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Nature press release for 10 May issue

May 10, 2001

[411163] SPACE: STAR EATS PLANET (pp163–166)
Astronomers finally have evidence that the Sun-like stars of extrasolar planetary systems are guilty of swallowing the planets in orbit around them.
Garik Israelian at the Astrophysics Institute of the Canary Islands and colleagues have caught a planet-swallowing star (HD82943) redhanded with lithium-6 in its atmosphere. 6Li is rapidly burnt up early in the life of stars, but remains intact in planets, so the only way its presence in a Sun-like star can be explained is if the star swallowed one or more of its planets whole. That the star HD82943 also has two planets around it — one in a highly eccentric orbit — adds weight to the idea that at least one of its original planets was swallowed.
The recently discovered extrasolar planetary systems have puzzled astronomers because many of the planets seem too close to their stars to have formed there. One way to get them there is to have multiple planets in a system interacting in a kind of gravitational billiards game, in which one is flung in towards the star — sometimes to be swallowed whole — while another goes into an eccentric orbit, or may even be ejected altogether.
CONTACT:
Garik Israelian (available from 7 May) tel +34 922 605258, e-mail gil@ll.iac.es

[411189] BRAIN: SIZE MATTERS (pp189–193; 193–195; N&V)
Humans are proud of their big brains. But humans are big animals — so are our brains anything special? Yes, say researchers who have studied the relative size of different brain regions across a wide range of mammal species. They also describe general trends in brain evolution across a range of mammal species.
Samuel Wang, of Princeton University, and colleagues compared the relative sizes of different brain areas — they worked out what percentage of the total brain volume was accounted for by the cortex, the cerebellum and so on. They found that, within a mammalian group such as insectivores or primates, the relative sizes of different bits of the brain remained fairly constant, despite huge variations in brain size. Between groups, however, there were big differences in brain architecture. Wang and colleagues have named their measure of brain structure the ‘cerebrotype’.
A change in cerebrotype often accompanies the emergence of new groups. Within the primates, for example, the passage from the older lemurs through to more recent monkeys and then apes and hominids is mirrored by progressive enlargement of the neocortex relative to the other brain regions. The researchers propose that this change is an evolutionary adaptation for living in larger groups and having a more complex social life.
Another paper this week looks at the cellular relations that might give rise to the disproportionately large cortex of the human brain. Charles Stevens, of the Salk Institute, La Jolla, California, looked at two regions of the cortex involved in processing visual information: the lateral geniculate nucleus (LGN), which is one of the first destinations for impulses from the retina, and the primary visual cortex, the destination for messages from the LGN.
Across primate species, Stevens found that the number of cells in primary visual cortex is proportional to the number of cells in the LGN raised to the power of 3/2. This means that a human uses four times as many neurons to process the input from each LGN neuron as a tarsier. He suggests that this relationship follows from the need for more neurons to process the greater amount of information collected by larger eyes at an optimal level of resolution.
In an accompanying News and Views article, Jon H. Kaas and Christine E. Collins of Vanderbilt University, Nashville, Tennessee, discuss the ramifications of these papers and a related pair recently published in Science.
CONTACT:
Samuel Wang tel +1 609 258 0388, e-mail samwang@molbio.princeton.edu
Charles Stevens tel +1 858 453 4100 ext 1155, e-mail stevens@salk.edu
Jon H. Kaas tel +1 615 322 6029, e-mail jon.h.kaas@vanderbilt.edu

[411156] ECOLOGY: THE PRIVATE LIFE OF COD (p156)
Cod now move in a less mysterious way, thanks to the efforts of David Righton, of the Centre for Environment, Fisheries and Aquaculture Science in Lowestoft, UK, and colleagues. Using electronic data-storage tags, they were able to plot the to-ings and fro-ings of cod in the North and Irish Seas. The differences between the two populations were surprising.
In a Brief Communication, they describe how cod in the Irish Sea are active at all times of the day and year, but those in the North Sea spend the summer months on the seabed, and move little. This finding could have significant implications for the management of the imperilled cod stocks of these regions, based as it is on closing particular areas of the sea to fishing.
CONTACT:
David Righton tel +44 1502 524 359, e-mail d.righton@cefas.co.uk

[411180] EARTH: STRESS HASTENS FAULT FAILURE (pp180–183; N&V)
The magnitude 7.1 Hector Mine earthquake may have been triggered by another, the magnitude 7.3 Landers earthquake that occurred only 20 kilometres away in southern California seven years earlier, suggest Andrew M. Freed of the Carnegie Institution of Washington DC and Jian Lin of the Woods Hole Oceanographic Institution, Massachusetts, in this week’s Nature.
       Freed and Lin show how continued deformation of the Earth’s crust after the Landers earthquake may have triggered the Hector Mine earthquake. Their modelling study shows that, within a few years of an earthquake, postseismic deformation may change stresses in the upper crust by at least as much as the stress released by the earthquake itself.
       “The study shows, too, that estimating such changes is crucial for characterizing regional seismic hazard,” comments Elizabeth Harding Hearn of the Massachusetts Institute of Technology, Cambridge, in an accompanying News and Views article.
CONTACT:
Andrew M. Freed tel +1 202 478 8827, e-mail freed@dtm.ciw.edu
Elizabeth Harding Hearn tel +1 617 253 3077, e-mail lizh@chandler.mit.edu

[411199] LIFELINES: THE MISSING LINK (pp199–204)
One approach to mapping disease genes and tracing population history involves resolving the human chromosomes into underlying ‘ancestral segments’ — regions that have been passed down through the generations largely intact from the founders of a population. Evidence for the ancestral segments is measured as ‘linkage disequilibrium’ among variants along the chromosome, and this parameter is also used to detect the presence of variants near or in disease genes.
This week Eric S. Lander of the Whitehead Institute/MIT Center for Genome Research, Cambridge, Massachusetts, and colleagues present the first large-scale investigation of linkage disequilibrium. They have determined the linkage of 19 genomic regions in populations of European Americans and Africans. The results are revealing in terms of both disease mapping and population history. The data point to a demographic bottleneck in northern Europe between 30,000 and 50,000 years ago, perhaps a relic of depopulation in the ice age, or a recent ‘out of Africa’ scenario.
CONTACT:
Eric Lander tel +1 617 258 5192, e-mail lander@genome.wi.mit.edu

[411157] CLIMATE: EAST DRIED AFRICA (pp157–162; N&V)
Tectonic changes in the Indonesian region, rather than North Atlantic glaciation, may have been responsible for the drying out of the African climate that is thought to have influenced early human evolution three million years ago. So suggest Mark Cane of Lamont Doherty Earth Observatory, Columbia University, Palisades, and Peter Molnar of the Massachusetts Institute of Technology, Cambridge, in this week’s Nature.
Analysing the northward migration of the Australian plate, the researchers reconstruct the position of the main ocean gateway between the Pacific and Indian Oceans. The northward shift of the entrance to the Indian Ocean could have caused colder north Pacific waters to enter the Indian Ocean around three million years ago, rather than warmer southern Pacific water masses as before. This would have reduced evaporation from the Indian Ocean and caused a more arid climate in Africa.
The researchers go on to suggest that the onset of glacial–interglacial cycles at around that time might have been triggered by the consequent changes in the distribution of water masses in the Pacific Ocean.
James D. Wright of Rutgers University, Piscataway, New Jersey, discusses the background and implications of this work in an accompanying News and Views article.
CONTACT:
Mark Cane tel +1 845 365 8344, e-mail mcane@ldeo.columbia.edu
James Wright tel +1 732 445 5722, e-mail jdwright@email.rci.rutgers.edu

[411154] LIFELINES: LEAVING WISDOM FOR FUTURE GENERATIONS (p154)
Old leaves pass their wisdom down to their juniors. In a Brief Communication, researchers at the University of Sheffield, UK, show that mature leaves of Arabidopsis thaliana pass on information about the level of light and carbon dioxide in their environment to developing leaves on the same plant. The youngsters then adjust the number of their stomata — the pores in the leaves that are crucial for photosynthesis and water balance — accordingly.
By placing mature and growing leaves in different levels of carbon dioxide and light, F I Woodward and colleagues showed that the make-up of the young leaf matched the environment of the older leaves rather than its own. The researchers suggest that this response may be a globally significant, and as yet unconsidered, aspect of the way that plant communities will adapt to higher atmospheric carbon dioxide.
CONTACT:
Ian Woodward tel +44 114 222 4647, e-mail f.i.woodward@sheffield.ac.uk

[411186] LIFELINES: ACCOUNTING FOR TASTE (pp186–189)
Once a tobacco hornworm larva has tasted potato, nothing else will do. Potato-reared larvae will actually starve to death rather than eat another type of plant, Marta del Campo of Cornell University, Ithaca, New York, and Binghamton University, New York, and colleagues report in this week’s Nature. Larvae brought up on plants not of the family Solanaceae will tuck into any old foliage.
       This taste-tuning seems to result from a compound present in solanaceous plants called Indioside D. Having been exposed to Indioside D, sensory neurons on the mouth parts of the larvae react differently to other plant compounds and lead the larvae to reject all but foliage containing Indioside D.
CONTACT:
Marta del Campo tel +1 607 254 6743, e-mail moliva@binghamton.edu

[411183] CLIMATE: PENGUINS FEEL THE HEAT (pp183–186)
Emperor penguins seem to be feeling the heat. Over the past 50 years — during which there was an abnormally warm spell in the Southern Ocean — the population of Antarctic emperor penguins has declined by 50%, report Christophe Barbraud and Henri Wirmerskirch of the Centre d’Etudes Biologiques de Chize, CNRS, Villiers en Bois, France, in this week’s Nature.
       “Our results indicate that emperor penguins may be very susceptible to environmental variability,” the team says. They used the longest time series available of demographic parameters of an Antarctic large predator breeding on fast ice and relying on food resources from the Southern Ocean. They found that penguin mortality rates increased when warm sea-surface temperatures occurred in the birds’ foraging area and when annual sea-ice extent was reduced.
CONTACT:
Christophe Barbraud (currently at Tour du Valat, Arles) tel +33 4 90 97 20 13, e-mail barbraud@tour-du-valat.com
Henri Weimerskirch tel +33 5 49 09 78 15, e-mail henriw@cebc.cnrs.fr

[411153] …AND FINALLY: LOBSTERS MAKE VILE DIN (pp153-154)
When attacked by predators, spiny lobsters (Palinuridae) startle their assailant by emitting a strident rasping noise. It may come as a surprise that, to make this offputting racket, the crustacean uses the same principles as the violin.
Sheila Patek of Duke University, Durham, North Carolina, found that the lobster has a soft ‘plectrum’ on its antenna, and a plate covered in microscopic ridges, like a file, just below its eye. In a Brief Communication, she describes how, when the lobster scrapes its antenna over the file, the plectrum sticks and slips many times — as does a violin bow passing over a string — and an alarming rasping sound results.
The lobsters’ reliance on soft parts to produce this warning sound allows them to make it even just after moulting, before their exoskeletons have had a chance to harden up, when they are most vulnerable to attack. This mechanism contrasts with the one used by crickets, which make their chirps by rubbing a hard plectrum over large ridges in a fashion more akin to strumming a washboard.
CONTACT:
Sheila Patek tel +1 919 660 7265, e-mail snp2@duke.edu

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