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2013年6月4日星期二

Solar system's Milky Way neighborhood gets more respect

"Our new evidence suggests that the Local Arm should appear as a prominent feature of the Milky Way," said Alberto Sanna, of the Max-Planck Institute for Radio Astronomy. Sanna and his colleagues presented their findings to the American Astronomical Society's meeting in Indianapolis, Indiana.

Determining the structure of our own Galaxy has been a longstanding problem for astronomers because we are inside it. In order to map the Milky Way, scientists need to accurately measure the distances to objects within the Galaxy. Measuring cosmic distances, however, also has been a difficult task, leading to large uncertainties. The result is that, while astronomers agree that our Galaxy has a spiral structure, there are disagreements on how many arms it has and on their specific locations.

To help resolve this problem, researchers turned to the VLBA and its ability to make the most accurate measurements of positions in the sky available to astronomers. The VLBA's capabilities allowed the astronomers to use a technique that yields accurate distance measurements unambiguously through simple trigonometry.

By observing objects when Earth is on opposite sides of its orbit around the Sun, astronomers can measure the subtle shift in the object's apparent position in the sky, compared to the background of more-distant objects. This effect is called parallax, and can be demonstrated by holding your finger close to your nose and alternately closing each eye.

The VLBA's ability to precisely measure very tiny shifts in apparent position allows scientists to use this trigonometric method to directly determine distances much farther from Earth than previously was possible.

The astronomers used this method to measure the distances to star-forming regions in the Milky Way where water and methanol molecules are boosting radio waves in the same fashion that a laser boosts light waves. These objects, called masers, are like lighthouses for the radio telescopes. The VLBA observations, carried out from 2008 to 2012, produced accurate distance measurements to the masers and also allowed the scientists to track their motion through space.

A striking result was an upgrade to the status of the Local Arm within which our Solar System resides. We are between two major spiral arms of the Galaxy, the Sagittarius Arm and the Perseus Arm. The Sagittarius Arm is closer to the Galactic center and the Perseus Arm is farther out in the Galaxy. The Local Arm previously was thought to be a minor structure, a "spur" between the two longer arms. Details of this finding were published in the Astrophysical Journal by Xu Ye and collaborators.

"Based on both the distances and the space motions we measured, our Local Arm is not a spur. It is a major structure, maybe a branch of the Perseus Arm, or possibly an independent arm segment," Sanna said.

The scientists also presented new details about the distribution of star formation in the Perseus Arm, and about the more-distant Outer Arm, which encompasses a warp in our Galaxy.

The new observations are part of an ongoing project called the Bar and Spiral Structure Legacy (BeSSeL) survey, a major effort to map the Milky Way using the VLBA. The acronym honors Friedrich Wilhelm Bessel, the German astronomer who made the first accurate measurement of a star's parallax in 1838.

The VLBA, dedicated in 1993, uses ten, 25-meter-diameter dish antennas distributed from Hawaii to St. Croix in the Caribbean. It is operated from the NRAO's Domenici Science Operations Center in Socorro, NM. All ten antennas work together as a single telescope with the greatest resolving power available to astronomy. This unique capability has produced landmark contributions to numerous scientific fields, ranging from Earth tectonics, climate research, and spacecraft navigation, to cosmology.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

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Vegetarian diets associated with lower risk of death

June 3, 2013 — Vegetarian diets are associated with reduced death rates in a study of more than 70,000 Seventh-day Adventists with more favorable results for men than women, according to a report published Online First by JAMA Internal Medicine, a JAMA Network publication.

The possible relationship between diet and mortality is an important area of study. Vegetarian diets have been associated with reductions in risk for several chronic diseases, including hypertension, metabolic syndrome, diabetes mellitus and ischemic heart disease (IHD), according to the study background.

Michael J. Orlich, M.D., of Loma Linda University in California, and colleagues examined all-cause and cause-specific mortality in a group of 73,308 men and women Seventh-day Adventists. Researchers assessed dietary patients using a questionnaire that categorized study participants into five groups: nonvegetarian, semi-vegetarian, pesco-vegetarian (includes seafood), lacto-ovo-vegetarian (includes dairy and egg products) and vegan (excludes all animal products).

The study notes that vegetarian groups tended to be older, more highly educated and more likely to be married, to drink less alcohol, to smoke less, to exercise more and to be thinner.

"Some evidence suggests vegetarian dietary patterns may be associated with reduced mortality, but the relationship is not well established," the study notes.

There were 2,570 deaths among the study participants during a mean (average) follow-up time of almost six years. The overall mortality rate was six deaths per 1,000 person years. The adjusted hazard ratio (HR) for all-cause mortality in all vegetarians combined vs. nonvegetarians was 0.88, or 12 percent lower, according to the study results. The association also appears to be better for men with significant reduction in cardiovascular disease mortality and IHD death in vegetarians vs. nonvegetarians. In women, there were no significant reductions in these categories of mortality, the results indicate.

"These results demonstrate an overall association of vegetarian dietary patterns with lower mortality compared with the nonvegetarian dietary pattern. They also demonstrate some associations with lower mortality of the pesco-vegetarian, vegan and lacto-ovo-vegetarian diets specifically compared with the nonvegetarian diet," the authors conclude.

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A grassy trend in human ancestors' diets

In four new studies of carbon isotopes in fossilized tooth enamel from scores of human ancestors and baboons in Africa from 4 million to 10,000 years ago, a team of two dozen researchers found a surprise increase in the consumption of grasses and sedges -- plants that resemble grasses and rushes but have stems and triangular cross sections.

"At last, we have a look at 4 million years of the dietary evolution of humans and their ancestors," says University of Utah geochemist Thure Cerling, principal author of two of the four new studies published online June 3 by the journal Proceedings of the National Academy of Sciences. Most funding was from the National Science Foundation.

"For a long time, primates stuck by the old restaurants -- leaves and fruits -- and by 3.5 million years ago, they started exploring new diet possibilities -- tropical grasses and sedges -- that grazing animals discovered a long time before, about 10 million years ago" when African savanna began expanding, Cerling says. "Tropical grasses provided a new set of restaurants. We see an increasing reliance on this new resource by human ancestors that most primates still don't use today."

Grassy savannas and grassy woodlands in East Africa were widespread by 6 million to 7 million years ago. It is a major question why human ancestors didn't seriously start exploiting savanna grasses until less than 4 million years ago.

The isotope method cannot distinguish what parts of grasses and sedges human ancestors ate -- leaves, stems, seeds and-or underground storage organs such as roots or rhizomes. The method also can't determine when human ancestors began getting much of their grass by eating grass-eating insects or meat from grazing animals. Direct evidence of human ancestors scavenging meat doesn't appear until 2.5 million years ago, and definitive evidence of hunting dates to only about 500,000 years ago.

With the new findings, "we know much better what they were eating, but mystery does remain," says Cerling, a distinguished professor of geology and geophysics, and biology. "We don't know exactly what they ate. We don't know if they were pure herbivores or carnivores, if they were eating fish [which leave a tooth signal that looks like grass-eating], if they were eating insects or if they were eating mixes of all of these."

Why Our Ancestor's Diets Matter

The earliest human ancestor to consume substantial amounts of grassy foods from dry, more open savannas "may signal a major and ecological and adaptive divergence from the last common ancestor we shared with African great apes, which occupy closed, wooded habitats," writes University of South Florida geologist Jonathan Wynn, chief author of one of the new studies and a former University of Utah master's student.

"Diet has long been implicated as a driving force in human evolution," says Matt Sponheimer, a University of Colorado, Boulder anthropologist, former University of Utah postdoctoral fellow and lead author of the fourth study.

He notes that changes in diet have been linked to both larger brain size and the advent of upright walking in human ancestors roughly 4 million years ago. Human brains were larger than those of other primates by the time our genus, Homo, evolved 2 million years ago. (Our species, Homo sapiens, arose 200,000 years ago.)

"If diet has anything to do with the evolution of larger brain size and intelligence, then we are considering a diet that is very different than we were thinking about 15 years ago," when it was believed human ancestors ate mostly leaves and fruits, Cerling says.

How the Studies Were Performed: You Are What You Eat

The new studies analyze carbon isotope results from 173 teeth from 11 species of hominins. Hominins are humans, their ancestors and extinct relatives that split from the other apes roughly 6 million years ago. Some of the analyses were done in previous research, but the new studies include new carbon-isotope results for 104 teeth from 91 individuals of eight hominin species. Those teeth are in African museums and were studied by two groups working at separate early human sites in East Africa.

Wynn wrote the study about teeth from Ethiopia's Awash Basin-Hadar area, where research is led by Arizona State University's William Kimbel. Cerling wrote the study about teeth from the Turkana Basin in Kenya, where the research team is led by Turkana Basin Institute paleoanthropologist Meave Leakey, Cerling and geologist Frank Brown, dean of mines and Earth sciences at the University of Utah. Cerling also wrote a study about baboon diets. Sponheimer wrote a fourth study, summarizing the other three.

The method of determining ancient creatures' diets from carbon isotope data is less than 20 years old and is based on the idea "you are what you eat," Sponheimer says.

Tiny amounts of tooth enamel were drilled from already broken fossil teeth of museum specimens of human ancestors and relatives. The powder was placed in a mass spectrometer to learn ratios of carbon isotopes incorporated into tooth enamel via diet.

The ratios of rare carbon-13 to common carbon-12 reveal whether an animal ate plants that used so-called C3, C4 or CAM photosynthesis to convert sunlight to energy. Animals eating C4 and CAM plants have enriched amounts of carbon-13.

C3 plants include trees, bushes and shrubs, and their leaves and fruits; most vegetables; cool-season grasses and grains such as timothy, alfalfa, wheat, oats, barley and rice; soybeans; non-grassy herbs and forbs.

C4 plants are warm-season or tropical grasses and sedges and their seeds, leaves or storage organs like roots and tubers. Well-known sedges include water chestnut, papyrus and sawgrass. C4 plants are common in African savannas and deserts. C4 grasses include Bermuda grass and sorghum. C4 grains include corn and millet.

CAM plants include tropical succulent plants such as cactus, salt bush and agave.

Today, North Americans eat about half C3 plants, including vegetables, fruits and grains such as wheat, oats, rye and barley, and about half C4, which largely comes from corn, sorghum and meat animals fed on C4 grasses and grains, Cerling says.

The highest human C3 diets today are found in northern Europe, where only C3 cool-season grasses grow, so meat animals there graze them, not C4 tropical grasses. The highest C4 diets likely are in Central America because of the heavily corn-based diet.

If early humans ate grass-eating insects or large grazing animals like zebras, wildebeest and buffalo, it also would appear they ate C4 grasses. If they ate fish that ate algae, it would give a false appearance of grass-eating because of the way algae takes up carbonate from water, Cerling says. If they ate small antelope and rhinos that browsed on C3 leaves, it would appear they ate C3 trees-shrubs. Small mammals such as hyrax, rabbits and rodents would have added C3 and C4 signals to the teeth of human ancestors.

The Findings: A Dietary History of Human Ancestors and Relatives

Previous research showed that 4.4 million years ago in Ethiopia, early human relative Ardipithecus ramidus ("Ardi") ate mostly C3 leaves and fruits.
About 4.2 million to 4 million years ago on the Kenyan side of the Turkana Basin, one of Cerling's new studies shows that human ancestor Australopithecus anamensis ate at least 90 percent leaves and fruits -- the same diet as modern chimps.
By 3.4 million years ago in northeast Ethiopia's Awash Basin, according to Wynn's study, Australopithecus afarensis was eating significant amounts of C4 grasses and sedges: 22 percent on average, but with a wide range among individuals of anywhere from 0 percent to 69 percent grasses and sedges. The species also ate some succulent plants. Wynn says that switch "documents a transformational stage in our ecological history." Many scientists previously believed A. afarensis had an ape-like C3 diet. It remains a mystery why A. afarensis expanded its menu to C4 grasses when its likely ancestor, A. anamensis, did not, although both inhabited savanna habitats, Wynn writes.
Also by 3.4 million years ago in Turkana, human relative Kenyanthropus platyops had switched to a highly varied diet of both C3 trees and shrubs and C4 grasses and sedges. The average was 40 percent grasses and sedges, but individuals varied widely, eating anywhere from 5 percent to 65 percent, Cerling says.
About 2.7 million to 2.1 million years ago in southern Africa, hominins Australopithecus africanus and Paranthropus robustus ate tree and shrub foods, but also ate grasses and sedges and perhaps grazing animals. A. africanus averaged 50 percent C4 grass-sedge-based foods, but individuals ranged from none to 80 percent. P. robustus averaged 30 percent grasses-sedges, but ranged from 20 percent to 50 percent.
By 2 million to 1.7 million years ago in Turkana, early humans, Homo, ate a 35 percent grass-and-sedge diet -- some possibly from meat of grazing animals -- while another hominin, Paranthropus boisei, was eating 75 percent grass -- more than any hominin, according to a 2011 study by Cerling. Paranthropus likely was vegetarian. Homo had a mixed diet that likely included meat or insects that had eaten grasses. Wynn says a drier climate may have made Homo and Paranthropus more reliant on C4 grasses.
By 1.4 million years ago in Turkana, Homo had increased the proportion of grass-based food to 55 percent.
Some 10,000 years ago in Turkana, Homo sapiens' teeth reveal a diet split 50-50 between C3 trees and shrubs and C4 plants and likely meat -- almost identical to the ratio in modern North Americans, Cerling says.

Humans: The Only Surviving Primates with a C4 Grass Diet

Cerling's second new study shows that while human ancestors ate more grasses and other apes stuck with trees and shrubs, two extinct Kenyan baboons represent the only primate genus that ate primarily grasses and perhaps sedges throughout its history.

Theropithecus brumpti ate a 65 percent tropical grass-and-sedge diet when the baboons lived between 4 million and 2.5 million years ago, contradicting previous claims that they ate forest foods. Later, Theropithecus oswaldi ate a 75 percent grass diet by 2 million years ago and a 100 percent grass diet by 1 million years ago. Both species went extinct, perhaps due to competition from hooved grazing animals. Modern Theropithecus gelada baboons live in Ethiopia's highlands, where they eat only C3 cool-season grasses.

Cerling notes that primate tropical grass-eaters -- Theropithecus baboons and Paranthropus human relatives -- went extinct while human ancestors ate an increasingly grass-based diet. Why is an open question.

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Solar system's Milky Way neighborhood gets more respect

The scientists also presented new details about the distribution of star formation in the Perseus Arm, and about the more-distant Outer Arm, which encompasses a warp in our Galaxy.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

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Vegetarian diets associated with lower risk of death

The study notes that vegetarian groups tended to be older, more highly educated and more likely to be married, to drink less alcohol, to smoke less, to exercise more and to be thinner.

"Some evidence suggests vegetarian dietary patterns may be associated with reduced mortality, but the relationship is not well established," the study notes.

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A grassy trend in human ancestors' diets

Why Our Ancestor's Diets Matter

How the Studies Were Performed: You Are What You Eat

The method of determining ancient creatures' diets from carbon isotope data is less than 20 years old and is based on the idea "you are what you eat," Sponheimer says.

CAM plants include tropical succulent plants such as cactus, salt bush and agave.

The Findings: A Dietary History of Human Ancestors and Relatives

Previous research showed that 4.4 million years ago in Ethiopia, early human relative Ardipithecus ramidus ("Ardi") ate mostly C3 leaves and fruits.
About 4.2 million to 4 million years ago on the Kenyan side of the Turkana Basin, one of Cerling's new studies shows that human ancestor Australopithecus anamensis ate at least 90 percent leaves and fruits -- the same diet as modern chimps.
By 3.4 million years ago in northeast Ethiopia's Awash Basin, according to Wynn's study, Australopithecus afarensis was eating significant amounts of C4 grasses and sedges: 22 percent on average, but with a wide range among individuals of anywhere from 0 percent to 69 percent grasses and sedges. The species also ate some succulent plants. Wynn says that switch "documents a transformational stage in our ecological history." Many scientists previously believed A. afarensis had an ape-like C3 diet. It remains a mystery why A. afarensis expanded its menu to C4 grasses when its likely ancestor, A. anamensis, did not, although both inhabited savanna habitats, Wynn writes.
Also by 3.4 million years ago in Turkana, human relative Kenyanthropus platyops had switched to a highly varied diet of both C3 trees and shrubs and C4 grasses and sedges. The average was 40 percent grasses and sedges, but individuals varied widely, eating anywhere from 5 percent to 65 percent, Cerling says.
About 2.7 million to 2.1 million years ago in southern Africa, hominins Australopithecus africanus and Paranthropus robustus ate tree and shrub foods, but also ate grasses and sedges and perhaps grazing animals. A. africanus averaged 50 percent C4 grass-sedge-based foods, but individuals ranged from none to 80 percent. P. robustus averaged 30 percent grasses-sedges, but ranged from 20 percent to 50 percent.
By 2 million to 1.7 million years ago in Turkana, early humans, Homo, ate a 35 percent grass-and-sedge diet -- some possibly from meat of grazing animals -- while another hominin, Paranthropus boisei, was eating 75 percent grass -- more than any hominin, according to a 2011 study by Cerling. Paranthropus likely was vegetarian. Homo had a mixed diet that likely included meat or insects that had eaten grasses. Wynn says a drier climate may have made Homo and Paranthropus more reliant on C4 grasses.
By 1.4 million years ago in Turkana, Homo had increased the proportion of grass-based food to 55 percent.
Some 10,000 years ago in Turkana, Homo sapiens' teeth reveal a diet split 50-50 between C3 trees and shrubs and C4 plants and likely meat -- almost identical to the ratio in modern North Americans, Cerling says.

Humans: The Only Surviving Primates with a C4 Grass Diet

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No early birds getting the worms: Songbirds risk missing peak food supply

June 3, 2013 — A mismatch between the departure schedules of songbirds and higher spring temperatures at their breeding sites is putting them at risk, according to a new study out of York University.

The study, "A Trans-Hemispheric Migratory Songbird Does Not Advance Spring Schedules or Increase Migration Rate in Response to Record-Setting Temperatures at Breeding Sites," published in the journal PLOS ONE, tracked the spring migration of purple martins over five years from the Amazon basin to two breeding sites in eastern North America. Researchers outfitted the birds with tiny geolocator "backpacks" to record data on their movements and found that the birds' departure times between years were surprisingly consistent, despite variation in temperature at their final destination.

"We found that purple martins migrating between the Amazon Basin and North America did not adjust their migration timing even during the hottest spring on record in 2012," says study author Kevin Fraser, a Postdoctoral Fellow in York's Department of Biology, Faculty of Science. "This means that they arrived 'late' for the advanced spring, and likely missed out on peak food they need to be productive breeders."

Aerial insectivores, like purple martins and other swallows, are experiencing strong population declines, particularly species migrating longer distances and populations breeding further north. Scientists have shown in a European species that declines may be due to an inability to advance arrival schedules to match a warming climate. This study provides the first direct evidence of a discrepancy between higher spring temperatures at breeding sites and departure schedules of individual songbirds.

"Our results suggest that long-distance migrants may receive limited or conflicting environmental cues about conditions at the breeding grounds while still at overwintering sites or along migration routes," says Fraser. "Once en route, the birds received no temperature cues of the warm spring until they reached the US Gulf coast, at which point it was likely too late to get to breeding sites earlier." Fraser says such mistiming is an active area of new research, and with climate change may be an important contributing factor to migratory songbird declines.

"Some migratory songbirds may not have the flexibility they need to respond quickly to earlier springs and more variable weather with climate change, which could contribute to the strong population declines we see in many species. Identifying which species or populations may be at greatest risk will be very important for guiding effective conservation action."

He says the study suggests that migration timing and rate in purple martin is not highly sensitive to short-term variation in temperature and rainfall, and that multiple years of increasing spring temperatures may be required to shift the birds to an earlier breeding arrival time through natural selection for earlier departure from tropical overwintering sites.

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Chimpanzees have five universal personality dimensions

June 3, 2013 — While psychologists have long debated the core personality dimensions that define humanity, primate researchers have been working to uncover the defining personality traits for humankind's closest living relative, the chimpanzee. New research, published in the June 3 issue of American Journal of Primatology provides strong support for the universal existence of five personality dimensions in chimpanzees: reactivity/undependability, dominance, openness, extraversion and agreeableness with a possible sixth factor, methodical, needing further investigation.

"Understanding chimpanzee personality has important theoretical and practical implications," explained lead author Hani Freeman, postdoctoral fellow with the Lester E. Fisher Center for the Study and Conservation of Apes at Lincoln Park Zoo. "From an academic standpoint, the findings can inform investigations into the evolution of personality. From a practical standpoint, caretakers of chimpanzees living in zoos or elsewhere can now tailor individualized care based on each animal's personality thereby improving animal welfare."

The study of chimpanzee personality is not novel; however, according to the authors, previous instruments designed to measure personality left a number of vital questions unanswered.

"Some personality scales used for chimpanzees were originally designed for another species. These 'top-down' approaches are susceptible to including traits that are not relevant for chimps, or fail to include all the relevant aspects of chimpanzee personality," explained Freeman. "Another tactic, called a 'bottom-up' approach, derives traits specifically for chimpanzees without taking into account information from previous scales. This approach also has limitations as it impedes comparisons with findings in other studies and other species, which is essential if you want to use research on chimpanzees to better understand the evolution of human personality traits."

To address the limitations of each approach and gain a better understanding of chimpanzee personality, the authors developed a new personality rating scale that incorporated the strengths of both types of scales. This new scale consisted of 41 behavioral descriptors including boldness, jealousy, friendliness and stinginess amongst others. Seventeen raters who work closely and directly with chimpanzees used the scale to assess 99 chimpanzees in their care at the Michale E. Keeling Center for Comparative Medicine and Research, UT MD Anderson Cancer Center in Bastrop, Texas.

The chimpanzees rated were aged 8 to 48, a majority had been captive born and mother-raised, and all had lived at the facility for at least two years.

To validate their findings, the researchers used two years worth of behavioral data collected on the chimpanzees. As the authors expected, the findings showed the personality ratings were associated with differences in how the chimpanzees behaved. The researchers also showed the raters tended to agree in their independent judgments of chimpanzees' personalities, suggesting the raters were not merely projecting traits onto the chimpanzees.

Researchers suggest that one benefit to having the chimpanzees rated on the five core personality dimensions is that this information can now be used to make predictions that will help in their management, such as how individual chimpanzees will behave in various social situations. This type of information will help zoos better anticipate certain behaviors from various individuals, and will assist them in providing individualized care.

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