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Article Released Wed-19th-July-2006 21:53 GMT
Contact: Ruth Institution: Nature Publishing Group
 Top predators are crucial for binding ecosystems together

Summaries of newsworthy papers for Nature VOL.442 NO.7100 including Astrophysics: Nova again, Geology: How the Red Sea is parting again, Biology: Unexpected inheritance, Materials chemistry: Graphite unpeeled and finally... Pack it in!


This press release is copyright Nature.

This press release contains:

* Summaries of newsworthy papers:

Astrophysics: Nova again

Ecology: Top predators are crucial for binding ecosystems together

Geology: How the Red Sea is parting again

Biology: Unexpected inheritance

Materials chemistry: Graphite unpeeled

And finally... Pack it in!

* Mention of papers to be published at the same time with the same embargo
* Geographical listing of authors

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[1] & [2] Astrophysics: Nova again (pp 276-278; 279-281)

A rare glimpse into a cosmic explosion, known as a nova, is provided by two international teams of astronomers this week in Nature. They looked at X-rays and radio waves emitted from RS Ophiuchi, a 'variable star' almost 2,000 light years away that is prone to bright outbursts. RS Oph has been seen to 'erupt' six times since 1898, the last event being in February 2006. It is a member of the class of stars known as novae: small, compact white dwarfs in which occasional runaway nuclear reactions on their surface create the outbursts. Although the basic physical processes occurring in novae are well understood, no one has been too sure about how the eruptions happen, how much material is thrown off the surface of the star, or what happens to it.

The two teams of researchers deduce that RS Oph has a companion star, a massive red giant surrounded by a nebula of gas. During the outburst, material from the white dwarf smashes into the nebula, and the resulting explosion produces X-rays. The Rossi X-Ray Timing Explorer satellite detected these, and Jennifer Sokoloski and colleagues analyse the measurements to understand what the blast wave looked like over the several weeks during which it appeared and then faded.

They say that the wave of ejected material seems not to be a sphere, as would be expected if it was being blasted off everywhere on the white dwarf's surface. That conclusion is supported by observations of radio emission from RS Oph, also generated in the blast, by Tim O'Brien and his team. They monitored the shape of the shell of ejecta at radio frequencies for up to about seven weeks after the outburst, and find that it evolved into two lobes, suggesting - as has been suspected previously but not confirmed - that the nova outburst produces twin jets of stellar material that spew out in opposite directions. This in turn will help to clarify the process that triggers nova explosions.


Jennifer Sokoloski (Harvard-Smithsonian Center for Astrophysics Solar, Stellar, & Planetary Sciences, Cambridge, MA, USA) Author paper [1]
Tel: +1 617 496 7573; E-mail:

Tim O’Brien (Manchester University, UK) Author paper [2]
Tel: +44 1477 571321; E-mail:

[3] & [4] Ecology: Top predators are crucial for binding ecosystems together (pp 265-269; 259-264; N&V)

Complex ecosystems are held together by their top predators, according to a theoretical analysis published in this week’s Nature. Although food webs could not exist without the plants and microorganisms that form their basis, these complex tangles of relationships are crucially pinned together by the activities of their top carnivores. As these are the very species most under threat from humans, an international expert panel on biodiversity should be set up, argues a Commentary in the same issue.

Neil Rooney and his colleagues surveyed data from aquatic and terrestrial ecosystems across the world, including Chesapeake Bay off the eastern United States, the Alaskan tundra, a European pine forest, and even a Dutch experimental farm. They conclude that food webs consist of different “channels”, in which energy is passed upwards in the food chain at varying rates. These different rates are bound together by the activity of top predators, which feed from a range of different sources.

Ecological food webs are different to many other complex networks, Jose Montoya and colleagues point out in a Review article in the same issue. And this remarkable complexity means that conserving biodiversity may be an even greater challenge than tackling climate change, argue Michel Loreau, Alfred Oteng-Yeboah and co-authors in a related Commentary. They therefore call for the establishment of an international expert group, similar to the Intergovernmental Panel on Climate Change (IPCC), to address the problem.


Neil Rooney (University of Guelph, Canada) Author paper [3]
Tel: +1 519 824 4120 x56861; E-mail:

Jose Montoya (Queen Mary University London, UK) Author paper [4]
Please note that the author is in Spain and can be contacted on
Tel: +34 657 332 005/6; E-mail:

Michel Loreau (Universitite Pierre et Marie Curie, Paris, France) Commentary author
Tel: +1 44 32 37 09; E-mail:

Robert D Holt (University of Florida, Gainesville, FL, USA) N&V author
Tel: +1 352 392 691; E-mail:

[5] Geology: How the Red Sea is parting again (pp 291-294; N&V)

The largest single rip in the Earth’s continental crust during the era of satellite monitoring is described by Tim Wright and colleagues in Nature this week. Using the European Space Agency’s Envisat radar satellite, they looked at ground movements during the slow rupture of the Earth’s crust in the Afar depression in Ethiopia, in the southern end of the Red Sea.

Here the crust is being stretched and thinned as the Arabian tectonic plate moves away from the African (Nubian) plate, forming the Red Sea itself at the northern end of the Great Rift Valley. The observations may help to explain why such continental rifts are divided into segments.

The rifting process has been happening for the past 30 million years or so - but not smoothly. Occasionally the ripping of the crust takes place in lurches, accompanied by earthquakes and volcanic activity. One such event took place over several days in September 2005 in the Dabbahu volcanic massif of the Afar depression. This contains a 60-km-long segment of the rift, and the researchers found that this entire segment opened up during the episode.

As it did so, magma (molten rock) was drained from chambers lying beneath the Dabbahu and Gabho volcanoes at the northern end of the segment, filling up the gap left as the edges of the plates moved up to 8 metres apart. In all, about 2.5 cubic kilometres of magma entered the rift segment to form new continental crust. Wright and colleagues conclude that this process of magma intrusion into the gap, rather than cracking of the crust, is responsible for the segmentation of continental rifts.


Tim Wright (University of Oxford, UK)
Tel: +44 1865 272 068; E-mail:

Please note that the author is unavailable on Friday 14 July
Freysteinn Sigmundsson (University of Iceland, Reykjavik, Iceland) N&V author
Tel: +354 525 4494; E-mail:

[6] Biology: Unexpected inheritance (pp 295-298)

A paper in this week’s Nature adds weight to the emerging idea that RNA partly determines the inherited characteristics of plants and animals.

Vicki Chandler and her colleagues studied a phenomenon called paramutation: a form of non-mendelian inheritance in which one allele of a gene can heritably dampen the expression of another. They hunted down a gene called mop1 (mediator of paramutation1), which is required for paramutation at the b1 locus in maize, and found that it produces an enzyme that manufactures RNA.

The team proposes that this enzyme produces RNA from unique tandem repeats of DNA, which are also essential for paramutation at this locus. Although the details are not yet known, the repeat RNA may accumulate to a threshold level at which it establishes and maintains the heritable state of chromatin (DNA attached to proteins) required for silencing the maize b1 locus.

Vicki Chandler (University of Arizona, Tucson, AZ, USA)
Tel: +1 520 626 8725; E-mail:

[7] Materials chemistry: Graphite unpeeled (pp 282-286; N&V)

Graphene - sheets of graphite just one atom thick - has recently become one of the hottest materials around. Electrically conducting, it could provide the fabric for new kinds of microelectronic devices and circuits, but it is hard to make. Rodney Ruoff and colleagues show, in Nature this week, how to turn regular graphite into graphene sheets that are embedded in a polymer matrix, making a new electrically conducting composite material.

Graphite is a form of pure carbon made from stacks of flat sheets. Making isolated sheets - graphene - is not easy, however, because they tend to stick together. It has been long known that the sheets can be chemically modified by oxidation to form graphite oxide, in which oxygen-containing chemical groups are attached to some of the carbon atoms. Graphite oxide is thus rendered hydrophilic and can be separated into individual sheets merely by exposing it to ultrasound waves in water.

The team have found a way to turn graphite oxide into a graphene/polymer composite, by modifying it with a chemical so that, upon exposure to ultrasound, it will exfoliate in solvents that also dissolve polymers. This approach is the basis for the generation of polymer matrix composites containing graphene sheets. A reducing step introduced before polymer-graphene coagulation led to the formation of an electrically conducting material. Under an electron microscope, the final material resembles a block of ice full of pieces of crumpled paper.


Rodney Ruoff (Northwestern University, Evanston, IL, USA)
Please note that the author is in Greece and can be contacted up to 16 July on
Tel: +30 210 7706 611; E-mail:

From 17 July it may be easier to contact

Megan Fellman (Science Media Relations, Northwestern University, Evanston, IL, USA)
Tel: +1 847 491 3115; E-mail:

Nicholas A Kotov (University of Michigan, Ann Arbor, MI, USA) N&V Author
Tel: +1 734 763 8768; E-mail:

[8] And finally... Pack it in! (p 257)

The mechanics of packing grains, such as wheat in a silo or sand in a jar, are addressed in a Brief Communication in this week’s Nature. Peter Schiffer and colleagues show how an increase in grain packing can be induced by raising and then lowering the temperature of the stored material.

The packing fraction of a granular material is the fraction of the sample volume that is filled by grains rather than empty space. Shaking or tapping the container often helps to settle the contents, increasing this packing fraction, but that may not be an option for storage in industrial settings. As temperature changes are known to affect pressure in the contents of silos, the team examined the dynamics of this effect using glass spheres in vertical plastic cylinders.

Schiffer and co-workers conclude that the packing fraction increases when heating of the grains is followed by cooling - known as thermal cycling - and that the packing fraction continues to increase with multiple thermal cycles. The increase in packing fraction achieved depends on the materials from which the container and contents are made, because these may have different degrees of expansion. The results indicate that thermal cycling might provide an alternative to mechanical agitation for improved grain packing.


Peter Schiffer (Pennsylvania State University, University Park, PA, USA)
Tel: +1 814 865 5982; E-mail:


[9] Mechanism of DNA translocation in a replicative hexameric helicase (pp 270-275)

[10] Seismic reflection images of the Moho underlying melt sills at the East Pacific Rise (pp 287-290)

[11] Kruppel-like factor 2 regulates thymocyte and T-cell migration (pp 299-302)

[12] TBC-domain GAPs for Rab GTPases accelerate GTP hydrolysis by a dual-finger mechanism (pp 303-306)


***These papers will be published electronically on Nature's website on 19 July at 1800 London time / 1300 US Eastern time (which is also when the embargo lifts) as part of our AOP (ahead of print) programme. Although we have included them on this release to avoid multiple mailings they will not appear in print on 20 July, but at a later date.***

[13] A genomic code for nucleosome positioning
DOI: 10.1038/nature04979

[14] Mechanism limiting centrosome duplication to once per cell cycle
DOI: 10.1038/nature04985


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.

Sao Paulo: 1

Geulph: 3

Addis Ababa: 5

Paris: 10

Bonn: 2

Andrha Pradesh: 6

Rehovot: 13

Barcelona: 4

Cambridge: 10
Durham: 10
Keele: 2
Leeds: 5
Liverpool: 2
London: 4, 5
Manchester: 2
Oxford: 5
Preston: 2
Southampton: 10

Tucson: 6

La Jolla: 10
Stanford : 14

Greeley: 3

Evanston: 7, 13

West Lafayette: 7

Greenbelt: 1

Cambridge: 1
Worcester: 12

Minneapolis: 11

New Mexico
Santa Fe: 4

New York
Cold Spring Harbor: 9
Rochester: 5

North Carolina
Durham: 4

Cincinnati: 11

Pittsburgh: 6
University Park: 8

Austin: 6

Milwaukee: 6


For North America and Canada
Katie McGoldrick, Nature Washington
Tel: +1 202 737 2355; E-mail:

For Japan, Korea, China, Singapore and Taiwan
Rinoko Asami, Nature Tokyo
Tel: +81 3 3267 8751; E-mail:

For the UK/Europe/other countries not listed above
Helen Jamison, Nature London
Tel: +44 20 7843 4658; E-mail

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