[1] Animal welfare: The coop coup (pp342-344)
Stocking density undoubtedly affects chicken welfare, but it's not the only factor to do so, research in this week's Nature suggests. Environmental factors, such as humidity and air ammonia, may also affect chicken health.
Chickens are big business — every year, around 20 billion broiler chickens (reared for meat) end up on dinner tables around the world. But the industry also attracts accusations of poor animal welfare. Many believe that overcrowding causes ill health.
The study, carried out by Marian Stamp Dawkins and colleagues, covered 2.7 million birds from ten different major broiler producers — an unprecedented act of commercial cooperation. When chickens were housed at high densities, they jostled more and also grew more slowly than animals with more space. But stocking density differences were overshadowed by much larger differences in environmental variation between companies. Temperature, humidity, litter moisture and air ammonia also affected animal health, enabling some companies to cope with high stocking densities more effectively.
The research is timely as the European Union is currently adopting standards for stocking density. Legislation to limit overcrowding that does not consider the environment might have major repercussions for European poultry producers without the hoped-for improvements in animal welfare.
[2] Psychology: Sleep on it (pp352-355;N&V)
Good news for those who find it hard to prise themselves from their duvets — research in this week's Nature suggests that sleep may stimulate creative thinking.
Does the following sound familiar? The solution to a seemingly unfathomable problem, left unresolved in the evening, effortlessly pops into your head the following morning. The experience is common, yet anecdotal. Now Jan Born and colleagues have devised an experiment to see whether the phenomenon stands up to scientific scrutiny.
Subjects were taught two simple rules to help them convert a string of eight digits into a new order. Unbeknownst to them, there was a third hidden rule that could only be gleaned through insight and allowed subjects to improve their performance rapidly. After initial training, subjects were allowed to sleep or forced to stay awake. Sleep worked wonders — subjects allowed an 8-hour snooze were twice as likely to work out the third rule as those that stayed awake, they found.
"The role that sleep plays in human creativity will be a mystery for some time yet," say Pierre Maquet and Perrine Ruby in an accompanying News and Views article. The study gives us good reason to respect our periods of sleep — especially given the current trend to curtail them recklessly, they add.
[3] Genetics: The Y chromosome gets fruity (pp348-352)
The papaya plant has a Y chromosome, research in this week's Nature reveals. The discovery may shed light on how sex chromosomes arise.
Plants and animals have evolved various systems for determining sex. One involves morphologically distinct sex chromosomes. Human females, for example, have a pair of X chromosomes, whereas human males have one X and one male-determining Y chromosome. These sex chromosomes have evolved over several million years, the Y being reduced gradually to the small size it is today. Most flowering plants are hermaphrodites, and those that have evolved to have different sexed individuals have done so much more recently.
Ray Ming and colleagues have discovered that the papaya (Carica papaya) plant carries a primitive Y chromosome, 10% of which is involved in sex determination. This male-specific region has a lower gene density than the rest of the chromosome. It provides a glimpse of a sex chromosome newly formed from a 'regular' chromosome before evolution has set about whittling away all but its sex-determining genes.
[4] & [5] Health and Medicine: Waving feverishly (pp344-347 & 313-319; N&V)
Dengue fever epidemics in Thailand occur in a predictable three-year cycle, research in this week's Nature reveals. The discovery may aid the allocation of resources needed to contain future outbreaks.
Dengue fever is a mosquito-borne virus that infects 50 to 100 million people every year. Up to half a million of these infections occur as the severe, life-threatening form of the disease, dengue haemorrhagic fever (DHF). Donald S. Burke and colleagues collected information from 850,000 infections occurring in 72 provinces of Thailand between 1983 and 1997. The three-year cycle originates in Bangkok, they report. From there it spreads outwards at a speed of 148 kilometres per month.
A second paper, also published in this week's Nature, sheds light on how the dengue virus infects host cells. The virus is known to enter a host cell by fusing its membrane coat with that of the cell. Now Stephen C. Harrison and colleagues report the structure of a key protein involved in the procedure. The discovery reveals new aspects of the fusion process, and may aid strategies aimed at stopping viral entry into host cells. The issue is discussed further in an accompanying News and Views article by Theodore S. Jardetzky and Robert A. Lamb.
[6] Astronomy: Cosmic milestone revised (pp326-328; N&V)
Astronomers have refined their estimate of a classic cosmic milestone — the distance from Earth to the Pleiades star cluster, also known as the Seven Sisters. The measurement, which is used to help judge larger astronomical distances, may cast doubt on the reliability of data gathered from the European Hipparcos satellite.
Xiaopei Pan and colleagues studied the orbit of one of the stars in the Pleiades, and used this to estimate the distance of the whole star cluster to Earth. Their measurement agrees beautifully with other estimates based on the stars' colours and brightness, but contradicts the Hipparcos value, which is 10% smaller. Either our understanding of stars' life cycles is wrong, or Hipparcos is, they say.
In an accompanying News and Views article, Bohdan Paczynski says that if Hipparcos were right, it would also throw our estimates of the size of the Universe into doubt. "I think Pan has got it right," he says. "I would not be surprised if there turns out to be an unfortunate shift in the Hipparcos data. But if we are to have confidence in our measurements of astronomical distances, this problem must be solved."
[7] Animal psychology: Unsettled rats lack positive outlook (p312)
Rats living in unsettling conditions are less likely to anticipate a positive event such as feeding, according to a Brief Communication in this week's Nature. The discovery may help to guide improvements in animal welfare.
Michael Mendl and colleagues trained rats to press a lever to deliver food when they heard a certain tone. A different tone indicated that they should leave the lever alone to avoid receiving a nasty blast of noise. When training was complete, the authors played intermediate tones to the animals. Rats that had been exposed to 'unpredictable' conditions — in which the cage floor was tilted, bedding was damp, or an unfamiliar rat was present — that cause a mild depression-like state were less likely to press the lever in response to one of these ambiguous tones.
This shows that rats under such circumstances are more likely to interpret stimuli as 'bad', and may therefore have a lower expectation of positive events, the authors explain — an outlook shared by mildly depressed humans.
[8] Geochemistry: Carbon from combustion goes AWOL (pp336-339; N&V)
The amount of carbon from wildfires and fossil-fuel burning that ends up in ocean sediments has probably been overestimated, researchers report in this week's Nature. The findings cast doubt on the idea that most of the carbon from combustion is locked away at the bottom of the sea.
Much of the carbon in marine sediments comes instead from the weathering of rocks, report Angela F. Dickens and her colleagues. Sediment samples bore the radioactive-element signature of fossilized organic matter, they found.The discovery raises the question of what eventually happens to the carbon, says Michael Schmidt in an accompanying News and Views article. It may also force geochemists to rethink the assumptions that underlie carbon-dating techniques.
[9] Earth Science: Journey to the centre of the Earth (pp339-342)
Scientists have recreated conditions as extreme as those found at the Earth's core to work out how the iron there behaves, according to research published in this week's Nature.
Because earth scientists can't learn about the core first hand, Ã la Jules Verne, their knowledge depends on measuring the seismic waves that move through the Earth's guts. But they also need to know exactly how iron behaves under intense pressure to infer the temperature and exact structure of the core.
J. H. Nguyen and N. C. Holmes used a small diamond 'anvil', where they hammered a sample of iron with a gas gun capable of generating more than two million times the atmospheric pressure.
The authors claim their results show that the Earth's solid core starts to melt at a lower pressure than scientists previously thought. They also say that the core is probably made of only one form of densely compacted iron, rather than two different forms, as earth scientists have assumed for the past 20 years.
[10] And Finally"¦: Juggling students have skill on the brain (pp311-312)
Learning to juggle can temporarily change the structure of your brain, researchers report in a Brief Communication in this week's Nature. The discovery challenges the traditional view that brain anatomy does not change in response to new stimuli.
Arne May and colleagues gave subjects the task of training themselves to juggle three balls for 60 seconds. After three months, brain scans of the juggling students showed an increase in the amount of grey matter — which consists largely of the cell bodies of neurons — in regions involved in the processing of visual motion information. Students who had not undergone juggling training showed no such change.
After a further three months, during which subjects did not juggle at all, the increases had partly subsided, showing the temporary nature of the anatomical alterations. The changes may be due to an increase in cell production or to changes in the connections between cells, the authors speculate.
ALSO IN THIS ISSUE"¦
[11] Conformational change and protein"protein interactions of the fusion protein of Semliki Forest virus (pp320-325)
[12] The microscopic nature of localization in the quantum Hall effect (pp328-332)
[13] Lymphocyte egress from thymus and peripheral lymphoid organs is dependent on S1P receptor (pp355-360)
[14] The mitochondrial calcium uniporter is a highly selective ion channel (pp360-364)
[15] The MAPK Hog1 recruits Rpd3 histone deacetylase to activate osmoresponsive genes (pp370-374)
GEOGRAPHICAL LISTING OF AUTHORS"¦
The following list of places refers to the whereabouts of authors on the papers numbered in this release. For example, London: 4 - this means that on paper number four, there will be at least one author affiliated to an institute or company in London. The listing may be for an author's main affiliation, or for a place where they are working temporarily. Please see the PDF of the paper for full details.
FRANCEGif-sur-Yvette: 11Marseilles: 11
GERMANYCologne: 2Jena: 10Luebeck: 2Regensburg: 10Stuttgart: 12
ISRAELRehevot: 12
SPAINBarcelona: 15Valencia: 15
SWITZERLANDBasel: 13
THAILANDBangkok: 4Nonthaburi: 4
UNITED KINGDOMLangford: 7London: 1Oxford: 1
UNITED STATES OF AMERICACalifornia Livermore: 9 Pasadena: 6, 8 San Francisco: 13 Santa Barbara: 8Georgia Athens: 3 Savannah: 8Hawaii Aiea: 3, 5 Hilo: 3 Honolulu: 3 Waialua: 3Maryland Baltimore: 4 Bethesda: 13 Fort Detrick: 4 Greenbelt: 4Massachusetts Boston: 5, 14New York Bronx: 11 Ithaca: 12Washington Seattle: 8
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