Thursday, November 4, 2010

STUDY SHOWS POLLINATORS CAN DRIVE EVOLUTION OF FLOWER TRAITS

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Pretty flowers aren't produced so we can show them off in vases -- they serve the purpose of attracting such pollinators as bees, butterflies and hummingbirds, which enable them to produce seeds for the next generation.

Now, confirming scientists' assumptions for years, a new Cornell study has proven that such pollinators are agents of natural selection in flowers -- at least in the foxglove beardtongue (Penstemon digitalis) plant.

"It was assumed that pollinators drive evolution on floral traits because pollinators prefer certain floral characteristics," said Andre Kessler, assistant professor of ecology and evolutionary biology and senior author of a paper published recently in the journal New Phytologist. "In this species, we found that pollinators are the agents of selection on flower morphology [a flower's physical characteristics]," he added.

"These findings are important because it is only by understanding the agents of natural selection that we understand why evolutionary change occurs," said Amy Parachnowitsch, Ph.D. '10, the paper's lead author and a former graduate student in Kessler's lab.

To test their theories, the researchers allowed bees and other insects to pollinate the flowers of 150 beardtongues in a field; they also hand-pollinated every flower on another 150 plants in the same field. Since the hand-pollinated plants were not dependent on pollinators, they acted as a baseline of natural selection by other forces to which open-pollinated plants could be compared. The researchers could then assess whether pollinators were exerting natural selection on seven floral traits tested by comparing the open-pollinated with hand-pollinated plants. If pollinators were driving natural selection on floral traits, then they would have found stronger selection in the open-pollinated plants.

In fact, they found that insect- or open-pollinated plants showed statistically stronger selection for two traits: larger and more flowers. The results definitively showed that pollinators were the agents of selection for both these traits.

The researchers also found that for the number of flowers in open-pollinated plants, a phenomenon called stabilizing selection was at work -- just as it isn't good for human babies to be born too big or too small, it was best for plants to have an intermediate number of blossoms in the open-pollinated plants.

Common sense suggests it is always better to have more flowers because having more flowers often leads to more fruits and seeds. However, Kessler said there can be a cost for plants having too many large flowers -- lots of large, showy flowers boosts the odds that flowers end up pollinating other flowers on the same plant. Showy displays can also attract herbivores that eat both seeds and flowers.

The researchers suspect that the stabilizing selection by pollinators keeps the beardtongues from evolving to have ever-bigger displays and, thus, plants avoid inbreeding.

(Photo: Amy Parachnowitsch)

Cornell University

CARBON DIOXIDE CONTROLS EARTH'S TEMPERATURE

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Water vapor and clouds are the major contributors to Earth's greenhouse effect, but a new atmosphere-ocean climate modeling study shows that the planet's temperature ultimately depends on the atmospheric level of carbon dioxide.

The study, conducted by Andrew Lacis and colleagues at NASA's Goddard Institute for Space Studies (GISS) in New York, examined the nature of Earth's greenhouse effect and clarified the role that greenhouse gases and clouds play in absorbing outgoing infrared radiation. Notably, the team identified non-condensing greenhouse gases -- such as carbon dioxide, methane, nitrous oxide, ozone, and chlorofluorocarbons -- as providing the core support for the terrestrial greenhouse effect.

Without non-condensing greenhouse gases, water vapor and clouds would be unable to provide the feedback mechanisms that amplify the greenhouse effect. The study's results were published Friday, Oct. 15 in Science.

A companion study led by GISS co-author Gavin Schmidt that has been accepted for publication in the Journal of Geophysical Research shows that carbon dioxide accounts for about 20 percent of the greenhouse effect, water vapor and clouds together account for 75 percent, and minor gases and aerosols make up the remaining five percent. However, it is the 25 percent non-condensing greenhouse gas component, which includes carbon dioxide, that is the key factor in sustaining Earth’s greenhouse effect. By this accounting, carbon dioxide is responsible for 80 percent of the radiative forcing that sustains the Earth’s greenhouse effect.

The climate forcing experiment described in Science was simple in design and concept -- all of the non-condensing greenhouse gases and aerosols were zeroed out, and the global climate model was run forward in time to see what would happen to the greenhouse effect. Without the sustaining support by the non-condensing greenhouse gases, Earth’s greenhouse effect collapsed as water vapor quickly precipitated from the atmosphere, plunging the model Earth into an icebound state -- a clear demonstration that water vapor, although contributing 50 percent of the total greenhouse warming, acts as a feedback process, and as such, cannot by itself uphold the Earth's greenhouse effect.

"Our climate modeling simulation should be viewed as an experiment in atmospheric physics, illustrating a cause and effect problem which allowed us to gain a better understanding of the working mechanics of Earth’s greenhouse effect, and enabled us to demonstrate the direct relationship that exists between rising atmospheric carbon dioxide and rising global temperature," Lacis said.

The study ties in to the geologic record in which carbon dioxide levels have oscillated between approximately 180 parts per million during ice ages, and about 280 parts per million during warmer interglacial periods. To provide perspective to the nearly 1 C (1.8 F) increase in global temperature over the past century, it is estimated that the global mean temperature difference between the extremes of the ice age and interglacial periods is only about 5 C (9 F).

"When carbon dioxide increases, more water vapor returns to the atmosphere. This is what helped to melt the glaciers that once covered New York City," said co-author David Rind, of NASA's Goddard Institute for Space Studies. "Today we are in uncharted territory as carbon dioxide approaches 390 parts per million in what has been referred to as the 'superinterglacial.'"

"The bottom line is that atmospheric carbon dioxide acts as a thermostat in regulating the temperature of Earth," Lacis said. "The Intergovernmental Panel on Climate Change has fully documented the fact that industrial activity is responsible for the rapidly increasing levels of atmospheric carbon dioxide and other greenhouse gases. It is not surprising then that global warming can be linked directly to the observed increase in atmospheric carbon dioxide and to human industrial activity in general."

(Photo: NASA GISS/ Lilly Del Valle)

NASA

CLIMATE CHANGE: DROUGHT MAY THREATEN MUCH OF GLOBE WITHIN DECADES

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The United States and many other heavily populated countries face a growing threat of severe and prolonged drought in coming decades, according to a new study by National Center for Atmospheric Research (NCAR) scientist Aiguo Dai. The detailed analysis concludes that warming temperatures associated with climate change will likely create increasingly dry conditions across much of the globe in the next 30 years, possibly reaching a scale in some regions by the end of the century that has rarely, if ever, been observed in modern times.

Using an ensemble of 22 computer climate models and a comprehensive index of drought conditions, as well as analyses of previously published studies, the paper finds most of the Western Hemisphere, along with large parts of Eurasia, Africa, and Australia, may be at threat of extreme drought this century.

In contrast, higher-latitude regions from Alaska to Scandinavia are likely to become more moist.

Dai cautioned that the findings are based on the best current projections of greenhouse gas emissions. What actually happens in coming decades will depend on many factors, including actual future emissions of greenhouse gases as well as natural climate cycles such as El Niño.

The new findings appear this week as part of a longer review article in Wiley Interdisciplinary Reviews: Climate Change. The study was supported by the National Science Foundation, NCAR’s sponsor.

“We are facing the possibility of widespread drought in the coming decades, but this has yet to be fully recognized by both the public and the climate change research community,” Dai says. “If the projections in this study come even close to being realized, the consequences for society worldwide will be enormous.”

While regional climate projections are less certain than those for the globe as a whole, Dai’s study indicates that most of the western two-thirds of the United States will be significantly drier by the 2030s. Large parts of the nation may face an increasing risk of extreme drought during the century.

Other countries and continents that could face significant drying include:

* Much of Latin America, including large sections of Mexico and Brazil
* Regions bordering the Mediterranean Sea, which could become especially dry
* Large parts of Southwest Asia
* Most of Africa and Australia, with particularly dry conditions in regions of Africa
* Southeast Asia, including parts of China and neighboring countries

The study also finds that drought risk can be expected to decrease this century across much of Northern Europe, Russia, Canada, and Alaska, as well as some areas in the Southern Hemisphere. However, the globe’s land areas should be drier overall.

“The increased wetness over the northern, sparsely populated high latitudes can't match the drying over the more densely populated temperate and tropical areas,” Dai says.

A climate change expert not associated with the study, Richard Seager of Columbia University’s Lamont Doherty Earth Observatory, adds:

“As Dai emphasizes here, vast swaths of the subtropics and the midlatitude continents face a future with drier soils and less surface water as a result of reducing rainfall and increasing evaporation driven by a warming atmosphere. The term 'global warming' does not do justice to the climatic changes the world will experience in coming decades. Some of the worst disruptions we face will involve water, not just temperature.”

(Photo: UCAR)

UCAR

USING DISCARDS, SCIENTISTS DISCOVER DIFFERENT DINOSAURS STOMPING GROUNDS

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By examining the type of rock in which dinosaur fossils were embedded, an often unappreciated part of the remains, scientists have determined that different species of North American dinosaurs from the Late Cretaceous period 65 million years ago occupied different environments separated by just a few miles.

Hadrosaurs or duck-billed dinosaurs, along with the small ornithopod Thescelosaurus, preferred to live along the edge of rivers, according to the research. Ceratopsians, on the other hand, which include the well-known Triceratops, preferred to be several miles inland.

The findings, which appear in the online edition of the Proceedings of the Royal Society B, give scientists a more complete picture of the distribution of different species and help explain how several large herbivores managed to coexist.

Tyler Lyson of Yale University and the Marmarth Research Foundation, along with Yale researcher Nicholas Longrich, analyzed more than 300 fossils representing more than half a dozen dinosaur species from Western Canada, Montana, Wyoming and surrounding areas.

After several years of fieldwork, Lyson began to notice a pattern to the geographical distribution of different species. He and Longrich also searched through museum collections of fossils, some of which contained information about the type of rock in which the fossils were found, and some of which still had pieces of rock attached to them that were large enough for the researchers to recognize as either sandstone or mudstone.

“We’re using what paleontologists usually throw away when excavating the fossils as clues to where these different species spent most of their time,” Lyson said.

As the sole large carnivore in the region, Tyrannosaurs rex appears to have roamed both habitats, most likely feeding on large herbivores. However, the team discovered that hadrosaurs and Thescelosaurus fossils were more often found in sandstone, which occurs along riverbanks, whereas ceratopsians were likely to be embedded in mudstone from the floodplains.

“We didn’t really think about distribution between different species before now,” Longrich said. “But depending on what type of rock you look at, you get a very different picture of the community that lived there.”

The study also shows that the dinosaurs had specialized eating habits (something about which very little is known), and likely fed on different types of plants found in each environment, Longrich said.

“This opens up the possibility of finding new species if we search different types of rock,” Longrich said. “It also emphasizes the importance of recording data about the rock in which fossils are preserved, which can give us important clues as to the paleoecology of these animals.”

(Photo: Nicholas Longrich)

Yale University

NEED A STUDY BREAK TO REFRESH? MAYBE NOT, SAY STANFORD RESEARCHERS

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The researchers’ findings challenge the long-held theory that willpower is a limited resource that needs to be replenished.

It could happen to students cramming for exams, people working long hours or just about anyone burning the candle at both ends: Something tells you to take a break. Watch some TV. Have a candy bar. Goof off, tune out for a bit and come back to the task at hand when you’re feeling better. After all, you’re physically exhausted.

But a new study from Stanford psychologists suggests the urge to refresh (or just procrastinate) is – well – all in your head.

In a paper published in Psychological Science, the researchers challenge a long-held theory that willpower – defined as the ability to resist temptation and stay focused on a demanding task – is a limited resource. Scientists have argued that when willpower is drained, the only way to restore it is by recharging our bodies with rest, food or some other physical distraction that takes you away from whatever is burning you out.

Not so, says the Stanford team. Instead, they’ve found that a person’s mindset and personal beliefs about willpower determine how long and how well they’ll be able to work on a tough mental exercise.

“If you think of willpower as something that’s biologically limited, you’re more likely to be tired when you perform a difficult task,” said Veronika Job, the paper’s lead author. “But if you think of willpower as something that is not easily depleted, you can go on and on.”

Job, who conducted her research at Stanford and is now a postdoctoral scholar at the University of Zurich, co-authored the paper with Stanford psychology Professor Carol Dweck and Assistant Professor Greg Walton.

The researchers designed a series of four experiments to test and manipulate Stanford students’ beliefs about willpower. After a tiring task, those who believed or were led to believe that willpower is a limited resource performed worse on standard concentration tests than those who thought of willpower as something they had more control over.

They also found that leading up to final exam week, students who bought into the limited resource theory ate junk food 24 percent more often than those who believed they had more control in resisting temptation. The limited resource believers also procrastinated 35 percent more than the other group.

“The theory that willpower is a limited resource is interesting, but it has had unintended consequences,” Dweck said. “Students who may already have trouble studying are being told that their powers of concentration are limited and they need to take frequent breaks. But a belief in willpower as a non-limited resource makes people stronger in their ability to work through challenges.”

The Stanford researchers say their findings could help people who are battling distraction or temptation: diabetics following strict diets, people trying to overcome addictions, employees facing a tight deadline.

“This is an example of a context where people’s theories are driving outcomes,” Walton said. “Willpower isn’t driven by a biologically based process as much as we used to think. The belief in it is what influences your behavior.”

Association for Psychological Science

YOUNG CHILDREN ARE ESPECIALLY TRUSTING OF THINGS THEY’RE TOLD

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Little kids believe the darnedest things. For example, that a fat man in a red suit flies through the air on a sleigh pulled by reindeer. A new study on three-year-olds, published in Psychological Science, a journal of the Association for Psychological Science, finds that they aren’t just generally trusting. They’re particularly trusting of things people say to them.

Previous research has found that three-year-olds are a credulous bunch; they believe most things they’re told, and skepticism doesn’t kick in until later. Vikram K. Jaswal, of the University of Virginia, wanted to look more closely at trust in three-year-olds. Through his work on how young children learn language, he became interested in what they do with what they hear. “Why are they so willing to accept somebody else’s word, for example, that an eel is a fish, when it looks so much like a snake?” he asks. For this study, he and his students, A. Carrington Croft, Alison R. Setia, and Caitlin A. Cole, asked whether three-year-olds are more trusting of information they are told than the same information conveyed to them without words.

In one experiment, an adult showed children a red and a yellow cup, then hid a sticker under the red one. With some children, she claimed (incorrectly) that the sticker was under the yellow cup; with other children, she placed an arrow on the yellow cup without saying anything. The children were given the chance to search under one of the cups and allowed to keep the sticker if they found it. This game was repeated eight times (with pairs of differently colored cups).

The children who saw the adult put the arrow on the incorrect cup quickly figured out that they shouldn’t believe her. But the kids who heard the adult say the sticker was under a particular cup continued to take her word for where it was. Of those 16 children, nine never once found the sticker. Even when the adult had already misled them seven times in a row, on the eighth chance, they still looked under the cup where she said the sticker was. (At the end of the study, the children were given all the stickers whether or not they’d found any of them.)

“Children have developed a specific bias to believe what they’re told,” says Jaswal. “It’s sort of a short cut to keep them from having to evaluate what people say. It’s useful because most of the time parents and caregivers tell children things that they believe to be true.” Of course, there are times when people do lie to children—about Santa Claus, for example, but also in less innocuous situations. Jaswal says it is useful to understand the specifics of children’s trusting natures—in this case, to understand that they believe what people tell them, but can be more skeptical about information delivered in other ways.

Association for Psychological Science

PHOTOVOLTAIC MEDICINE

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Micro-scaled photovoltaic devices may one day be used to deliver chemotherapeutic drugs directly to tumors, rendering chemotherapy less toxic to surrounding tissue.

"In the first step, we were able to prove the concept," says Tao Xu, Ph.D., an assistant professor at the University of Texas in El Paso. Xu and his colleagues presented their findings at the AVS 57th International Symposium & Exhibition.

Currently, chemotherapeutic drugs are piped through an IV drip into the bloodstream, where they travel and come in contact with many organs on the way to their target. Patients are affected systemically, with toxic side effects that are well known. Ideally, clinicians would like to have a way to deliver these powerful drugs only where needed – to target them specifically to tumor tissue. Xu's device is designed to do just that - release drug only when stimulated by light, focusing it directly on a tumor during treatment. Near infrared or laser light is believed to penetrate tissues over 10 cm deep.

The novel device converts light into electric current. In an in vitro model system, positively or negatively charged "model" drugs were used to coated opposite sides of the miniature solar cell. Upon introduction of a light beam, one side of the device became positively charged, repelling the positive charged molecules the investigators had placed there, releasing them; the same thing happened with the negatively charged side and negative model molecules.

It appears that "our hypothesis will work," says Xu, adding that the amount of drug released can also be controlled by varying the intensity of light. The first phase employed an in vitro model; according to Xu, the next step for the work would be its application in small animal models.

American Institute of Physics

OLD BEES' MEMORIES FADE, MIRROR THAT OF MAMMALS

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A study published Oct. 19 in the open access journal Public Library of Science (PLoS) ONE, shows that not just human memories fade. Scientists from Arizona State University and the Norwegian University of Life Sciences examined how aging impacts the ability of honeybees to find their way home.

While bees typically are impressive navigators, able to wend their way home through complex landscapes after visits to flowers far removed from their nests, the study reveals that aging impairs the bees’ ability to extinguish the memory of an unsuitable nest site even after the colony has settled in a new home.

“From previous studies, we knew that old bees are characterized by poor learning when trained to floral odors in the laboratory,” said Gro Amdam, associate professor in the School of Life Sciences in ASU’s College of Liberal Arts and Sciences. “So, we wanted to test whether aging also affects learning behavior that is important for a bee’s survival in the wild.”

A bee is very well-trained as a forager after three to four days of flight time, Amdam said. Whereas mature bees have piloted their way to and from the hive for five to 11 days and old bees have had more than two weeks of flight time.

To test how old bees adapt to a changed home location, researchers trained bees to a new nest box while their former nest was closed off. Groups composed of mature and old bees were given several days in which to learn the new home location and to extinguish the bees’ memory of their unusable former nest box.

The scientists then disassembled the bees’ new home and forced groups of mixed-age bees to choose between three alternative nest locations, including the former nest box. Old bees with symptoms of senescence preferentially oriented toward the former nest site, despite the experience that should have told them that it was unusable.

“Although many old bees fail in learning tasks, we also discovered that a few still perform with excellence,” said Daniel Münch, lead author of the study and a senior life sciences researcher in Norway.

The scientists believe that their findings with bees offer a new means to model and understand the variability found in brain function between individuals, as some individuals’ memories remain intact while others’ learning behavior becomes inflexible with age.

(Photo: ASU)

Arizona State University

WHY THE LEOPARD GOT ITS SPOTS

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Why do leopards have rosette shaped markings but tigers have stripes? Rudyard Kipling suggested that it was because the leopard moved to an environment “full of trees and bushes and stripy, speckly, patchy-blatchy shadows” but is there any truth in this just-so story?

Researchers at the University of Bristol investigated the flank markings of 35 species of wild cats to understand what drives the evolution of such beautiful and intriguing variation. They captured detailed differences in the visual appearance of the cats by linking them to a mathematical model of pattern development.

They found that cats living in dense habitats, in the trees, and active at low light levels, are the most likely to be patterned, especially with particularly irregular or complex patterns. This suggests that detailed aspects of patterning evolve for camouflage. Analysis of the evolutionary history of the patterns shows they can evolve and disappear relatively quickly.

The research also explains why, for example, black leopards are common but black cheetahs unknown. Unlike cheetahs, leopards live in a wide range of habitats and have varied behavioural patterns. Having several environmental niches that different individuals of the species can exploit allows atypical colours and patterns to become stable within a population.

Although a clear link between environment and patterning was established, the study also highlighted some anomalies. For example, cheetahs have evolved or retained spotted patterns despite a strong preference for open habitats, while a number of cats, such as the bay cat and the flat-headed cat, have plain coats despite a preference for closed environments. Why this should be remains unclear.

The study also highlighted just how few species of cats have vertical stripes. Of the 35 species examined, only tigers always had vertically elongated patterns and these patterns were not associated with a grassland habitat, as might be expected. However, tigers seem to be very well camouflaged so this raises the question why vertical stripes are not more common in cats and other mammals.

Will Allen of Bristol’s School of Experimental Psychology, who led the research, said: “The method we have developed offers insights into cat patterning at many levels of explanation and we are now applying it to other groups of animals.”

(Photo: © Cai Priestley)

University of Bristol

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