biological action. “They don’t think,” Tung said. “So whatever interaction is happening, we can quantitatively describe it.”
Sperm don’t form groups in ordinary water, Tung said, but they do in viscoelastic fluids such as the mucus of mammalian reproductive tracts. A viscoelastic fluid combines resistance to flow with the ability to restore its previous state when disturbed. Tung and colleagues created such elasticity by adding a polymer to the fluid used for testing the swimming ability of bulls’ sperm. Those experiments showed that it’s the elasticity, not the viscosity, that encourages collective swimming.
Further work will be needed, Tung said, to determine whether such group swimming confers an advantage to sperm seeking an egg. In any event, the new understanding of sperm dynamics could lead to improved methods for in vitro fertilization procedures, he said.
Neither a giant asteroid nor a gradual die out can take full blame for dinosaurs’ demise.
Rather, the culprit may be both, two new studies suggest.
Tens of millions of years before the asteroid delivered its killer blow some 66 million years ago, the number of dinosaur species had already begun to drop, researchers report online April 18 in the Proceedings of the National Academy of Sciences. But not all dino groups were in decline, including some maniraptoran dinosaurs, a different group of researchers suggests online April 21 in Current Biology. At first glance, the two studies seem to conflict, but “they can coexist,” says paleontologist Michael Benton, who coauthored the PNAS paper. Both studies add to what has become an increasingly intricate picture of dinosaurs’ final days.
“Things are a wee bit more complicated than we used to think,” says Benton, of the University of Bristol in England.
In the 1960s and ‘70s, scientists generally believed that dinosaurs petered out after a long, gradual decline. That view took a U-turn in 1980, when researchers proposed that, instead, an asteroid impact might have suddenly triggered the extinction. “The flip-flop was quite extreme,” Benton says of the changed thinking. “Dinosaurs went from long-term decline to instant death.”
What actually happened, he says, is probably more nuanced. Benton and colleagues analyzed the number of dinosaur species emerging and going extinct over a huge timescale: roughly 175 million years. Around 40 million to 50 million years before the mass extinction, dinosaurs started losing species faster than they were gaining new ones, the researchers found. This loss in diversity could have made it harder for dinosaurs to bounce back from the asteroid’s catastrophic impact.
“This doesn’t in any way attack the importance of the impact,” Benton says. But across the board, he says, dinosaur species numbers were dwindling. At least two groups, however, seemed to buck the trend. Hadrosaurs (duck-billed dinosaurs) and ceratopsids (the group that includes Triceratops) were booming up until the end, the team found. According to the Current Biology analysis, toothed maniraptorans (small birdlike relatives of velociraptors) were thriving, too. A detailed examination of more than 3,000 of these dinosaurs’ teeth suggests that these dinos’ ecosystem was pretty stable millions of years before the extinction, says study coauthor Derek Larson, a paleontologist at the Philip J. Currie Dinosaur Museum in Alberta and the University of Toronto.
Larson and colleagues looked for variations in the teeth’s dimensions, and the size of tooth serrations. Then they determined how much that variation changed over time. Big changes could be a hint that these dinos were on the decline, Larson says. But instead, “things basically stayed the same through the last 18 million years of the Cretaceous,” he says.
Toothed maniraptorans “seemed to be doing just fine right up until the extinction,” says University of Oxford paleobiologist Roger Benson, who was not involved in either study.
Larson’s team wondered why the toothed, meat-eating maniraptorans went extinct after the impact while their relatives — the beaked ancestors of modern birds — didn’t. The answer could be dietary, the researchers propose. They analyzed the diets of modern birds to try and figure out what an ancestral bird might have eaten. It probably relied on seeds, Larson says, a hardy food source that could have lasted for decades.
Seeds might have sustained ancient birds through a “nuclear winter,” the debris-darkened skies that could have blotted out the sun following an asteroid impact. When hoards of plants and animal species died out, and dinosaurs ran out of food, he says, “the only resource that would have been reliable and available would have been seeds.”
Not all cosmic mysteries lie light-years away. Some secrets are being unearthed on our nearest neighbor, about a quarter of a million miles from home.
For almost seven years, NASA’s Lunar Reconnaissance Orbiter has been keeping a close eye on the moon. During its tenure, the spacecraft has cataloged craters, pinpointed subsurface deposits of water ice and found evidence of recent volcanic activity. It has even witnessed crashes by three other spacecraft. (One, LCROSS, launched a plume of ejecta from the south pole that scientists searched for water vapor.) “No other mission has orbited the moon for as long as LRO has,” says Noah Petro, a geologist at NASA’s Goddard Space Flight Center in Greenbelt, Md. Constant lunar vigilance has “really pushed our understanding of how the moon changes today, over the last billion years and what happened early on.” A July 15 special issue of Icarus celebrates the mission’s many discoveries, which fill out not only the moon’s story, but also reveal how Earth and other rocky planets have been pummeled by space debris over the last 4 billion or so years.
When LRO launched on June 18, 2009, its goals were more modest. The spacecraft was sent to scout landing sites for future astronaut expeditions, hunt for resources such as water and better understand the radiation hazards that human crews would face. Since completing its original one-year assignment, the mission has been extended several times. LRO plans to stay busy through September, and the team has asked NASA for two more years. Water ice turned up in some unexpected places. Other spacecraft had previously seen hints of water, but none could map precisely where it was. Researchers suspected that water lay within permanently shadowed craters at the poles, and LRO did find evidence of ice there. But LRO also found that not all shady spots harbor water, and not all water is found in the shadows — some appears to hide under soil that sits in direct sunlight.
“That was bit of a surprise,” says LRO project scientist John Keller, also at Goddard. Looking at temperature alone, it seems, isn’t enough for understanding the history of water on the moon. In the polar shadows, where temperatures hover around –250° Celsius, water ice can endure for billions of years. But elsewhere, water may have been trapped more recently and protected by the terrain. “There’s an interplay with time, temperature and topography underlying this water story,” says Keller. How the various water deposits are implanted and shuffled about is one enduring puzzle. How small subterraneous pockets stayed warm for so long after the moon formed is another. Lava oozed on the surface in the last 100 million years, judging by smooth, dark terrains that are sparsely cratered. “This flies in the face with what was known about the moon,” Petro says. “We thought lunar volcanism ended about a billion years ago.” Some changes are much more recent. In 2013, Earth-based telescopes detected a flash of light from the moon. LRO checked it out and found a new crater 18 meters across. “What was surprising was how far the ejecta went,” Keller says. Debris had been tossed 35 kilometers — much farther than expected from a space rock estimated to be only about a meter wide.
Understanding what’s currently hitting the moon and the traces those objects leave is crucial to interpreting the history of impacts plastered across the lunar surface; similar impacts also affected Earth but most have been erased by weather and geologic forces. “The moon is our way of studying the history of the Earth since the creation of the Earth-moon system,” Petro says.
One of the seven instruments that LRO carries is a laser altimeter, a beam of light that scans and maps the surface in exquisite detail. “That’s been a game changer,” says Simone Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colo. “We can use the topography data to find old degraded craters that otherwise would not be easily detected in imagery.”
Detailed maps reveal craters on top of other craters, laying out a rough sequence of when things hit the moon. And astronauts have brought back samples from some of these terrains, allowing researchers to use radiogenic dating to figure out when craters formed. That in turn supplies a record of what was smacking into other planets and asteroids. “We have a deep understanding of collisions going back to the beginning of the solar system,” says Marchi. “That can only be done with the moon.”
The females of Stylops ovinae, a parasitic insect species that lives in mining bees, have pretty dull lives. While the males, tiny winged insects, get to flit about — for a few hours, at least, before they die — the females are literally stuck at home, wedged inside a mining bee for their entire lives with only a bit of their cephalothorax (neck) exposed. And worse, once a female’s offspring hatch, they will eat her alive. Oh, and they’ve got no wings, legs, antennae, eyes, mouthparts or genitalia.
How do those offspring come about if the females don’t have genitals? That’s where this female insect’s life gets even more miserable: To get those cannibalistic kids, she has to first undergo traumatic insemination — a mating in which the male pierces her body with his penis.
Mining bees are common in Germany, and sometimes the bees emerge weeks earlier in the spring than expected; these bees have been infected with parasites. Despite how prevalent the bees and their parasites are, figuring out how the parasites reproduce was no easy task. These insects are tiny and their reproductive systems even tinier. The male parasite’s penis, for instance, is only 0.4 millimeters long.
Scientists have bandied about hypotheses of how S. ovinae might reproduce. With no female genitalia and males once thought to be rare, one idea was that the insects employed parthenogenesis to create more insects. Other researchers posited that the bee parasites did have sex but the males used the same brood canal through which offspring emerged to inseminate the female.
Hans Pohl of the Friedrich Schiller University Jena in Germany decided to take a closer look. They brought mining bees into the lab, imaged the bee parasites with a scanning electron microscope, recorded four parasite mating events and did mating experiments to see how often and how long the insects mated. Their results appear April 29 in Scientific Reports.
A male bee parasite, they found, will attach himself to the bee then stick his penis into the female’s body through her neck. He then hangs on for an average of 8 minutes, and as many as 34 minutes, before taking off. Only a few seconds are actually needed to transfer his sperm, so copulating for so long, the researchers say, could be a way to reduce sperm competition with other males.
By bypassing a female’s reproductive tract, traumatic insemination itself is also a way for males to better ensure that their sperm is the stuff that a female uses to make offspring. And the female parasites may have evolved a way to not be too harmed by the act — they have a little pocket of tissue in the neck area in which the male deposits his sperm, and this may provide a little protection from the trauma of multiple males stabbing her in the neck.
Schrödinger’s cat can’t seem to catch a break. The unfortunate imaginary feline is famous for being alive and dead at the same time, as long as it remains hidden inside a box. Scientists have now gone one step further, splitting one living-dead cat between two boxes.
Animal lovers can relax — there are no actual cats involved. Instead, physicists used microwaves to mimic the cat’s weird quantum behavior. The new advance, reported May 26 in Science, brings scientists a step closer to building quantum computers out of such systems. Schrödinger’s cat is the hapless participant in a hypothetical experiment dreamt up by physicist Erwin Schrödinger in 1935. He imagined a cat in a closed box with a lethal poison that will be released if a sample of radioactive material decays. After any given amount of time passes, quantum math can provide only the odds that the material has decayed and released the poison. So from the quantum perspective, the cat is in a state of superposition — both dead and alive. It remains in limbo until the box is opened, and out comes a purring kitty or a lifeless corpse (SN: 11/20/10, p. 15).
In a real laboratory version of the experiment, microwaves inside a superconducting aluminum cavity take the place of the cat. Inside the specially designed cavity, the microwaves’ electric fields can be pointing in two opposing directions at the same time — just as Schrödinger’s cat can be simultaneously alive and dead. These states are known as “cat states.” Now, physicists have created such cat states in two linked cavities, thereby splitting the cat into two “boxes” at once.
Though the idea of one cat in two boxes is “kind of whimsical,” says Chen Wang of Yale University, a coauthor of the paper, it’s not that far off from the real-world situation. The cat state “is shared in two boxes because it’s a global quantum state.” In other words, the cat is not only in one box or the other, but stretches out to occupy both.
Because the states of the two boxes are linked — or in quantum parlance, entangled — if the cat turns out to be alive in one box, it’s also alive in the other (SN: 11/20/10, p. 22). Wang compares it to a cat with two symptoms of life: an open eye in the first box and a heartbeat in the second box. Measurements from the two boxes will always agree on the cat’s status. For microwaves, this means the electric field will always be in sync in both cavities. The scientists measured the cat states produced and found a fidelity of 81 percent — a measure of how close the state was to the ideal cat state. This fidelity is comparable to that achieved in similarly complex systems, the researchers say.
The result is a step toward quantum computing with such devices. The two cavities could serve the purpose of two quantum bits, or qubits. One stumbling block for quantum computers is that errors inevitably slip in to calculations due to interactions with the outside environment that muck up the qubits’ quantum properties. The cat states are more resistant to errors than other types of qubits, the researchers say, so the system could eventually lead to more fault-tolerant quantum computers. “I think they’ve made some really great advances,” says Gerhard Kirchmair of the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences in Innsbruck. “They’ve come up with a very nice architecture to realize quantum computation.”
The demonstration of entanglement in the two-cavity system is very important, says Sergey Polyakov of the National Institute of Standards and Technology in Gaithersburg, Md. “The next step would be to demonstrate that this approach is actually scalable” by adding more cavities to the mix to build a bigger quantum computer.
A sloppy light system may be just what a squid needs to hide from predators. Bioluminescent cells in some glass squid work in a surprisingly inefficient way — leaking a lot of light rather than fully channeling it, a new study suggests.
Glass squid have largely transparent bodies, helpful for inconspicuous swimming in deep open water. Marine predators often scan the waters above them for the telltale silhouettes of prey blocking sunlight, but there’s little to betray a glass squid — except for a few notable features such as the shadow-making eyes on its head. Underneath those eyes, squid in the genus Galiteuthis grow silvery patches of cells that act as undersurface bioluminescence, a camouflage technique that has evolved in various marine creatures, making their shadows less conspicuous to hunters below.
Biophysicist Alison Sweeney of the University of Pennsylvania in Philadelphia had hypothesized that the cells, called photophores, act like microscopic cables that channel the bioluminescent glow of the squid down or out in a specific direction. The skinny, cablelike cells are surrounded by thin, protein-dense layers that create a silver tube that reminds Sweeney of Saran Wrap. But in the first detailed look at these structures, Sweeney and Pennsylvania colleague Amanda Holt found that the channels performed poorly, letting most of the light leak away sideways. That efficiency, it turns out, could be useful, Sweeney and Holt report June 8 in the Journal of the Royal Society Interface. “We always expect that the most ‘perfect’ or efficient mechanism will be the pinnacle of evolution, but this study shows that there are many ways to solve challenges imposed by the environment,” says marine biologist Steven Haddock of Monterey Bay Aquarium Research Institute in California.
Inefficiency might sound like an improbable scenario for success. But, says visual ecologist Justin Marshall of the University of Queensland in Brisbane, Australia, “I believe it.”
Other researchers had discussed the idea that certain sea creatures show a great deal of subtlety in disguising their silhouettes, but Sweeney knew of no other study trying to figure out how supposed cables work. It turns out that the squid structures were “really bad at being fiber-optic cables,” Sweeney says. The cells are about 50 micrometers long, longish for a cell but short for a cable. And the cells couldn’t guide light even over that short distance without losing much of it. Looking at the cross sections of the photophores under a microscope showed big, uneven gaps in the layers. When she first recognized this, she expected to write “a boring paper that’s, ‘Gee, squid cells kind of sort of guide light, but not really.’”
Then came the “of course” moment for Sweeney and her puzzling measurements. “The lesson that keeps coming back to us,” she says, “is that these things are meaningless until you consider the habitat.” After calculating the light environment where wild squid swim, the researchers realized that the overall effect of the leaking tubes created a plausible approximation for the twilightlike haze in which the squid live. A glowing blur might actually make the eyes less conspicuous to predator approaching from a variety of angles.
Irregularities in the sheathing and shapes of the leaky cables might even make the living cables more remarkable, Sweeney speculates. Dividing them into five rough types, the researchers investigated the kinds of light effects each produced and matched those effects with ocean conditions at two locations off Hawaii. If squid can pick which cable doodads to use and when, the animals could improve the match between their under-eye shine and conditions in the ocean.
Other squid with opaque skin flicker, darken and quick-change their tiny color-making structures, she points out. So, the suggestion that eye-glow structures might change, too, “is not crazy,” Sweeney says.
Spoiler alert: Scientists can gauge a film’s emotional tenor from the gasps of its audience. Sure, the audible sounds are a cue, but so are the chemicals exhaled with each sigh and scream. These gases could point the way to a subtle form of human communication.
“There’s an invisible concerto going on,” says Jonathan Williams, an atmospheric chemist at the Max Planck Institute for Chemistry in Mainz, Germany. “You hear the music and see the pictures, but you don’t realize there are chemical signals in the air.” Williams started out measuring the air in a soccer stadium to see if human breath had a noticeable impact on the concentration of greenhouse gases in the atmosphere. The answer was no, at least on a small scale. But he noticed that levels of carbon dioxide and other gases fluctuated wildly whenever the crowd cheered. That got him wondering: Maybe humans’ emissions are influenced by emotions. So he went to the movies.
Williams and colleagues measured air samples collected over six weeks in two movie theaters in Germany. Overall, 9,500 moviegoers watched 16 films — a mix of comedy, romance, action and horror that included The Hunger Games: Catching Fire, Walking With Dinosaurs and Carrie. The researchers classified scenes from the movies using such labels as “suspense,” “laughter” and “crying.” Then they looked for associations between movie scenes and hundreds of compounds in the air.
Certain scenes, primarily those that had people laughing or on the edge of their seats, had distinct chemical fingerprints, the researchers write May 10 in Scientific Reports. During screenings of The Hunger Games: Catching Fire, CO2 and isoprene emissions consistently peaked at two suspenseful moments. Williams and colleagues attribute the spikes in CO2 to increased pulse and breathing rate. The spikes in isoprene — a chemical associated with muscle action — were probably due to tense movie moments.
The researchers had to account for chemicals wafting into the air that may not have been a reaction to onscreen action. People emit chemicals from their perfume, shampoo and even the snacks they munch such as popcorn or beer. During screenings of The Secret Life of Walter Mitty, for instance, the researchers noticed a spike in ethanol corresponding with a scene in which Mitty orders a beer. Williams speculates that the scene reminded movie-goers to take a swig of their own alcoholic beverages.
Scientists need more data to make robust connections between human emotion and chemical emissions. But Williams sees potential practical applications. Marketers, for example, could quickly measure the air during consumer testing to see how people feel about products. He envisions future studies involving heart rate, body temperature and other physiological measurements.
“We have scratched the surface and it’s made a funny smell,” he says. “It’s something to investigate.”
SAN DIEGO — While astrophysicists celebrate the second detection of ripples in spacetime (SN Online: 6/15/16), they are also looking ahead to figuring out what led to these cosmic quakes. Black holes colliding in remote galaxies sent the gravitational waves our way. But how these duos ended up in an ill-fated embrace in the first place is unknown.
With only two clear detections from the Advanced Laser Interferometer Gravitational-Wave Observatory, and a third marginal candidate, there isn’t enough information to figure out for sure how these binary black holes formed. But there are two leading ideas.
One is that two heavyweight stars, each more than roughly 20 times as massive as the sun, are born, live and detonate together. Their deaths would leave behind a pair of black holes snuggled up to one another. They would eventually spiral together in a spectacular collision (SN: 3/19/16, p. 5).
Another idea is that the black holes find each other in the hustle and bustle of a dense star cluster. Within these crowded clusters, stars and black holes gravitationally shove each other around. “My graduate student calls it a black hole mosh pit,” Frederic Rasio, an astrophysicist at Northwestern University in Evanston, Ill., said June 15 during a news briefing at a meeting of the American Astronomical Society.
Rasio and colleagues developed computer simulations that investigate how denizens of these clusters interact with one another. Black holes settle into the center of the cluster, where some get caught in another’s gravitational embrace. Continued run-ins with other wandering black holes fling these pairings from the cluster, leaving the couple to soar across the galaxy and eventually merge into a single black hole.
There’s no way to tell if the two black hole pairs found by LIGO formed as stellar siblings or cluster cousins. But tests could be done as more are found.
Measuring the spins of the black holes could distinguish between formation scenarios, says Rasio. Black holes from previously paired stars will be spinning the same way; those that hooked up in a star cluster are more likely to be spinning in random directions. While LIGO researchers report that one of the black holes in the latest detection was twirling, they can’t tell which one it was or which way its spin axis was pointing. Another test requires finding collisions over a range of distances from Earth. Because it takes time for gravitational waves to reach us, more distant impacts happened earlier in cosmic history. If astronomers notice an uptick in collisions happening around the same time that star formation peaked in the early universe, then pairings of massive stars are the more likely culprit, says Vicky Kalogera, an astrophysicist also at Northwestern.
“This has great potential to tell us how binary black holes formed,” she says. “But we need a larger sample.”
With improved detectors, researchers could eventually listen in on the entire observable universe — and all of cosmic history back to the first wave of star formation. “Big black holes come from big stars,” says Jonah Kanner, a Caltech astrophysicist. And the first stars are thought to have been hundreds of times more massive than our sun. If LIGO had 10 times its current sensitivity, he says, “we could learn about the first generation of stars. That’s exciting astrophysics.”
Such a leap would require a much more ambitious facility, such as a souped-up LIGO with 40-kilometer-long arms, says Kanner (today’s LIGO is one-tenth that size). “That’s the kind of concept where I can daydream,” he says. It’s just a pipedream for now, but over the coming years, new observatories will come online and bring with them incremental improvements in how far researchers can probe.
LIGO itself is undergoing an upgrade, and will be switched back on this fall. The VIRGO detector in Italy should return to service in early 2017 after five-plus years of refurbishment. In Japan, the KAGRA facility is under construction with plans to begin operation in 2018. And the Indian government recently gave the go-ahead to build a third LIGO facility.
“This is just the beginning of gravitational wave astronomy,” said VIRGO spokesperson Fulvio Ricci, a physicist at the Sapienza University of Rome. “We did it, then we did it again, and we will do it again in the future.”
Lightning seen as cause of puzzling chondrules — Lightning flashes in the huge cloud of primeval dust and gas from which the planets in the solar system condensed may have caused formation of the puzzling objects known as chondrules … the tiny, rounded granules about the size of poppy seeds found in stony meteorites…. Dry lightning flashes could have been the source of the fast heating that, followed by quick cooling, [explains] the glassy structure of chondrules. — Science News, July 16, 1966
Update Chondrules are among the oldest pieces of planetary building blocks, formed roughly 4.6 billion years ago during the solar system’s first few million years. How they formed is still up for debate. But the lightning hypothesis has mostly fallen out of favor. One leading idea is that chondrules emerged in the wake of shock waves that rippled through the planet nursery. Those shock waves may have been triggered by collisions of embryonic planets, gas waves spiraling around the sun or strong solar flares.
