Monday, November 29, 2010

Same Face May Look Male or Female, Depending on Where It Appears in a Person's Field of View

Neuroscientists at MIT and Harvard have made the surprising discovery that the brain sees some faces as male when they appear in one area of a person's field of view, but female when they appear in a different location.
The findings challenge a longstanding tenet of neuroscience -- that how the brain sees an object should not depend on where the object is located relative to the observer, says Arash Afraz, a postdoctoral associate at MIT's McGovern Institute for Brain Research and lead author of a new paper on the work.
"It's the kind of thing you would not predict -- that you would look at two identical faces and think they look different," says Afraz. He and two colleagues from Harvard, Patrick Cavanagh and Maryam Vaziri Pashkam, described their findings in the Nov. 24 online edition of the journal Current Biology.
In the real world, the brain's inconsistency in assigning gender to faces isn't noticeable, because there are so many other clues: hair and clothing, for example. But when people view computer-generated faces, stripped of all other gender-identifying features, a pattern of biases, based on location of the face, emerges.
The researchers showed subjects a random series of faces, ranging along a spectrum of very male to very female, and asked them to classify the faces by gender. For the more androgynous faces, subjects rated the same faces as male or female, depending on where they appeared.
Study participants were told to fix their gaze at the center of the screen, as faces were flashed elsewhere on the screen for 50 milliseconds each. Assuming that the subjects sat about 22 inches from the monitor, the faces appeared to be about three-quarters of an inch tall.
The patterns of male and female biases were different for different people. That is, some people judged androgynous faces as female every time they appeared in the upper right corner, while others judged faces in that same location as male. Subjects also showed biases when judging the age of faces, but the pattern for age bias was independent from the pattern for gender bias in each individual.
Sample size
Afraz believes this inconsistency in identifying genders is due to a sampling bias, which can also be seen in statistical tools such as polls. For example, if you surveyed 1,000 Bostonians, asking if they were Democrats or Republicans, you would probably get a fairly accurate representation of these percentages in the city as a whole, because the sample size is so large. However, if you took a much smaller sample, perhaps five people who live across the street from you, you might get 100 percent Democrats, or 100 percent Republicans. "You wouldn't have any consistency, because your sample is too small," says Afraz.
He believes the same thing happens in the brain. In the visual cortex, where images are processed, cells are grouped by which part of the visual scene they analyze. Within each of those groups, there is probably a relatively small number of neurons devoted to interpreting gender of faces. The smaller the image, the fewer cells are activated, so cells that respond to female faces may dominate. In a different part of the visual cortex, cells that respond to male faces may dominate.
"It's all a matter of undersampling," says Afraz.
Michael Tarr, codirector of the Center for the Neural Basis of Cognition at Carnegie Mellon University, says the findings add to the growing evidence that the brain is not always consistent in how it perceives objects under different circumstances. He adds that the study leaves unanswered the question of why each person develops different bias patterns. "Is it just noise within the system, or is some other kind of learning occurring that they haven't figured out yet?" asks Tarr, who was not involved in the research. "That's really the fascinating question."

Tuning an 'Ear' to the Music of Gravitational Waves

A team of scientists and engineers at NASA's Jet Propulsion Laboratory has brought the world one step closer to "hearing" gravitational waves -- ripples in space and time predicted by Albert Einstein in the early 20th century.
The research, performed in a lab at JPL in Pasadena, Calif., tested a system of lasers that would fly aboard the proposed space mission called Laser Interferometer Space Antenna, or LISA. The mission's goal is to detect the subtle, whisper-like signals of gravitational waves, which have yet to be directly observed. This is no easy task, and many challenges lie ahead.
The new JPL tests hit one significant milestone, demonstrating for the first time that noise, or random fluctuations, in LISA's laser beams can be hushed enough to hear the sweet sounds of the elusive waves.
"In order to detect gravitational waves, we have to make extremely precise measurements," said Bill Klipstein, a physicist at JPL. "Our lasers are much noisier than what we want to measure, so we have to remove that noise carefully to get a clear signal; it's a little like listening for a feather to drop in the middle of a heavy rainstorm." Klipstein is a co-author of a paper about the lab tests that appeared in a recent issue of Physical Review Letters.
The JPL team is one of many groups working on LISA, a joint European Space Agency and NASA mission proposal, which, if selected, would launch in 2020 or later. In August of this year, LISA was given a high recommendation by the 2010 U.S. National Research Council decadal report on astronomy and astrophysics.
One of LISA's primary goals is to detect gravitational waves directly. Studies of these cosmic waves began in earnest decades ago when, in 1974, researchers discovered a pair of orbiting dead stars -- a type called pulsars -- that were spiraling closer and closer together due to an unexplainable loss of energy. That energy was later shown to be in the form of gravitational waves. This was the first indirect proof of the waves, and ultimately earned the 1993 Nobel Prize in Physics.
LISA is expected to not only "hear" the waves, but also learn more about their sources -- massive objects such as black holes and dead stars, which sing the waves like melodies out to the universe as the objects accelerate through space and time. The mission would be able to detect gravitational waves from massive objects in our Milky Way galaxy as well as distant galaxies, allowing scientists to tune into an entirely new language of our universe.
The proposed mission would amount to a giant triangle of three distinct spacecraft, each connected by laser beams. These spacecraft would fly in formation around the sun, about 20 degrees behind Earth. Each one would hold a cube made of platinum and gold that floats freely in space. As gravitational waves pass by the spacecraft, they would cause the distance between the cubes, or test masses, to change by almost imperceptible amounts -- but enough for LISA's extremely sensitive instruments to be able to detect corresponding changes in the connecting laser beams.
"The gravitational waves will cause the 'corks' to bob around, but just by a tiny bit," said Glenn de Vine, a research scientist and co-author of the recent study at JPL. "My friend once said it's sort of like rubber duckies bouncing around in a bathtub."
The JPL team has spent the last six years working on aspects of this LISA technology, including instruments called phase meters, which are sophisticated laser beam detectors. The latest research accomplishes one of their main goals -- to reduce the laser noise detected by the phase meters by one billion times, or enough to detect the signal of gravitational waves.
The job is like trying to find a proton in a haystack. Gravitational waves would change the distance between two spacecraft -- which are flying at 5 million kilometers (3.1 million miles) apart -- by about a picometer, which is about 100 million times smaller than the width of a human hair. In other words, the spacecraft are 5,000,000,000 meters apart, and LISA would detect changes in that distance on the order of .000000000005 meters!
At the heart of the LISA laser technology is a process known as interferometry, which ultimately reveals if the distances traveled by the laser beams of light, and thus the distance between the three spacecraft, have changed due to gravitational waves. The process is like combining ocean waves -- sometimes they pile up and grow bigger, and sometimes they cancel each other out or diminish in size.
"We can't use a tape measure to get the distances between these spacecraft," said de Vine, "So we use lasers. The wavelengths of the lasers are like our tick marks on a tape measure."
On LISA, the laser light is detected by the phase meters and then sent to the ground, where it is "interfered" via data processing (the process is called time-delay interferometry for this reason -- there's a delay before the interferometry technique is applied). If the interference pattern between the laser beams is the same, then that means the spacecraft haven't moved relative to each other. If the interference pattern changes, then they did. If all other reasons for spacecraft movement have been eliminated, then gravitational waves are the culprit.
That's the basic idea. In reality, there are a host of other factors that make this process more complex. For one thing, the spacecraft don't stay put. They naturally move around for reasons that have nothing to do with gravitational waves. Another challenge is the laser beam noise. How do you know if the spacecraft moved because of gravitational waves, or if noise in the laser is just making it seem as if the spacecraft moved?
This is the question the JPL team recently took to their laboratory, which mimics the LISA system. They introduced random, artificial noise into their lasers and then, through a complicated set of data processing actions, subtracted most of it back out. Their recent success demonstrated that they could see changes in the distances between mock spacecraft on the order of a picometer.
In essence, they hushed the roar of the laser beams, so that LISA, if selected for construction, will be able to hear the universe softly hum a tune of gravitational waves.
Other authors of the paper from JPL are Brent Ware; Kirk McKenzie; Robert E. Spero and Daniel A. Shaddock, who has a joint post with JPL and the Australian National University in Canberra.
LISA is a proposed joint NASA and European Space Agency mission. The NASA portion of the mission is managed by NASA's Goddard Space Flight Center, Greenbelt, Md. Some of the key instrumentation studies for the mission are being performed at JPL. The U.S. mission scientist is Tom Prince at the California Institute of Technology in Pasadena. JPL is managed by Caltech for NASA.

Saturday, November 27, 2010

How People Perceive Sour Flavors: Proton Current Drives Action Potentials in Taste Cells

This Thanksgiving, when the tartness of cranberry sauce smacks your tongue, consider the power of sour. Neurobiology researchers at the University of Southern California have made a surprising discovery about how some cells respond to sour tastes.
Of the five taste sensations -- sweet, bitter, sour, salty and umami -- sour is arguably the strongest yet the least understood. Sour is the sensation evoked by substances that are acidic, such as lemons and pickles. The more acidic the substance, the more sour the taste.
Acids release protons. How protons activate the taste system had not been understood. The USC team expected to find protons from acids binding to the outside of the cell and opening a pore in the membrane that would allow sodium to enter the cell. Sodium's entry would send an electrical response to the brain, announcing the sensation that we perceive as sour.
Instead, the researchers found that the protons were entering the cell and causing the electrical response directly.
The finding is to be published in the Proceedings of the National Academy of Sciences (PNAS).
"In order to understand how sour works, we need to understand how the cells that are responsive to sour detect the protons," said senior author Emily Liman, associate professor of neurobiology in the USC College of Letters, Arts and Sciences.
"In the past, it's been difficult to address this question because the taste buds on the tongue are heterogeneous. Among the 50 or so cells in each taste bud there are cells responding to each of the five tastes. But if we want to know how sour works, we need to measure activity specifically in the sour sensitive taste cells and determine what is special about them that allows them to respond to protons."
Liman and her team bred genetically modified mice and marked their sour cells with a yellow florescent protein. Then they recorded the electrical responses from just those cells to protons.
The ability to sense protons with a mechanism that does not rely on sodium has important implications for how different tastes interact, Liman speculates.
"This mechanism is very appropriate for the taste system because we can eat something that has a lot of protons and not much sodium or other ions, and the taste system will still be able to detect sour," she said. "It makes sense that nature would have built a taste cell like this, so as not to confuse salty with sour."
In the future, the research may have practical applications for cooks and the food industry.
"We're at the early stages of identifying the molecules that contribute to sour taste," Liman said. "Once we've understood the nature of the molecules that sense sour, we can start thinking about how they might be modified and how that might change the way things taste. We may also find that the number or function of these molecules changes during the course of development or during aging."

New Imaging Technique Accurately Finds Cancer Cells, Fast

The long, anxious wait for biopsy results could soon be over, thanks to a tissue-imaging technique developed at the University of Illinois.
The research team demonstrated the novel microscopy technique, called nonlinear interferometric vibrational imaging (NIVI), on rat breast-cancer cells and tissues. It produced easy-to-read, color-coded images of tissue, outlining clear tumor boundaries, with more than 99 percent confidence -- in less than five minutes.

Led by professor and physician Stephen A. Boppart, who holds appointments in electrical and computer engineering, bioengineering and medicine, the Illinois researchers will publish their findings on the cover of the Dec. 1 issue of the journalCancer Research.
In addition to taking a day or more for results, current diagnostic methods are subjective, based on visual interpretations of cell shape and structure. A small sample of suspect tissue is taken from a patient, and a stain is added to make certain features of the cells easier to see. A pathologist looks at the sample under a microscope to see if the cells look unusual, often consulting other pathologists to confirm a diagnosis.
"The diagnosis is made based on very subjective interpretation -- how the cells are laid out, the structure, the morphology," said Boppart, who is also affiliated with the university's Beckman Institute for Advanced Science and Technology. "This is what we call the gold standard for diagnosis. We want to make the process of medical diagnostics more quantitative and more rapid."
Rather than focus on cell and tissue structure, NIVI assesses and constructs images based on molecular composition. Normal cells have high concentrations of lipids, but cancerous cells produce more protein. By identifying cells with abnormally high protein concentrations, the researchers could accurately differentiate between tumors and healthy tissue -- without waiting for stain to set in.
Each type of molecule has a unique vibrational state of energy in its bonds. When the resonance of that vibration is enhanced, it can produce a signal that can be used to identify cells with high concentrations of that molecule. NIVI uses two beams of light to excite molecules in a tissue sample.
"The analogy is like pushing someone on a swing. If you push at the right time point, the person on the swing will go higher and higher. If you don't push at the right point in the swing, the person stops," Boppart said. "If we use the right optical frequencies to excite these vibrational states, we can enhance the resonance and the signal."
One of NIVI's two beams of light acts as a reference, so that combining that beam with the signal produced by the excited sample cancels out background noise and isolates the molecular signal. Statistical analysis of the resulting spectrum produces a color-coded image at each point in the tissue: blue for normal cells, red for cancer.
Another advantage of the NIVI technique is more exact mapping of tumor boundaries, a murky area for many pathologists. The margin of uncertainty in visual diagnosis can be a wide area of tissue as pathologists struggle to discern where a tumor ends and normal tissue begins. The red-blue color coding shows an uncertain boundary zone of about 100 microns -- merely a cell or two.
"Sometimes it's very hard to tell visually whether a cell is normal or abnormal," Boppart said. "But molecularly, there are fairly clear signatures."
The researchers are working to improve and broaden the application of their technique. By tuning the frequency of the laser beams, they could test for other types of molecules. They are working to make it faster, for real-time imaging, and exploring new laser sources to make NIVI more compact or even portable. They also are developing new light delivery systems, such as catheters, probes or needles that can test tissue without removing samples.
"As we get better spectral resolution and broader spectral range, we can have more flexibility in identifying different molecules," Boppart said. "Once you get to that point, we think it will have many different applications for cancer diagnostics, for optical biopsies and other types of diagnostics."
The National Cancer Institute of the National Institutes of Health sponsored the study. Other co-authors were Beckman Institute researchers Praveen Chowdary, Zhi Jiang, Eric Chaney, Wladimir Benalcazar and Daniel Marks, and professor of chemistry and physics Martin Gruebele.

Polar Bears Unlikely to Survive in Warmer World, According to Biologists

Will polar bears survive in a warmer world? UCLA life scientists present new evidence that their numbers are likely to dwindle.
As polar bears lose habitat due to global warming, these biologists say, they will be forced southward in search of alternative sources of food, where they will increasingly come into competition with grizzly bears.

To test how this competition might unfold, the UCLA biologists constructed three-dimensional computer models of the skulls of polar bears and grizzly bears -- a subspecies of brown bears -- and simulated the process of biting. The models enabled them to compare the two species in terms of how hard they can bite and how strong their skulls are.
"What we found was striking," said Graham Slater, a National Science Foundation-funded UCLA postdoctoral scholar in ecology and evolutionary biology and lead author of the research. "The polar bear and brown bear can bite equally hard, but the polar bear's skull is a much weaker structure."
The implication is that polar bears are likely to lose out in competition for food to grizzlies as warmer temperatures bring them into the same environments, because grizzlies' stronger skulls are better suited to a plant-rich diet, said Slater and Blaire Van Valkenburgh, UCLA professor of ecology and evolutionary biology and senior author of the research.
"The result for polar bears may be lower weight, smaller and fewer litters, less reproductive success, fewer that would survive to adulthood, and dwindling populations," Van Valkenburgh said. "Then you can get into an extinction vortex, where a small population becomes even smaller in a downward spiral to extinction.
"To people who say polar bears can just change their diet, we are saying they will change their diet -- they will have to -- but it probably will not be sufficient for them, especially if they are co-existing with grizzly bears. Their skull is relatively weak and not suited to adapting its diet. We did not expect to find what we found."
"This is one additional piece of evidence that things look pretty bleak for the polar bear if current trends continue," Slater said.
The research, federally funded by the National Science Foundation, was published this month in the online journalPLoS ONE, a publication of the Public Library of Science.
Polar bears are a "marvelous example of rapid adaptation to an extreme environment," Slater said. "The fact that we can lose them equally as rapidly as a result of human-mediated climate change is rather striking. Polar bears are very well suited to do what they do, but they are highly specialized and not well suited to doing much else."
It could take quite some time for polar bears to go extinct, Van Valkenburgh said, but they are likely to become much more rare than today.
Polar bears are losing habitat as a result of global warming and the associated loss of arctic sea ice, which they use to hunt for seals, Van Valkenburgh and Slater said. But could they survive on an alternative food source?
"Our results suggest that this is not too likely," Slater said. "The polar bear's skull is a relatively weak structure that is not suited to diets consisting of a lot of plant material like that of the brown bear. As climate change continues, polar bears will be forced to move south in search of resources, while brown bears move north as their climate becomes more mild. When these two species meet, as they have already begun to, it seems that brown bears will easily out-compete polar bears. Our findings should serve as a warning that polar bears may not be flexible enough to survive if current trends continue.
"Chewing a lot of vegetables takes quite a lot of force to grind up," Slater said. "Grizzly bears are well suited to eating these kinds of food, but the polar bear is not well suited for it. The grizzly has a much more efficient skull for eating these kinds of foods."
In Canada, grizzly bears are moving north and are already in polar bear territory, Van Valkenburgh and Slater said.
The life scientists -- whose co-authors include UCLA undergraduates Leeann Louis and Paul Yang and graduate student Borja Figueirido from Spain's Universidad de Malaga, Campus Universitario de Teatinos -- studied two adult male skulls from museums, one of a polar bear from Canada, the other of a grizzly from Alaska. They built 3-D computer models of the skulls and then analyzed their biomechanics.
"We can apply muscle forces to the skull to simulate biting, and we can measure how hard the animal could bite. We can measure stress and strain in the skull as well," Slater said. "We found that while the stresses in the grizzly bear skull are relatively low, the same bites in the polar bear produce much more stress. Combined with other evidence from Blaire's laboratory, this tells us that the smaller teeth of polar bears are less suited to diets that consist of plants, grass, vegetation and berries."
"Polar bears would not be able to break up the food as well in their mouths and would not digest it as well," Van Valkenburgh said.
In the timeline of evolution, polar bears evolved from the brown bear very recently, and the two are very closely related, Van Valkenburgh and Slater said. Genetic studies indicate that the split between polar bears and brown bears occurred only 500,000 to 800,000 years ago -- the most recent split between any of the eight bear species.
Despite the recentness of the split between these two species, their skulls and teeth are extremely different, probably as a result of where they live (arctic versus temperate regions) and the differences in their diets. Grizzly bears have very large molar teeth, while polar bears have teeth that are much smaller. Polar bears eat seal blubber, which is soft and does not require much chewing, while brown bears consume many plants.
The biologists investigated the rate at which skull shape has evolved in the bear family. They found that the rate of evolution in the branch of the bear family tree leading to the polar bear was twice as fast as the rates in other branches of the tree; it appears that skull shape evolved extremely rapidly in polar bears.
Polar bears probably evolved very rapidly in response to glacial climates during the ice ages, Slater said.
"You don't see many bears that look like polar bears, and the difference in skull shape evolved very rapidly," Slater said.



Monday, November 8, 2010

TB-Drugome Provides New Targets for Anti-Tuberculosis Drug Discovery

Researchers at the University of California, San Diego School of Medicine and the University of Leeds have linked hundreds of federally approved drugs to more than 1,000 proteins in Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), opening new avenues to repurpose these drugs to treat TB.

The study was published Nov. 4 inPLoS Computational Biology.
"Tuberculosis is currently one of the most widely spread infectious diseases, with an estimated one-third of the world's population infected and between one and two million people dying each year from the disease," said Philip Bourne, PhD, professor of pharmacology at UCSD's Skaggs School of Pharmacy and Pharmaceutical Sciences. "The continuing emergence of M. tuberculosis strains resistant to all existing, affordable drug treatments requires the development of novel, effective and inexpensive drugs.
The newly developed TB-drugome may help that effort, Bourne said, by identifying new M. tuberculosis protein targets that can be perturbed by a variety of existing drugs prescribed for other purposes.
Sarah Kinnings at the University of Leeds and a team of scientists at UC San Diego, led by Bourne (who is also associate director of the RCSB Protein Data Bank) and research scientist Lei Xie, PhD, used a novel computational strategy to investigate whether any existing drugs were able to bind to any of the approximately 40 percent of proteins in the M. tuberculosis proteome with decipherable three-dimensional structures.
The researchers not only discovered that approximately one-third of the drugs examined may have the potential to be repurposed to treat tuberculosis, but also that many currently unexploited M. tuberculosis proteins could serve as novel anti-tubercular targets. This finding led the investigators to construct a complex network of drug-target interactions -- a TB-drugome available to all scientists.
While this new computational, high-throughput process of drug discovery is promising, Xie cautioned that "only experimentation can validate the most promising drug-target combinations, and there will be many failures along the way."
Kinnings added that any drugs subsequently confirmed to bind to M. tuberculosis proteins may need to be modified to increase their ability to penetrate the bacterial cell membrane, reduce their required dosage, and improve other pharmacological properties. The screening of a large collection of analogs to known drugs will be the next step towards anti-tuberculosis drug discovery.
Other authors of the study are Richard Jackson of the Institute of Molecular and Cellular Biology and Astbury Centre for Structural Molecular Biology at University of Leeds; Li Xie of the Skaggs School of Pharmacy and Pharmaceutical Sciences at UC San Diego and Kingston Fung of the UCSD's Bioinformatics Program.
Funding for this project came from the National Institutes of Health.

Tarantulas help scientists break down human fear

Scientists using tarantulas to unpick human fear have found that the brain responds differently to threats based on proximity, direction and how scary people expect something to be.
Researchers from the Cognition and Brain Sciences Unit in Cambridge, England used functional magnetic resonance imaging, or fMRI, to track brain activity in 20 volunteers as they watched a tarantula placed near their feet, and then moved closer.

Their results suggest that different components of the brain's fear network serve specific threat-response functions and could help scientists diagnose and treat patients who suffer from clinical phobias.
"We've shown that it's not just a single structure in the brain, it's a number of different parts of the fear network and they are working together to orchestrate the fear response," Dean Mobbs, who led the study, said in a telephone interview.
Mobbs's team assessed the volunteers' brain activity during three sections of the study: first when the tarantula was in a segmented box near their foot and then moved either to nearer or more distant compartments of the box, and also when the spider walked in different directions.
"It seems that when a spider is further away moves closer to you, you see a switch from the anxiety regions of the brain to the panic regions," said Mobbs.
He said there was more activity in the brain's panic response center when the tarantula crept closer than when it retreated, regardless of how close it was in the first place.
He explained that the volunteers were actually watching an elaborately rigged video of a tarantula which they believed was near their foot, since getting the spider to do the same thing for each volunteer would have been impossible.
The scientists also asked volunteers beforehand how scared they thought they might be of the tarantula, and found that those who thought they would be most scared had a false impression afterwards of how large the spider was.
The scientists think it may be this so-called "expectation error" that could be the key to people developing a phobia -- an irrational, intense and persistent fear of certain things, people, animals or situations.
"This may be one cognitive mechanism by which people acquire phobias," said Mobbs. He said that since the expectation of great fear appeared to make a person exaggerate the size of the threat in their mind, this could trigger a "cascade effect," distorting the other processes in the brain to react to a larger threat and panic yet more as it came closer.

Beetle Study Suggests, Genetic 'Battle of the Sexes' More Important to Evolution Than Thought

A new study of beetles shows a genetic 'battle of the sexes' could be much harder to resolve and even more important to evolution than previously thought.
This battle, observed across many species and known as intralocus sexual conflict, happens when the genes for a trait which is good for the breeding success of one sex are bad for the other -- sparking an 'evolutionary tug-o-war' between the sexes.
It has previously been thought these issues were only resolved when the trait in question evolves to become sex-specific in its development -- meaning the trait only develops in the gender it benefits and stops affecting the other. An example of this is male peacocks' tails, used for mating displays, which are not present in females.
However, a new study by the universities of Exeter (UK), Okayama and Kyushu (both Japan) published Nov. 4 in Current Biology shows this doesn't always bring an end to conflict -- as even when the trait becomes sex-specific, knock-on effects can still disadvantage the other sex.
Professor Dave Hosken, from the Centre for Ecology & Conservation (Cornwall) at the University of Exeter, said: "This kind of genetic tussle is everywhere in biology. For example, in humans, male hips are optimised for physical activity, whereas female hips also need to allow child bearing. That's the sort of evolutionary conflict we're talking about, and these conflicts were previously thought to be resolved by sex-specific trait development.
"What we're seeing in this study is that this isn't always the end of the sexual conflict. This means it's no longer clear how or when, if ever, these conflicts get fully resolved and this means it could be more important to the evolutionary process than has generally been thought."
In this study, the researchers looked at broad-horned flour beetles, where males have massively enlarged mandibles used to fight other males for mating supremacy. The enlarged mandibles aren't present in the females at all -- meaning this is a sex-specific trait.
By selectively breeding the beetles for larger or smaller mandible size, the researchers were able to show that the bigger the mandibles were -- the more successful the males were in breeding. There was a corresponding counter-effect on females, however, as females from larger mandibled populations were less successful.
Professor Takahisa Miyatake, from the Graduate School of Environmental Science at Okayama University, said: "We looked at all the possible reasons for this and found that while the females did not develop the larger mandibles, they did inherit many of the other characteristics that made the enlarged mandibles possible in males. This included a reduced abdomen size, which could affect the number of eggs a female can carry -- giving a possible explanation for the disadvantage.
"So here we see a sex-specific trait which is still having a negative effect on the sex which doesn't show it. This means that even though it looks like this genetic conflict is over, it's still ongoing and there's no easy way to end it."
Kensuke Okada, also from Okayama University, said: "The view that sex-limited trait development resolves this kind of genetic battle of the sexes is based on the assumption that traits are genetically independent of each other, which is frequently not true.
"What we're seeing here is that genetic architecture can provide a general barrier to this kind of conflict resolution."

Friday, November 5, 2010

New Statistical Model Moves Human Evolution Back Three Million Years

Evolutionary divergence of humans from chimpanzees likely occurred some 8 million years ago rather than the 5 million year estimate widely accepted by scientists, a new statistical model suggests.
The revised estimate of when the human species parted ways from its closest primate relatives should enable scientists to better interpret the history of human evolution, said Robert D. Martin, curator of biological anthropology at the Field Museum, and a co-author of the new study appearing in the journal Systematic Biology. 

Working with mathematicians, anthropologists and molecular biologists, Martin has long sought to integrate evolutionary information derived from genetic material in various species with the fossil record to get a more complete picture.
Comparing DNA among related animals can provide a clear picture of how their shared genes evolved over time, giving rise to new and separate species, Martin said. But such molecular information doesn't yield a timetable showing when the genetic divergence occurred.
Fossil evidence is the only direct source of information about long-extinct species and their evolution, Martin and his colleagues said, but large gaps in the fossil record can make such information difficult to interpret. For a generation, paleontologists have estimated human origins at 5 million to 6 million years ago.
But that estimate rests on a thin fossil record. By looking at all of today's primate species, all of the known fossil primates and using DNA evidence, computer models suggest a longer evolutionary timetable. The new analysis described in the Systematic Biology paper takes into account gaps in the fossil record and fills in those gaps statistically.
Such modeling techniques, which are widely used in science and commerce, take into account more overall information than earlier processes used to estimate evolutionary history using just a few individual fossil dates, Martin said. It can give scientists a broader perspective for interpreting data.
One example is a skull fossil discovered in Chad (central Africa) earlier in this decade. The fossil, named Sahelanthropus tchadensis and nicknamed Toumaï (which means "hope of life" in the local Goran language), raised great interest because it has many human characteristics. But consensus on how to classify the discovery has been elusive particularly because the fossil is about 7 million years old, well beyond the accepted time frame for human evolution.
Under the new estimate, Toumaï would fall within the period after the human lineage split from chimpanzees, Martin said.
The new approach to dating evolutionary history builds on earlier work by Martin and colleagues. In 2002, they published a paper in Nature that argues the last common ancestor of today's primates lived some 85 million years ago.
This implies that for 20 million years before dinosaurs became extinct, early versions of primates also lived and evolved. It challenged the accepted theory that primates and other mammals didn't really thrive on the planet until dinosaurs were gone.

Thursday, November 4, 2010

Fourth Flavor of Neutrino? Physics Experiment Suggests Existence of New Elementary Particle

The results of a high-profile Fermilab physics experiment appear to confirm strange 20-year-old findings that poke holes in the standard model, suggesting the existence of a new elementary particle: a fourth flavor of neutrino.

The new results go further to describe a violation of a fundamental symmetry of the universe asserting that particles of antimatter behave in the same way as their matter counterparts.
Neutrinos are neutral elementary particles born in the radioactive decay of other particles. The known "flavors" of neutrinos are the neutral counterparts of electrons and their heavier cousins, muons and taus. Regardless of a neutrino's original flavor, the particles constantly flip from one type to another in a phenomenon called "neutrino flavor oscillation."
An electron neutrino might become a muon neutrino, and then later an electron neutrino again. Scientists previously believed three flavors of neutrino exist. In this Mini Booster Neutrino Experiment, dubbed MiniBooNE, researchers detected more oscillations than would be possible if there were only three flavors.
"These results imply that there are either new particles or forces we had not previously imagined," said Byron Roe, professor emeritus in the University of Michigan's Department of Physics, and an author of a paper on the results newly published online in Physical Review Letters.
"The simplest explanation involves adding new neutrino-like particles, or sterile neutrinos, which do not have the normal weak interactions."
The three known types of neutrino interact with matter primarily through the weak nuclear force, which makes them difficult to detect. It is hypothesized that this fourth flavor would not interact through the weak force, making it even harder to find.
The existence of sterile neutrinos could help explain the composition of the universe, said William Louis, a scientist at Los Alamos National Laboratory who was a doctoral student of Roe's at U-M and is involved in the MiniBooNE experiment.
"Physicists and astronomers are looking for sterile neutrinos because they could explain some or even all of the dark matter of the universe," Louis said. "Sterile neutrinos could also possibly help explain the matter asymmetry of the universe, or why the universe is primarily composed of matter, rather than antimatter."
The MiniBooNE experiment, a collaboration among some 60 researchers at several institutions, was conducted at Fermilab to check the results of the Liquid Scintillator Neutrino Detector (LSND) experiment at Los Alamos National Laboratory, which started in 1990. The LSND was the first to detect more neutrino oscillations than the standard model predicted.
MiniBooNE's initial results several years ago, based on data from a neutrino beam (as opposed to an antineutrino beam), did not support the LSND results. The LSND experiment was conducted using an antineutrino beam, though, so that was the next step for MiniBooNE.
These new results are based on the first three years of data from an antineutrino beam, and they tell a different story than the earlier results. MiniBooNE's antineutrino beam data does support the LSND findings. And the fact that the MiniBooNE experiments produced different results for antineutrinos than for neutrinos especially astounds physicists.
"The fact that we see this effect in antineutrinos and not in neutrinos makes it even more strange," Roe said. "This result means even more serious additions to our standard model would be necessary than had been thought from the first LSND result."
The result seems to violate the "charge-parity symmetry" of the universe, which asserts that the laws of physics apply in the same ways to particles and their counterpart antiparticles. Violations of this symmetry have been seen in some rare decays, but not with neutrinos, Roe said.
While these results are statistically significant and do support the LSND findings, the researchers caution that they need results over longer periods of time, or additional experiments before physicists can rule out the predictions of the standard model.

New Retinal Implant Enables Blind People to See Shapes and Objects

Research published in Proceedings of the Royal Society B reveals that a group of researchers based in Germany have developed a retinal implant that has allowed three blind people to see shapes and objects within days of the implant being installed.

One blind person was even able to identify and find objects placed on a table in front of him, as well as walking around a room independently and approaching people, reading a clock face and differentiating seven shades of grey. The device, which has been developed by the company Retinal Implant AG together with the Institute for Ophthalmic Research at the University of Tuebingen, represents an unprecedented advance in electronic visual prostheses and could eventually revolutionise the lives of up 200,000 people worldwide who suffer from blindness as a result of retinitis pigmentosa, a degenerative eye disease.
In this disease light receptors in the eye cease to function. Writing in Proceedings of the Royal Society B, Prof. Dr. Eberhart Zrenner (founding Director of Retinal Implant AG and Director and Chairman of the University of Tuebingen Eye Hospital) states that "The results of this pilot study provide strong evidence that the visual functions of patients blinded by a hereditary retinal dystrophy can, in principle, be restored to a degree sufficient for use in daily life."
The device -- known as a subretinal implant -- sits underneath the retina, directly replacing light receptors lost in retinal degeneration. As such, it uses the eyes' natural image processing capabilities beyond the light detection stage to produce a visual perception in the patient that is stable and follows their eye movements. Other types of retinal implants -- known as epiretinal implants -- sit outside the retina and because they bypass the intact light-sensitive structures in the eyes they require the user to wear an external camera and processor unit.
The subretinal implant described in this paper achieves unprecedented clarity because it has a great deal more light receptors than other similar devices. As Prof. Dr. Zrenner states, "The present study...presents proof-of-concept that such devices can restore useful vision in blind human subjects, even though the ultimate goal of broad clinical application will take time to develop."

Wednesday, November 3, 2010

Children born by Caesarean are calmer, claims study

Children born after a Caesarean requested by the mother are calmer with fewer emotional and behavioural problems, claim researchers. 
During pre-school years they are much less likely to suffer problems such as anxiety, aggression and attention disorders, according to a Chinese study.
Those born with the help of forceps or a suction cup were 40 per cent more likely to be among the worst affected by such problems.
Previous research suggested babies born using 'assisted delivery' techniques have the highest levels of stress hormones on arrival, and this may affect early development.
The study involving 4,190 pre-school children from southeast China looked at the different modes of delivery and links with childhood behaviour. 
China has the highest rate of Caesarean section in the world with around half of babies delivered surgically, according to the World Health Organisation. 
About one in four babies in the UK are delivered by Caesarean, most of them in emergencies or at the request of doctors for medical reasons.
About seven per cent of all NHS surgical births - around 10,000 babies a year - follow a request from the mother for no medical reason.
British research last month found regional differences were not down to mothers being 'too posh to push' but variations in decisions made by doctors facing a similar set of complications.
In the latest study, two per cent of births were elective Caesarean and 85 per cent were spontaneous delivery. Just over 500 - 12 per cent - were assisted births. 
Parents were asked to complete a standard list measuring emotional and behavioural problems in the early years, says a study in BJOG: An International Journal of Obstetrics and Gynaecology. 
The link between mode of delivery and subsequent childhood emotional and behavioural problems is possibly related to high levels of the stress hormone cortisol. 
Immediately after birth, cord blood cortisol levels have been found to be lowest in babies born by elective Caesarean followed by spontaneous vaginal birth. 
The highest levels are found in assisted deliveries where forceps or a suction cup is used because labour is prolonged and complications may have developed.
Previous studies have suggested these children experienced the highest levels of stress during birth.  
Professor Jianmeng Liu, Deputy Director of the Institute of Reproductive and Child Health, Peking University Health Science Centre, Beijing, one of the authors on the paper said it was the first time research has looked at the effect of caesarean delivery on maternal request on childhood behaviour, known as psychopathology. 
He said 'Cortisol levels have been linked to childhood psychopathology, however, more studies are still needed to look at this in more detail.'
Professor Philip Steer, BJOG editor-in-chief said 'With the rising rates of elective caesarean section in China and in other countries, it is interesting to see from this research that there is a low impact on childhood psychopathology. 
'Assisted vaginal delivery can be more traumatic for both the mother and child hence the rise in cortisol levels. 
'More research is needed however to look at the specific link between assisted delivery such as forceps and psychopathology in children.'

Autism brain secrets revealed by scan


Differences in the brain structure of people carrying an "autism gene" may offer clues to how the condition develops, say US scientists.
Scans revealed children carrying the gene variant appeared to have more nerve cell "connections" within the frontal lobe.
They had fewer connections between this and the rest of the brain, reported Science Translational Medicine journal.
Brain research has just begun to reveal autism's roots, a UK expert said.
One-third of the population carry the CNTNAP2 gene variant, so it does not guarantee that autism will develop, but just slightly increases the risk.
Different pathways
However, scientists at the University of California in Los Angeles believe it may influence the way the brain is "wired".
They used functional magnetic resonance imaging (fMRI) to look for communication between different brain regions, and to measure the strength of these connections.
They scanned the brains of 32 children as they performed learning-related tasks - half had autism, and half did not.
Regardless of their diagnosis, those carrying the CNTNAP2 variant had differences in the connections within the frontal lobe of the brain itself and between the frontal lobe and the rest of the brain.
Dr Ashley Scott-Van Zeeland, who led the research, said: "The front of the brain appears to talk mostly to itself - it doesn't communicate as much with other parts of the brain and lacks long-range connections to the back of the brain."

The researchers also spotted differences in the "wiring" between the frontal lobe and the left and right sides of the brain.
In children with the version of the gene not linked to autism risk, the pathways were linked more strongly to the left side of the brain.
In those with the "risk variant", the pathways were different, linking the lobe strongly to both sides of the brain.
This, said the researchers, could explain why the gene variant had been linked to children who are slow in starting to talk.
Dr Scott-Van Zeeland said that if the gene variant did predict language problems, then it might be possible to design therapies which helped to "rebalance" the brain and encourage normal development.
Professor Margaret Esiri, a neuroscientist from Oxford University, said that researchers had so far "barely scratched the surface" of understanding the interplay between genes and brain development.
Her own research closely analyses a scarce supply of donated brains from both autistic and non-autistic adults and children to look for differences in structure and function.
She said: "If you understand these subtle differences, there may be ways of 'tweaking' them earlier in life, and bringing them back into a normal trajectory of development. Of course, this would be many years away."
Carol Povey, from the National Autistic Society, said the study was interesting because it began to link genes thought to be involved in autism to actual changes in brain function.
She said: "The causes of autism are as yet unknown, but we do know there are likely to be many factors involved, so we hope this will contribute to our understanding of this complex condition."