Tuesday, December 8, 2009


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What constitutes fish food is a matter of debate. A high-profile study a few years ago suggested that fish get almost 50 percent of their carbon from trees and leaves, evidence for a very close link between the terrestrial and aquatic ecosystems.
But new research from the University of Washington shows this is not likely to be true. Algae provide a much richer diet for fish and other aquatic life, according to research published this week in the Proceedings of the National Academy of Sciences.

"Are the fish made of maple? Our argument would be no, they're not, they're made of algae," says Michael Brett, a UW professor of civil and environmental engineering. "Other scientists have said that up to 50 percent of the carbon was coming from this terrestrial source. We're saying that's very unlikely."

The results could be important not just to fish but to people seeking to boost fish populations.

"In terms of fishery production this means you've really got to focus on the algae," Brett said. "The terrestrial environment is still important, but for other reasons such as habitat."

The new paper shows that algae are necessary ingredients for healthy zooplankton, the animals at the base of the aquatic food web. Brett's lab studies omega-3 fatty acids, the same ones touted in health studies. Fish can't produce the heart-healthy lipids, they just accumulate them from their diet. Brett's group looks at where exactly the omega-3's are coming from, largely from several groups of phytoplankton that can make these fats.

After reading the fish food study published in 2004 in the journal Nature, "we were furrowing our brows and saying 'This doesn't make sense,'" Brett said, "because the terrestrial plants aren't producing these omega-3 molecules. Those results completely conflicted with the perspective that was coming out of our own area of research."

The earlier study by the Institute for Ecosystem Studies in Millbrook, N.Y., was a large-scale experiment on three lakes in Michigan. Researchers fertilized these lakes with a labeled form of carbon dioxide sprinkled on the lakes' surfaces over more than a month. They then analyzed how much of that labeled carbon showed up in animals at each position in the aquatic food web. Even when terrestrial plant matter was only about 20 percent of the available food, they found, the animals appeared to be composed of about 50 percent land-based carbon.

The UW study took a different approach. Brett and colleagues raised zooplankton in the lab, feeding them a diet of either pure algae, pure land-based carbon, or various mixtures of the two. They found that zooplankton fed a purely land-based diet survived and reproduced but were small and produced relatively few offspring. Zooplankton fed a diet of pure algae were 10 times bigger than their tree-fed twins and produced 20 times more offspring. Zooplankton fed a mixed diet were larger and produced more offspring as the proportion of algae in their diet went up. Even when zooplankton ate almost nothing but land-based carbon, nearly all their lipids came from algae.

"I think we were able to show that the terrestrial source is such low quality that it's inconceivable that it could be nearly as important as what that study suggested," Brett said.

The research was funded by the National Science Foundation. Co-authors are Martin Kainz of the Danube University Krems in Austria and Sami Taipale and Hari Seshan of the UW.

So why did the earlier study suggest that fish were eating land-based food? Brett believes the reason is those researchers discounted the idea of zooplankton migration, the daily movement down to deeper waters during the daytime to hide from predatory fish. Researchers sprinkled tagged food in the upper waters and assumed that any other food source must be land-based.

"The flaw was that there was an alternative source. They could have been getting half of their carbon from the lower depths in the lakes," Brett said.

In recent years the earlier study has had a profound impact on the field of aquatic ecology but few scientists have critically assessed its results, Brett says. "What I would hope our paper would do is to really get people to open their eyes and say 'Does this really add up, and is there a simpler way to look at what is supporting fisheries production?'"

(Photo: University of Washington)

University of Washington


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Scientists at the California Institute of Technology (Caltech) have uncovered evidence of a primitive emotion-like behavior in the fruit fly, Drosophila melanogaster.

Their findings, which may be relevant to the relationship between the neurotransmitter dopamine and attention deficit hyperactivity disorder (ADHD), are described in the December issue of the journal Neuron.

The Drosophila brain contains only about 20,000 neurons and has long been considered a powerful system with which to study the genetic basis of behaviors such as learning and courtship, as well as memory and circadian rhythms. What hasn't been clear is whether the Drosophila brain also could be used to study the genetic basis of "emotional" behaviors.

"Such studies are important," says David Anderson, Caltech's Seymour Benzer Professor of Biology and a Howard Hughes Medical Institute investigator, "because it's believed that abnormalities in these types of behaviors may underlie many psychiatric disorders."

Most of the genes found in the fruit fly—more accurately referred to as the vinegar fly—are found in humans as well, including those neurons that produce brain chemicals like dopamine and serotonin, which have been implicated in psychiatric disorders.

In their Neuron paper, the Caltech team—led by postdoctoral fellow Tim Lebestky—found that a series of brief but brisk air puffs, delivered in rapid succession, caused flies to run around their test chamber in what Anderson calls a "frantic manner." This behavior persisted for several minutes after the last of the puffs.

"Even after the flies had 'calmed down,'" he adds, "they remained hypersensitive to a single air puff."

To quantify the flies' behavior, Anderson's group collaborated with Pietro Perona, the Allen E. Puckett Professor of Electrical Engineering at Caltech. Together with his students, Perona developed an automated machine-vision-based system to track the movement of the flies, and derived a simple mathematical model to fit the movement data and to extract metrics that described various aspects of the flies' responses under different conditions.

The researchers used this test to search for flies with an abnormally exaggerated hyperactivity response; genetic studies of these flies revealed that a mutation in a dopamine receptor (a mutation that eliminates the receptor) produced the aberrant behavior. Flies with this dopamine-receptor mutation were hypersensitive to the air puffs, and took much longer to calm down than did "normal" flies without the mutation.

What is surprising about this result, notes Lebestky, “is that previous studies in both flies and vertebrates had suggested that dopamine promotes activity, but our experiments uncovered a function of dopamine in the opposite direction." Because removing the receptor causes hypersensitivity to the air puffs, these results “suggested that dopamine actively inhibits the hyperactivity response,” Lebestky says.

This observation suggested a possible link to ADHD, a behavioral disorder characterized by impulsivity, hyperactivity, and short attention span. Humans with the disorder often take drugs, such as Ritalin, that increase levels of brain dopamine in order to reduce hyperactivity.

The ways the mutant flies respond to the air puffs is, moreover, "reminiscent of the way in which individuals with ADHD display hypersensitivity to environmental stimuli and are more easily aroused by such influences," says Anderson. Importantly, ADHD has been genetically linked to abnormalities of the dopamine system in humans, further strengthening the analogy between the mutant flies and this psychiatric disorder.

There is also another possible link: some individuals with ADHD display learning disabilities. Similarly, researchers from Pennsylvania State University—who collaborated on the Neuron study—have shown previously that flies with the same dopamine receptor mutation are unable to learn to associate a particular odor with an electric shock, and do not avoid the odor when subsequently tested. (Flies without the mutation quickly learn to make the association.)

It is often assumed that because individuals with ADHD are hyperactive and easily distracted, they have difficulty learning. The Caltech group showed, however, that hyperactivity and learning disabilities are not causally related in flies bearing the dopamine receptor mutation, thereby disproving the theory—at least in flies.

"We could separately 'rescue' the hyperactivity and learning deficits in a completely independent manner," says Anderson, "by genetically restoring the dopamine receptor to different regions of the fly's brain."

Thus, in dopamine-receptor-mutant flies, hyperactivity does not seem to cause learning deficits. Instead, these two "symptoms" reflect independent effects of the mutation that manifest themselves in distinct brain regions. "Being able to observe and manipulate the different neural substrates for learning and arousal will hopefully give us a unique method for identifying new molecular pathways that could be investigated and validated in higher organisms," says Lebestky.

This finding in flies, notes Anderson, raises the possibility that hyperactivity and learning deficits also may not be causally linked in humans with ADHD. If so, he says, it ultimately may prove more effective to develop drugs to treat these two symptoms separately, rather than trying to cure them both with the broad-spectrum pharmaceuticals currently available, which have many undesirable side effects.

"The finding that flies exhibit emotion-like behaviors that are controlled by some of the same brain chemicals as in humans opens up the possibility of applying the powerful genetics of this 'model organism' to understanding how these chemicals influence behavior through their actions on specific brain circuits," says Anderson. "While the specific details of where and how this occurs are likely to be different in flies and in humans, the basic principles are likely to be evolutionarily conserved, and may aid in our understanding of what goes wrong in disorders such as ADHD."

California Institute of Technology (Caltech)


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A cancer vaccine carried into the body on a carefully engineered, fingernail-sized implant is the first to successfully eliminate tumors in mammals, scientists report in the journal Science Translational Medicine.

The new approach, pioneered by bioengineers and immunologists at Harvard University, uses plastic disks impregnated with tumor-specific antigens and implanted under the skin to reprogram the mammalian immune system to attack tumors. The journal article describes the use of such implants to eradicate melanoma tumors in mice.

“This work shows the power of applying engineering approaches to immunology,” said David J. Mooney, the Robert P. Pinkas Family Professor of Bioengineering in Harvard’s School of Engineering and Applied Sciences and Wyss Institute for Biologically Inspired Engineering. “By marrying engineering and immunology through this collaboration with Glenn Dranoff at the Dana-Farber Cancer Institute, we’ve taken a major step toward the design of effective cancer vaccines.”

Most cancer cells easily skirt the immune system, which operates by recognizing and attacking invaders from outside the body. The approach developed by Mooney’s group redirects the immune system to target tumors, and appears both more effective and less cumbersome than other cancer vaccines currently in clinical trials.

Conventional cancer vaccinations remove immune cells from the body, reprogram them to attack malignant tissues, and return them to the body. However, more than 90 percent of reinjected cells die before having any effect in experiments.

The slender implants developed by Mooney’s group measure 8.5 millimeters in diameter and are made of an FDA-approved biodegradable polymer. Ninety percent air, the disks are highly permeable to immune cells and release cytokines, powerful recruiters of immune-system messengers called dendritic cells.

These cells enter an implant’s pores, where they are exposed to antigens specific to the type of tumor being targeted. The dendritic cells then report to nearby lymph nodes, where they direct the immune system’s T cells to hunt down and kill tumor cells.

“Inserted anywhere under the skin — much like the implantable contraceptives that can be placed in a woman’s arm — the implants activate an immune response that destroys tumor cells,” Mooney said.

The technique may have powerful advantages over surgery and chemotherapy, and may also be useful in combination with existing therapies. It only targets tumor cells, avoiding collateral damage elsewhere in the body. And, much as an immune response to a bacterium or virus generates long-term resistance, researchers anticipate that cancer vaccines will generate permanent and bodywide resistance against cancerous cells, providing durable protection against relapse.

Mooney said the new approach’s strength lies in its ability to simultaneously regulate the two arms of the human immune system: one that destroys foreign material, and one that protects tissue native to the human body. The implant-based vaccine recruits several types of dendritic cells that direct destructive immune responses, creating an especially potent anti-tumor response.

“This approach is able to simultaneously upregulate the destructive immune response to the tumor while downregulating the arm of the immune system that leads to tolerance,” Mooney said. “In cancer, this latter arm is typically a limiting feature of immunotherapies, since it can extinguish vaccine activity and afford tumors a degree of protection.”

(Photo: Omar Ali/Harvard University)

Harvard University


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Of all global carbon dioxide emissions, less than half accumulate in the atmosphere where it contributes to global warming. The remainder is hidden away in oceans and terrestrial ecosystems such as forests, grasslands and peat-lands. Stimulating this "free service" of aquatic and terrestrial ecosystems is considered one of the main, immediately available ways of reducing climate change. However, new greenhouse gas bookkeeping has revealed that for the European continent this service isn’t free after all. These findings are presented in the most recent edition of Nature Geoscience (Advanced Online Publication, November 22, 2009).

Researchers from 17 European countries cooperating in the EU-Integrated Project CarboEurope, led by Detlef Schulze, of the Max Planck Institute for Biogeochemistry in Jena, Germany have compiled the first comprehensive greenhouse gas balance of Europe. They made two independent estimates: one based on what the atmosphere sees and one based on what terrestrial ecosystems see.

The new bookkeeping effort confirmed the existence of a strong carbon sink of -305 Million tonnes of carbon per year in European forests and grasslands. A sink of this magnitude could offset 19% of the emission from fossil fuel burning. However, agricultural land and drained peat-land are emitting CO2, which cancels part of this sink. The resulting net CO2 sink of the European continent is 274 Million tonnes of carbon per year - only 15% of the emissions from fossil fuel burning. But this balance is still incomplete, because all European ecosystems are managed and as a by-product of land management other powerful greenhouse gases are released - for example nitrous oxide from fertilizers applied to grassland and crops, and methane from ruminants and from peat-lands. These previously neglected emissions of greenhouse gases from land-use cancel out almost the entire carbon sink, leaving the landscape offsetting only some 2% of the CO2 emissions from households, transport and industry.

Compared to Europe as a whole, the situation is even worse for the 25 states of the European Union. Here, although forests and grasslands can compensate for 13% of the CO2 emitted by fossil fuel burning, emission of powerful greenhouse gases from agricultural emissions and peat mining reduces the effectiveness of the land surface sink to 111 Million tonnes of carbon per year, which is only 11% of the CO2 emitted by fossil fuels. However, since the emissions of methane and nitrous oxide are relatively higher in the European Union the land surface emerges as a greenhouse gas source of 34 Million tonnes of carbon per year. This effectively increases the emissions from fossil fuel burning by another 3%.

Prof Schulze said "These findings show that if the European landscape is to contribute to mitigating global warming, we need a new, different emphasis on land management. Methane and nitrous oxide are such powerful greenhouse gases; we must manage the landscape to decrease their emissions."

(Photo: CarboEurope Team)

Max Planck Society


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Sometimes you really can believe your eyes. That's what NASA's Solar Terrestrial Relations Observatory (STEREO) is telling researchers about a controversial phenomenon on the sun known as the "solar tsunami."

Years ago, when solar physicists first witnessed a towering wave of hot plasma racing across the sun's surface, they doubted their senses. The scale of the wave was staggering: It rose up higher than Earth itself and rippled out from a central point in a circular pattern millions of kilometers in circumference. Skeptical observers suggested it might be a shadow of some kind—a trick of the satellite's eye—but surely not a real wave.

"Now we know," says Joe Gurman of the Solar Physics Laboratory at NASA's Goddard Space Flight Center. "Solar tsunamis are real."

The twin STEREO spacecraft confirmed their reality in February 2009 when sunspot 11012 unexpectedly erupted. The blast hurled a billion-ton cloud of gas (a coronal mass ejection, or CME) into space and sent a tsunami racing along the sun's surface. STEREO recorded the wave from two positions separated by 90 degrees, giving researchers an unprecedented view of the event.

"It was definitely a wave," says Spiros Patsourakos of George Mason University, lead author of a paper reporting the finding in Astrophysical Journal Letters. "Not a wave of water, but a giant wave of hot plasma and magnetism."

The technical name is "fast-mode magnetohydrodynamical wave," or "MHD wave" for short. The one STEREO saw reared up about 100,000 kilometers high, raced outward at 250 km/second (560,000 mph), and packed as much energy as 2400 megatons of TNT (1029 ergs).

Solar tsunamis were discovered in 1997 by the Solar and Heliospheric Observatory (SOHO). In May of that year, a CME came blasting up from an active region on the sun's surface, and SOHO recorded a tsunami rippling away from the blast site.

"We wondered," recalls Gurman, "is that a wave, or just a shadow of the CME overhead?"

SOHO's single point of view was not enough to answer the question—neither for that first wave nor for many similar events recorded by SOHO in years that followed.

The question remained open until after the launch of STEREO. At the time of the February 2009 eruption, STEREO-B was directly over the blast site, while STEREO-A was stationed at a right angle —"perfect geometry for cracking the mystery," says co-author Angelos Vourlidas of the Naval Research Laboratory in Washington, D.C.

The physical reality of the waves has been further confirmed by movies of the waves crashing into things. "We've seen the waves reflected by sunspots," says Vourlidas. "And there is a wonderful movie of a solar prominence oscillating after it gets hit by a wave. We call it the 'dancing prominence.'"

Solar tsunamis pose no direct threat to Earth, but they are important to study. "We can use them to diagnose conditions on the sun," notes Gurman. "By watching how the waves propagate and bounce off things, we can gather information about the sun's lower atmosphere available in no other way."

"Tsunami waves can also improve our forecasting of space weather," adds Vourlidas, "Like a bull-eye, they 'mark the spot' where an eruption takes place. Pinpointing the blast site can help us anticipate when a CME or radiation storm will reach Earth."

And they're pretty entertaining, too. "The movies," he says, "are out of this world."

(Photo: NASA)



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The first large black holes in the universe likely formed and grew deep inside gigantic, starlike cocoons that smothered their powerful x-ray radiation and prevented surrounding gases from being blown away, says a new study led by the University of Colorado at Boulder.

The formation process involved two stages, said Mitchell Begelman, a professor and the chair of CU-Boulder's astrophysical and planetary sciences department. The predecessors to black hole formation, objects called supermassive stars, probably started forming within the first few hundred million years after the Big Bang some 14 billion years ago. A supermassive star eventually would have grown to a huge size -- as much as tens of millions of times the mass of our sun -- and would have been short-lived, with its core collapsing in just in few million years, he said.

In the new study to be published in Monthly Notices of the Royal Astronomical Society in London, Begelman calculated how supermassive stars might have formed, as well as the masses of their cores. These calculations allowed him to estimate their subsequent size and evolution, including how they ultimately left behind "seed" black holes.

Begelman said the hydrogen-burning supermassive stars would had to have been stabilized by their own rotation or some other form of energy like magnetic fields or turbulence in order to facilitate the speedy growth of black holes at their centers. "What's new here is we think we have found a new mechanism to form these giant supermassive stars, which gives us a new way of understanding how big black holes may have formed relatively fast," said Begelman.

The main requirement for the formation of supermassive stars is the accumulation of matter at a rate of about one solar mass per year, said Begelman. Because of the tremendous amount of matter consumed by supermassive stars, subsequent seed black holes that formed in their centers may have started out much bigger than ordinary black holes -- which are the mass of only a few Earth suns -- and subsequently grew much faster.

After the seed black holes formed, the process entered its second stage, which Begelman has dubbed the "quasistar" stage. In this phase, black holes grew rapidly by swallowing matter from the bloated envelope of gas surrounding them, which eventually inflated to a size as large as Earth's solar system and cooled at the same time, he said.

Once quasistars cooled past a certain point, radiation began escaping at such a high rate that it caused the gas envelope to disperse and left behind black holes up to 10,000 times or more the mass of Earth's sun, Begelman said. With such a big head start over ordinary black holes, they could have grown into supermassive black holes millions or billions of times the mass of the sun either by gobbling up gas from surrounding galaxies or merging with other black holes in extremely violent galactic collisions.

The quasistar phase was analyzed in a 2008 paper published by Begelman in collaboration with CU Professor Phil Armitage and Research Associate Elena Rossi.

"Until recently, the thinking by many has been that supermassive black holes got their start from the merging of numerous, small black holes in the universe," he said. "This new model of black hole development indicates a possible alternate route to their formation."

Black holes are extremely dense celestial objects believed to be formed by the collapse of stars and which have such a strong gravitational field that nothing, not even light, can escape. While black holes are not directly detectable by astronomers, the movement of stellar matter swirling around them and powerful jets of gas blasting outward provides evidence for their existence. Ordinary black holes are thought to be remnants of stars slightly larger than our sun that used up their fuel and died, he said.

The supermassive black holes created early in the history of the universe may have gone on to produce the phenomenon of quasars -- the very bright, energetic centers of distant galaxies that can be a trillion times brighter than our sun. There also is evidence that a supermassive black hole inhabits the center of every massive galaxy today, including our own Milky Way, said Begelman.

"Big black holes formed via these supermassive stars could have had a huge impact on the evolution of the universe, including galaxy formation," he said. Begelman is collaborating with University of Michigan astrophysicist Marta Volonteri, comparing the possible formation of supermassive black holes from supermassive stars and quasistars versus their creation by the merging of ordinary black holes left behind by the collapse of the universe's earliest stars.

Scientists may be able to use NASA's James Webb Space Telescope, slated for launch in 2013, to look back in time and hunt for the cocoon-like supermassive stars near the edges of the early universe, which would shine brightly in the near infrared portion of the electromagnetic spectrum, said Begelman.

(Photo: University of Colorado at Boulder)

University of Colorado at Boulder




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