郑少群博客: 五月 2015

2015年5月14日星期四

Baboons prefer to spend time with others of the same age, status and even personality -- ScienceDaily

A team of researchers led by the University of Cambridge and international conservation charity the Zoological Society of London says that this may act as a barrier to the transfer of new social information to the wider troop, as previous research done by the team shows baboons of a certain age and personality type -- the younger, bolder animals -- are more likely to be information 'generators': those who solve new foraging problems.

Given that information generators spend much of their time in the company of similar baboons, researchers say there is a risk that acquired information may end up exclusively confined to other information generators, thus decreasing the likelihood of new knowledge being disseminated to the wider troop.

Research teams tracked the same two baboon troops from dawn until dusk across Namibia's Tsaobis Nature Park over several months each year between 2009-2014 to observe patterns of behaviour. The study is the first to monitor baboon social network structures over such a timescale and is published today in the journal Royal Society Open Science.

"Within these big troop networks over time social preferences are generally dictated by age, rank, personality and so on," said Dr Alecia Carter, from the University of Cambridge's Department of Zoology, first author of the study. "This happens in humans all the time; we hang out with people who have the same income, religion, education etc. Essentially, it's the same in baboons."

To test for the personality traits of 'boldness' -- essentially an assertive curiosity -- the researchers planted unfamiliar foods on the edge of paths commonly used by baboon troops. These stimuli included hard-boiled eggs and small bread rolls dyed red or green. The research team then measured the time spent on investigating the new foodstuff, and whether they ate it, to determine a scale of boldness for members of the baboon troops.

"Our analysis is the first to suggest that bolder and shyer baboons are more likely to associate with others that share this personality trait," said Dr Guy Cowlishaw from the Zoological Society of London, senior author of the study. "Previous studies in other animals -- from chimps to guppies -- suggests that time spent in the company of those with similar personalities could promote cooperation among individuals.

"Why baboons should demonstrate homophily for boldness is unclear, but it could be a heritable trait, and the patterns we're seeing reflect family associations."

Perhaps surprisingly, says Carter, gender was not a particular obstacle to social interaction, with females preferring to groom males. This is, in part, due to the obvious sexual engagements for breeding, but also as a tactic on the part of females to curry favour with particular males for the sake of their offspring.

"Chacma baboon males will often commit infanticide, killing the babies of rivals. Female baboons try and get around this by being as promiscuous as possible to confuse the paternal identity -- so males find it harder to tell if they are killing a rival's offspring or their own," added Dr Carter.

"They will also try and form bonds with particular males in the hope that they will protect their offspring and let the babies forage in good places with them -- although males tend to be fairly lazy when it comes to this; it's up to the babies to follow the males to good food."

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New class of 'dark' globular star clusters discovered around giant galaxy Centaurus A -- ScienceDaily

Globular star clusters are huge balls of thousands of stars that orbit most galaxies. They are among the oldest known stellar systems in the Universe and have survived through almost the entire span of galaxy growth and evolution.

Matt Taylor, a PhD student at the Pontificia Universidad Catolica de Chile, Santiago, Chile, and holder of an ESO Studentship, is lead author of the new study. He sets the scene: "Globular clusters and their constituent stars are keys to understanding the formation and evolution of galaxies. For decades, astronomers thought that the stars that made up a given globular cluster all shared the same ages and chemical compositions -- but we now know that they are stranger and more complicated creatures."

The elliptical galaxy Centaurus A (also known as NGC 5128) is the closest giant galaxy to the Milky Way and is suspected to harbour as many as 2000 globular clusters. Many of these globulars are brighter and more massive than the 150 or so orbiting the Milky Way.

Matt Taylor and his team have now made the most detailed studies so far of a sample of 125 globular star clusters around Centaurus A using the FLAMES instrument on ESO's Very Large Telescope at the Paranal Observatory in northern Chile [1].

They used these observations to deduce the mass of the clusters [2] and compare this result with how brightly each of the clusters shines.

For most of the clusters in the new survey, the brighter ones had more mass in the way that was expected -- if a cluster contains more stars it has greater total brightness and more total mass. But for some of the globulars something strange showed up: they were many times more massive than they looked. And even more strangely, the more massive these unusual clusters were, the greater the fraction of their material was dark. Something in these clusters was dark, hidden and massive. But what?

There were several possibilities. Perhaps the dark clusters contain black holes, or other dark stellar remnants in their cores? This may be a factor that explains some of the hidden mass, but the team concludes that it cannot be the whole story. What about dark matter? Globular clusters are normally considered to be almost devoid of this mysterious substance, but perhaps, for some unknown reason, some clusters have retained significant dark matter clumps in their cores. This would explain the observations but does not fit into conventional theory.

Co-author Thomas Puzia adds: "Our discovery of star clusters with unexpectedly high masses for the amount of stars they contain hints that there might be multiple families of globular clusters, with differing formation histories. Apparently some star clusters look like, walk like, and smell like run-of-the-mill globulars, but there may quite literally be more to them than meets the eye."

These objects remain a mystery. The team is also engaged in a wider survey of other globular clusters in other galaxies and there are some intriguing hints that such dark clusters may also be found elsewhere.

Matt Taylor sums up the situation: "We have stumbled on a new and mysterious class of star cluster! This shows that we still have much to learn about all aspects of globular cluster formation. It's an important result and we now need to find further examples of dark clusters around other galaxies."

Notes

[1] Up to now astronomers have studied star clusters to this detail only in the Local Group. The relatively small distances make direct measurements of their masses possible. Looking at NGC 5128, which is an isolated, massive elliptical galaxy just outside the Local Group about 12 million light-years away, they were able to estimate masses of globular clusters in a completely different environment by pushing VLT/FLAMES to its limits.

[2] The FLAMES observations provide information about the motions of the stars in the clusters. This orbital information depends on the strength of the gravitational field and can hence be used to deduce the mass of the cluster -- astronomers call such estimates dynamical masses. The light gathering power of a 8.2-metre VLT Unit Telescope mirror and FLAMES's ability to observe more than 100 clusters simultaneously was the key to collecting the data necessary for the study.

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Brains of smokers who quit successfully might be wired for success -- ScienceDaily

The study, published in Neuropsychopharmacology, showed greater connectivity among certain brain regions in people who successfully quit smoking compared to those who tried and failed.

The researchers analyzed MRI scans of 85 people taken one month before they attempted to quit. All participants stopped smoking and the researchers tracked their progress for 10 weeks. Forty-one participants relapsed. Looking back at the brain scans of the 44 smokers who quit successfully, the researchers found they had something in common before they stopped smoking -- better synchrony (coordinated activity) between the insula, home to urges and cravings, and the somatosensory cortex, a part of the brain that is central to our sense of touch and motor control.

"Simply put, the insula is sending messages to other parts of the brain that then make the decision to pick up a cigarette or not," said Merideth Addicott, Ph.D., assistant professor at Duke and lead author of the study.

The insula, a large region in the cerebral cortex, has been the subject of many smoking cessation studies that show this area of the brain is active when smokers are craving cigarettes, said Joseph McClernon, Ph.D., associate professor at Duke and the study's senior author. Other studies have found that smokers who suffer damage to the insula appear to spontaneously lose interest in smoking.

"There's a general agreement in the field that the insula is a key structure with respect to smoking and that we need to develop cessation interventions that specifically modulate insula function," McClernon said. "But in what ways do we modulate it, and in whom? Our data provides some evidence on both of those fronts, and suggests that targeting connectivity between insula and somatosensory cortex could be a good strategy."

Neurofeedback and transcranial magnetic stimulation, used to improve depression, are two treatments that modulate brain activity. With the findings in this study, researchers now have more information on where to further investigate, McClernon said.

"We have provided a blueprint," McClernon said. "If we can increase connectivity in smokers to look more like those who quit successfully, that would be a place to start. We also need more research to understand what it is exactly about greater connectivity between these regions that increases the odds of success."

In addition to Addicott and McClernon, study authors include Maggie Sweitzer; Brett Froeliger; and Jed Rose. The researchers received funding from the National Institute on Drug Abuse (R01 DA025876; K01 DA033347). McClernon is also a site principal investigator on an investigator-initiated grant (GRAND) from Pfizer, Inc.

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U.S. beekeepers lost 40 percent of bees in 2014-15 -- ScienceDaily

The survey, which asks both commercial and small-scale beekeepers to track the health and survival rates of their honey bee colonies, is conducted each year by the Bee Informed Partnership in collaboration with the Apiary Inspectors of America, with funding from the U.S. Department of Agriculture (USDA). A summary of the 2014-2015 results is available upon request prior to May 13, 2015; thereafter the results will be added to previous years' results publicly available on the Bee Informed website.

"We traditionally thought of winter losses as a more important indicator of health, because surviving the cold winter months is a crucial test for any bee colony," said Dennis vanEngelsdorp, an assistant professor of entomology at the University of Maryland and project director for the Bee Informed Partnership. "But we now know that summer loss rates are significant too. This is especially so for commercial beekeepers, who are now losing more colonies in the summertime compared to the winter. Years ago, this was unheard of."

Beekeepers who responded to the survey lost a total of 42.1 percent of their colonies over the course of the year. Winter loss rates decreased from 23.7 percent last year to 23.1 percent this year, while summer loss rates increased from 19.8 percent to 27.4 percent.

Among backyard beekeepers (defined as those who manage fewer than 50 colonies), a clear culprit in losses is the varroa mite, a lethal parasite that can easily spread between colonies. Among commercial beekeepers, the causes of the majority of losses are not as clear.

"Backyard beekeepers were more prone to heavy mite infestations, but we believe that is because a majority of them are not taking appropriate steps to control mites," vanEngelsdorp said. "Commercial keepers were particularly prone to summer losses. But they typically take more aggressive action against varroa mites, so there must be other factors at play."

This is the ninth year of the winter loss survey, and the fifth year to include summer and annual losses in addition to winter loss data. More than 6,000 beekeepers from all 50 states responded to this year's survey. All told, these beekeepers are responsible for nearly 15 percent of the nation's estimated 2.74 million managed honey bee colonies.

The survey is part of a larger research effort to understand why honey bee colonies are in such poor health, and what can be done to manage the situation. Colony losses present a financial burden for beekeepers, and can lead to shortages among the many crops that depend on honey bees as pollinators. Some crops, such as almonds, depend entirely on honey bees for pollination. Estimates of the total economic value of honey bee pollination services range between $10 billion and $15 billion annually.

"The winter loss numbers are more hopeful especially combined with the fact that we have not seen much sign of Colony Collapse Disorder (CCD) for several years, but such high colony losses in the summer and year-round remain very troubling," said Jeffery Pettis, a senior entomologist at U.S. Department of Agriculture and a co-coordinator of the survey. "If beekeepers are going to meet the growing demand for pollination services, researchers need to find better answers to the host of stresses that lead to both winter and summer colony losses."

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Drug perks up old muscles and aging brains -- ScienceDaily

Researchers at the University of California, Berkeley, have discovered that a small-molecule drug simultaneously perks up old stem cells in the brains and muscles of mice, a finding that could lead to drug interventions for humans that would make aging tissues throughout the body act young again.

"We established that you can use a single small molecule to rescue essential function in not only aged brain tissue but aged muscle," said co-author David Schaffer, director of the Berkeley Stem Cell Center and a professor of chemical and biomolecular engineering. "That is good news, because if every tissue had a different molecular mechanism for aging, we wouldn't be able to have a single intervention that rescues the function of multiple tissues."

The drug interferes with the activity of a growth factor, transforming growth factor beta 1 (TGF-beta1), that Schaffer's UC Berkeley colleague Irina Conboy showed over the past 10 years depresses the ability of various types of stem cells to renew tissue.

"Based on our earlier papers, the TGF-beta1 pathway seemed to be one of the main culprits in multi-tissue aging," said Conboy, an associate professor of bioengineering. "That one protein, when upregulated, ages multiple stem cells in distinct organs, such as the brain, pancreas, heart and muscle. This is really the first demonstration that we can find a drug that makes the key TGF-beta1 pathway, which is elevated by aging, behave younger, thereby rejuvenating multiple organ systems."

The UC Berkeley team reported its results in the current issue of the journal Oncotarget. Conboy and Schaffer are members of a consortium of faculty who study aging within the California Institute for Quantitative Biosciences (QB3).

Depressed stem cells lead to aging

Aging is ascribed, in part, to the failure of adult stem cells to generate replacements for damaged cells and thus repair the body's tissues. Researchers have shown that this decreased stem cell activity is largely a result of inhibitory chemicals in the environment around the stem cell, some of them dumped there by the immune system as a result of chronic, low-level inflammation that is also a hallmark of aging.

In 2005, Conboy and her colleagues infused old mice with blood from young mice -- a process called parabiosis -- reinvigorating stem cells in the muscle, liver and brain/hippocampus and showing that the chemicals in young blood can actually rejuvenate the chemical environment of aging stem cells. Last year, doctors began a small trial to determine whether blood plasma from young people can help reverse brain damage in elderly Alzheimer's patients.

Such therapies are impractical if not dangerous, however, so Conboy, Schaffer and others are trying to track down the specific chemicals that can be used safely and sustainably for maintaining the youthful environment for stem cells in many organs. One key chemical target for the multi-tissue rejuvenation is TGF-beta1, which tends to increase with age in all tissues of the body and which Conboy showed depresses stem cell activity when present at high levels.

Five years ago, Schaffer, who studies neural stem cells in the brain, teamed up with Conboy to look at TGF-beta1 activity in the hippocampus, an area of the brain important in memory and learning. Among the hallmarks of aging are a decline in learning, cognition and memory. In the new study, they showed that in old mice, the hippocampus has increased levels of TGF-beta1 similar to the levels in the bloodstream and other old tissue.

Using a viral vector that Schaffer developed for gene therapy, the team inserted genetic blockers into the brains of old mice to knock down TGF-beta1 activity, and found that hippocampal stem cells began to act more youthful, generating new nerve cells.

Drug makes old tissue cleverer

The team then injected into the blood a chemical known to block the TGF-beta1 receptor and thus reduce the effect of TGF-beta1. This small molecule, an Alk5 kinase inhibitor already undergoing trials as an anticancer agent, successfully renewed stem cell function in both brain and muscle tissue of the same old animal, potentially making it stronger and more clever, Conboy said.

"The key TGF-beta1 regulatory pathway became reset to its young signaling levels, which also reduced tissue inflammation, hence promoting a more favorable environment for stem cell signaling," she said. "You can simultaneously improve tissue repair and maintenance repair in completely different organs, muscle and brain."

The researchers noted that this is only a first step toward a therapy, since other biochemical cues also regulate adult stem cell activity. Schaffer and Conboy's research groups are now collaborating on a multi-pronged approach in which modulation of two key biochemical regulators might lead to safe restoration of stem cell responses in multiple aged and pathological tissues.

"The challenge ahead is to carefully retune the various signaling pathways in the stem cell environment, using a small number of chemicals, so that we end up recalibrating the environment to be youth-like," Conboy said. "Dosage is going to be the key to rejuvenating the stem cell environment."

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2015年5月13日星期三

Seasonal immunity: Activity of thousands of genes differs from winter to summer -- ScienceDaily

The study, published in the journal Nature Communications, shows that the activity of almost a quarter of our genes (5,136 out of 22,822 genes tested) differs according to the time of year, with some more active in winter and others more active in summer. This seasonality also affects our immune cells and the composition of our blood and adipose tissue (fat).

Scientists have known for some time that various diseases, including cardiovascular disease, autoimmune diseases such as type 1 diabetes and multiple sclerosis, and psychiatric disorders, display seasonal variation, as does vitamin D metabolism. However, this is the first time that researchers have shown that this may be down to seasonal changes in how our immune systems function.

"This is a really surprising -- and serendipitous -- discovery as it relates to how we identify and characterise the effects of the susceptibility genes for type 1 diabetes," says Professor John Todd, Director of the JDRF/Wellcome Trust Diabetes and Inflammation Laboratory. "In some ways, it's obvious -- it helps explain why so many diseases, from heart disease to mental illness, are much worse in the winter months -- but no one had appreciated the extent to which this actually occurred. The implications for how we treat disease like type 1 diabetes, and even how we plan our research studies, could be profound."

An international team, led by researchers from the JDRF/Wellcome Trust Diabetes and Inflammation Laboratory in the Department of Medical Genetics, Cambridge Institute for Medical Research, examined samples from over 16,000 people living in both the northern and southern hemispheres, in countries including the UK, USA, Iceland, Australia and The Gambia. These samples included a mixture of blood samples and adipose tissue.

The researchers used a variety of techniques to study the samples, including looking at the cell types found in the blood and measuring the level of expression of the individuals' genes -- a gene is said to be 'expressed' when it is active in a particular cell or tissue, usually involving the generation of proteins. They found that the thousands of genes were expressed differently in blood and adipose tissue depending on what time of year the samples were taken. Similarly, they identified seasonal differences in the types of cells found in the blood.

Seasonal differences were present across mixed populations in geographically and ethnically diverse locations -- but the seasonal genes displayed opposing patterns in the northern and southern hemispheres. However, the pattern of seasonal activity was not reflected as strongly in Icelandic donors. The researchers speculate that this may be due to the near-24 hour daylight during summer and near-24 hour darkness in winter.

One gene of particular interest was ARNTL, which was more active in the summer and less active in the winter. Previous studies have shown that, in mice at least, the gene suppresses inflammation, the body's response to infection; if the gene has the same function in humans, then levels of inflammation will be higher during winter in the northern hemisphere. Inflammation is a risk factor for a range of diseases and hence in winter, those at greatest risk will likely reach the 'threshold' at which the disease becomes a problem much sooner. Drugs that target the mechanisms behind inflammation could offer a way of helping treat these diseases more effectively during the winter periods.

A particularly surprising finding was that a set of genes associated to an individual's response to vaccination was more active in winter, suggesting that some vaccination programmes might be more effective if carried out during winter months when the immune system is already 'primed' to respond.

During European and Australian winters, they argue, the thresholds required to trigger an immune response may be lower as a direct consequence of our coevolution with infectious organisms, which tend to be more prevalent during winter. Interestingly, people from The Gambia showed distinct seasonal variation in the numbers of immune cells in the blood that correlated with the rainy season (June-October), during which time infectious diseases, particularly mosquito-borne diseases such as malaria, are more rife.

"We know that humans adapt to changing environments," says Dr Chris Wallace. "Our paper suggests that human immune systems adapt to show different seasonal variation in equatorial regions with fewer distinct seasons compared to regions at higher and lower latitudes with more pronounced differences between winter and season."

It is not clear yet what mechanism maintains the seasonal variation seen in the immune system, though it may be due to environmental cues such as daylight and ambient temperature. Our internal body clock -- known as our circadian rhythm -- is in part coordinated by changes in daylight, which explains why people in jobs that do not fit with the daily cycle, such as factory shift workers or crews on long haul flights, can be affected by poorer health.

Professor Todd adds: "Given that our immune systems appear to put us at greater risk of disease related to excessive inflammation in colder, darker months, and given the benefits we already understand from vitamin D, it is perhaps understandable that people want to head off for some 'winter sun' to improve their health and well-being."

The research was funded by the Wellcome Trust, the type 1 diabetes charity JDRF and the NIHR Cambridge Biomedical Research Centre.

Professor Mike Turner, Head of Infection and Immunobiology at the Wellcome Trust said: "This is an excellent study which provides real evidence supporting the popular belief that we tend to be healthier in the summer. Seasonal variation to this extent is a fascinating find -- the activity of many of our genes, as well as the composition of our blood and fat tissue, varies depending on the seasons. Although we are still unclear of the mechanism that governs this variation, one possible outcome is that treatment for certain diseases could be more effective if tailored to the seasons."

Karen Addington, Chief Executive of JDRF in the UK, said: "We have long known there are more diagnoses of type 1 diabetes in winter. This study begins to reveal why. It identifies a biological mechanism we didn't previously know of, which leaves the body seasonally more prone to the autoimmune attack seen in type 1 diabetes.

"While we all love winter sun, flying south for the whole of each winter isn't something anyone can practically recommend as a way of preventing type 1 diabetes. But this new insight does open new avenues of research that could help untangle the complex web of genetic and environmental factors behind a diagnosis."

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Breakthrough in tinnitus research could lead to testable model -- ScienceDaily

Tinnitus is largely a mystery, a phantom sound heard in the absence of actual sound. Tinnitus patients "hear" ringing, buzzing or hissing in their ears much like an amputee might "feel" pain in a missing limb. It is a symptom, not a disease, and though exposure to loud noise may cause it, some cases have no apparent trigger.

Existing treatments, meantime, are unreliable, either not working at all or varying greatly in effectiveness for those who report some relief.

But a global research effort involving investigators from the University at Buffalo; Southeast University in Nanjing, China; and Dalhousie University in Nova Scotia, Canada, have made a major breakthrough that provides new insights into how tinnitus, and the often co-occurring hyperacusis, a condition that causes sounds to be perceived as intolerably loud, might develop and be sustained.

The results of the study, to be published in a forthcoming edition of eLife, suggest the neural network responsible is more expansive than previously thought. The findings could lead to a testable model that helps to identify what region or regions of the brain might be responsible for causing the two conditions.

Having conceptualized a broader, more comprehensive neural network, the researchers hope to eventually test the model by deactivating specific segments of the neural network. By process of elimination they would learn if shutting down one part of that network relieves tinnitus, hyperacusis or both conditions.

Until the mid-1990s, tinnitus was thought to be centered in the ear, but patients who lost their hearing on one side after a surgical tumor removal unrelated to the condition reported still hearing a ringing -- in their deaf ear.

"This changed the thinking in the field," says Richard Salvi, director of UB's Center for Hearing and Deafness, and one of the study's authors. "Having severed the neural connection between the ear and the brain, it's impossible for the phantom sound to be generated in the ear. It has to be generated in the brain."

Though it's not known yet exactly where and how tinnitus occurs in the brain, Salvi says their functional MRI studies show the abnormal activity underlying tinnitus and hyperacusis isn't confined to a specific brain location, but actually involves a neural network.

Unlike traditional MRIs, which show only structure, functional MRIs show what parts of the structure are active at a given time while functional connectivity MRI reveals how one part of the brain interacts with other regions, much like partners would interact on a dance floor, explains Yu-Chen Chen, a radiologist at Southeast University and one of the study's co-authors.

The researchers induced tinnitus in rats by administering the active ingredient in aspirin, which has long been known to produce tinnitus and hyperacusis symptoms in humans.

"Certain brain regions become very active once tinnitus is induced, much more so than it is for an animal with normal hearing," says Salvi. "Even though high-dose aspirin induces a hearing loss and less information is being sent from the ear to the brain as a result, the brain responds with greater activity. It's paradoxical, like a car getting better gas mileage with a less efficient engine."

Tracing the network's course, the investigators identified a major hub within the central auditory pathway, the sound processing center of the brain.

"Other research has shown this activity, but what is novel about the current study is the amygdala pops up. This is the part of the brain that assigns emotion to our perceptions," says Salvi. "Many patients report the onset of tinnitus after experiencing significant stress or anxiety. We think it's not just the hearing loss that's essential. There are other emotional factors working together with the auditory factors."

The reticular formation, an arousal center involved in the "fight or flight" response is active too, plus the hippocampus, the memory region of the brain that helps identify where things are located, such as the location of the phantom sound. So the auditory system is connecting sound to a location, the ear in this case. There is emotion and arousal, but the final puzzling piece to the network is activity in the cerebellum, normally activated during motor planning events like reaching for a cup or catching a ball.

"We were shocked when this part of the brain popped up," says Salvi. "Almost all parts of the network can be explained: location of sound; the emotional attachment; why people get aroused when they have tinnitus; we're puzzled by the cerebellum involvement, but it might act like some kind of "gate" that's allowing the phantom sound to enter the consciousness," says Salvi.

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Male hormones help lemur females rule -- ScienceDaily

Males rule in most of the animal world. But when it comes to conventional gender roles, lemurs -- distant primate cousins of ours -- buck the trend.

It's not uncommon for lady lemurs to bite their mates, snatch a piece of fruit from their hands, whack them in the head or shove them out of prime sleeping spots. Females mark their territories with distinctive scents just as often as the males do. Males often don't take their share of a meal until the females have had their fill.

"If a male lemur is enjoying a patch of sunlight, for example, a female is likely to push him aside and take his spot," said Joseph Petty, most recently a doctoral student at Duke University.

Most female mammals that get their way over males are well-armed to be the bullies. Dominant female spotted hyenas, for example, are bigger and heavier than males.

But female dominance in lemurs remains a puzzle. Female lemurs are no bigger than males, and they don't have antlers or bigger fangs to give them a physical edge over their mates.

Researchers at the Duke Lemur Center say females have significantly lower testosterone levels than the males across the board. But when they compared six lemur species, they found that females of some species have higher testosterone levels than others.

Petty and Duke professor of evolutionary anthropology Christine Drea examined behavior and hormone profiles in nearly 30 animals representing six closely-related species in the genus Eulemur. In four of the species, females are at the top of the pecking order, and in the other two species the sexes have equal status.

The dominant females had significantly higher male hormone levels than the females from the two more egalitarian species.

"It's strong evidence that hormones are playing a role," Petty said.

Lemurs and lorises split off from the rest of the primate family tree more than 60 million years ago, but the two species of egalitarian lemurs didn't evolve until much more recently, within the last 2 million years.

It could be that females are more sensitive to the effects of testosterone than males, stimulating aggressive behavior even though males still have more of the hormone, Petty said.

The results appear online in the journal Scientific Reports. This work was supported by grants from the National Science Foundation (IOS-0719003, IOS-1021633, BCS 1341150) and by the Margot Marsh Biodiversity Foundation.

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A metal composite that will (literally) float your boat -- ScienceDaily

Although syntactic foams have been around for many years, this is the first development of a lightweight metal matrix syntactic foam. It is the work of a team of researchers from Deep Springs Technology (DST) and the New York University Polytechnic School of Engineering.

Their magnesium alloy matrix composite is reinforced with silicon carbide hollow particles and has a density of only 0.92 grams per cubic centimeter compared to 1.0 g/cc of water. Not only does it have a density lower than that of water, it is strong enough to withstand the rigorous conditions faced in the marine environment.

Significant efforts in recent years have focused on developing lightweight polymer matrix composites to replace heavier metal-based components in automobiles and marine vessels. The technology for the new composite is very close to maturation and could be put into prototypes for testing within three years. Amphibious vehicles such as the Ultra Heavy-lift Amphibious Connector (UHAC) being developed by the U.S. Marine Corps can especially benefit from the light weight and high buoyancy offered by the new syntactic foams, the researchers explained.

"This new development of very light metal matrix composites can swing the pendulum back in favor of metallic materials," forecasted Nikhil Gupta, an NYU School of Engineering professor in the Department of Mechanical and Aerospace Engineering and the study's co-author. "The ability of metals to withstand higher temperatures can be a huge advantage for these composites in engine and exhaust components, quite apart from structural parts."

The syntactic foam made by DST and NYU captures the lightness of foams, but adds substantial strength. The secret of this syntactic foam starts with a matrix made of a magnesium alloy, which is then turned into foam by adding strong, lightweight silicon carbide hollow spheres developed and manufactured by DST. A single sphere's shell can withstand pressure of over 25,000 pounds per square inch (PSI) before it ruptures -- one hundred times the maximum pressure in a fire hose. The hollow particles also offer impact protection to the syntactic foam because each shell acts like an energy absorber during its fracture. The composite can be customized for density and other properties by adding more or fewer shells into the metal matrix to fit the requirements of the application. This concept can also be used with other magnesium alloys that are non-flammable.

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Astronomy: Delta Cephei has a hidden companion -- ScienceDaily

A secret companion

As the scientists from Geneva and Baltimore measured Delta Cephei's pulsations with the Hermes spectrograph, installed at the Mercator telescope based on La Palma, one of the Canary Islands, an unexpected signal was detected. Using high-precision Doppler spectroscopy (developed and used for researching exoplanets), the researchers discovered that the speed with which Delta Cephei approaches the Sun is not constant, but changes with time in a characteristic fashion. This change of speed can only be explained by the presence of another star, which orbits around Delta Cephei. In other words, there is a secret companion, whose existence we did not suspect. By combining their own observations with data from the scientific literature, the researchers determined the orbit of the two stars and observed that the mass of the companion is low (around 10 times lower than the mass of Delta Cephei).

"We were shocked: despite all the attention Delta Cephei was given over the years, we were lacking an essential piece of information," states Richard Anderson, researcher at UNIGE at the time of the discovery, first author of the article and now researcher at Johns Hopkins University, in the United States.

According to the scientists, the data collected in the framework of ESA's Gaia space mission will enable Delta Cephei's orbit to be precisely measured. The presence of the companion must consequently be taken into account when the Gaia team determines the Delta Cephei's distance.

"Although our study does not challenge the cosmic distance ladder as a whole, improving the precision of every one of its rungs will eventually benefit cosmology," explains Richard Anderson. "This discovery reminds us that something is always to be learned. If even one of the closest Cepheids is keeping such secrets , who knows what we will discover about the ones furthest from us!"

A turbulent past?

Due to its excentric orbit, Delta Cephei is sometimes further and sometimes closer to its companion. This suggests a very dynamic evolution, since the two stars are approaching each other to within twice the Earth-Sun distance (astronomical unit) every 6 years, which is a small distance for a Supergiant star such as Delta Cephei whose radius is 43 times larger than that of the Sun. Delta Cephei's excentric orbit thus points to interactions between the two stars due to tidal forces that occur when they are close to each other. This could help the interpretation of other astronomers' work in the past, who have observed a strange circumstellar environment, for which no definitive explanation has been found yet.

This study is likely to inspire further research aiming to better understand the evolution of Delta Cephei, since binarity is an essential property to consider for interpreting the evolution of a star. Studying the evolution of Cepheids is particularly interesting, since it helps to improve the understanding of the structure and evolution of stars in general.

"We are waiting for the results from new measurements taken with the Hermes spectrograph and the observations from Gaia. These will allow us to precisely trace the possibly turbulent past of Delta Cephei," the astronomers anticipate. "It is a fascinating adventure!"

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