Volume 442 Number 7100 pp223-328 (20 July 2006) 封面故事：食物链的复杂性与稳定性
食物链网络所反映的是哪些生物吃另一些生物，可用来直观反映生物群落的组织。食物链网络是复杂的，达尔文也认识到了这一点，他曾形象地将一个食物链网络比作一个“错综复杂的河岸，它被很多种类的很多植物所覆盖，有鸟儿在灌木丛上鸣唱，有各种各样的昆虫飞来飞去，还有蠕虫在潮湿的土中爬行”。本期封面图片（由Sergi Valverde用Netlab软件绘制，）所反映的是一个根据经验绘制的食物链网络的复杂性，其中的物种是与英国Silwood公园的金雀花相关的物种。Montoya等人对最近关于生态网络的研究工作进行了评述，并对一个矛盾现象进行了分析。该矛盾现象是这样的：理论预测复杂的网络是脆弱的，而复杂性却会发展变化并长期存在。他们得出的结论是，这些网络的确是复杂的，但没有复杂到我们无法了解它们的程度。在反映进食关系的图谱中有简化的模式，“错综复杂的河岸”部分地方不像其他地方那么复杂。随着模拟越来越接近实际，影响生态脆弱性的因素将会变得越来越清楚，这对关于生态影响和保护的研究工作是有好处的。（Review Article p. 259）本期Nature还刊登了反映生态问题的其他文章。在一篇参与生态系统生物多样性争论的文章中，Rooney等人发现，真实食物链网络中有一个重复出现的特征：处在食物链顶端的捕食者会将在生产力和周转率方面都不相同的明显“很快”的能量通道与明显“很慢”的能量通道耦合起来。理论分析表明，这种耦合是食物链稳定性的关键。令人吃惊的是，降低生物多样性的人类行为也会逐渐破坏赋予这种稳定性的结构。所以，现在也许是不要只关注生态系统生物多样性、而要更多关注产生食物链稳定性的因素的时候了。（Article p. 265; News and Views）我们都承认，生态问题是复杂的。但是，需要进行与生物多样性有关的决策时，政策制定者们却没有一个得到大家认可的国际专家组织向他们提供咨询。在气候变化方面，国际上有IPCC（政府间气候变化专门委员会）。现在，生态学家提出要成立IMoSEB，其全称为“International Mechanism of Scientific Expertise on Biodiversity”。(Commentary, p. 245)
关于再发新星RS Oph的观测结果
今年2月，再发新星RS Ophiuchi (RS Oph)诞生了。每隔20年左右的时间，该双星体系的白矮星就会从其红色的巨型伴星那里积聚足够多的物质，促成一次热核爆炸，这种爆炸在我们看来是其亮度由非常暗的12.5等左右增加到5等。两个小组在本期Nature上报告了对最近爆发的观测结果。Sokoloski等人利用卫星X-射线观测结果来揭示最初阶段的情况，在最初阶段，爆炸波自由向外传播。在2天时间内，向外传播的波开始慢下来，说明爆炸所产生的碎片要比从这样一次事件所预期的数量少得多。O'Brien等人利用最大的陆基射电天文望远镜阵列来对RS Oph进行观测，因而能够在最初发现14天之后首次对一个新星爆炸中的冲击波进行直接成像观测。所显示的结构表明，该天体正在向一个恒星残体发展演化，类似于一种二类超新星的演化，但它是在几个月的时间尺度上演化的，而不是在千年的时间尺度上。
一种基于石墨薄片的新型复合材料
碳纳米管非凡的机械性能来自它们由之形成的、薄至原子级的碳层（石墨薄片）的非凡强度和硬度。相比之下，大体积的石墨（一种多晶材料）断裂强度低，容易因石墨薄片的脱层发生断裂，或在晶体之间的颗粒边界上发生断裂。现在，通过将石墨薄片与石墨分开、并通过化学方法对其进行调整，Stankovich等人研制出了一种成本不高的聚合物基质复合材料，它含有散布的石墨薄片，该材料具有一系列有用的热性能、电性能和机械性能。
板块断裂造成地表裂缝
在2005年9月的一段为期15天的时间内，埃塞俄比亚阿尔法低地60公里长的一段，因超过2立方公里的熔化岩石注入进该板块中而被撕开，在地表上形成了一个8米宽的裂缝。事件前后获得的卫星雷达影像表明，这里形成了一系列裂缝，裂缝两边隆起，地表沉降到了熔化的岩石上。这一系列事件在过程上与发生在冰岛Krafla 的事件相似，说明大陆板块断裂曾经在阿尔法低地发生过，在板块断裂过程中，中海洋山脊特征性的轴向分割开始出现。
副突变是RNA引导的
副突变是上个世界50年代首次在玉米中发现的，此后曾在其他植物、真菌、甚至小鼠中发现，它是一个打破常规的遗传模式。大多数情况下，孟德尔的遗传法则是得到遵守的，基因对独立遗传。副突变是一种相互作用，在这个过程中，一种基因的一个沉默的等位基因将另一个“积极表达”的等位基因变异，所以它也被沉寂。现在，利用玉米所做的新的研究工作表明，副突变是RNA引导的。与副突变和转位子沉寂相关的染色质状态的稳定性要求mop1基因，它为一个依赖于RNA的RNA聚合酶编码。
KLF2的一种新功能
转录因子KLF2长期被认为在控制成熟T细胞的存活和静止中扮演一个关键角色，因为缺乏KLF2的T细胞会在胸腺中形成，但不能进入周围淋巴器官。一项新的研究工作对这种表现型提出了另一种解释，这种解释与KLF2作为胸腺细胞和T细胞迁移的一个调控因子这样一个完全不同的功能是一致的。 KLF（Krüppel类转录因子）家族的蛋白参与脊椎动物发育的很多方面，并且与若干疾病状态有关。KLF2这一新发现的功能与不同细胞类型的终端分异所必需的其他一些KLF是相似的。
能够对组蛋白H3进行去甲基化的酶
本期Nature上两篇论文识别出了能够从组蛋白H3的Lys 9残体上对一个三甲基官能团进行去甲基的酶，而该官能团是形成异染色质所需的一个“标志”，以前被认为是稳定的。Cloos等人发现，GASC1（JMJD2酶家族的一个成员）在过度表达时能破坏异染色质的结构，并且可能有助于肿瘤的形成。Klose等人发现，JHDM3A（也是一种JMJD2型的酶）的过度表达破坏异染色质的结构。它可能在常染色质中发挥功能，对转录进行调控。
蛋白的折叠和展开
过去，蛋白折叠通过理论研究一直要比通过实验研究更容易一些。但最近，理论已经开始被实验所证实。人们一般认为，所有蛋白都是在一个突然的动作中折叠的，但与这种看法相反的是，一些蛋白事实上是逐渐折叠和展开的，而且整个过程是在一系列被称为“下坡折叠”的步骤中进行的。Sadqi等人利用一种新颖的NMR方法来监控一个蛋白从原始状态开始一个原子一个原子地展开过程。他们获得的结果分辨率高于以前获得的结果，并且证实了折叠是一个统计过程，利用一种“下坡景观漏斗模型”可以最好地来理解它。另外，协同性可通过绘制一个蛋白内的原子相互作用来理解。
通过控制温度改变颗粒聚集程度
颗粒材料的处理和存放在很多行业中很重要，通过更好地了解造成颗粒聚集在一起的因素，有可能对相关技术进行改进。机械搅动通常在用来控制颗粒材料动态构型的体系中发挥一定作用。但新的研究工作表明，控制温度是另一种办法。在用玻璃珠所做的试验中，仅仅通过升高温度、然后再降低温度，就能诱导颗粒聚集程度的可控增加。
ContentsEditorials
WHO's in charge? p223
Global health remains firmly on the G8 agenda — for better or worse.
doi:10.1038/442223a
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Safety catch p223
Risk assessment is a useful environmental tool, but not if it is used as a cover for a deregulatory agenda.
doi:10.1038/442223b
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Save the lungfish p224
An Australian dam project threatens a living fossil.
doi:10.1038/442224a
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Research Highlights
Research highlights p226
doi:10.1038/442226a
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News
Moving towards a graphene world p228
Synthesis paves way for industrial applications.
Richard Van Noorden
doi:10.1038/442228a
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It's legal: Italian researchers defend their work with embryonic stem cells p229
Scientists respond to cardinal's call for excommunication.
Jacopo Pasotti and Ned Stafford
doi:10.1038/442229a
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Sidelines p230
doi:10.1038/442230a
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Concerns grow over secrecy of bubble-fusion inquiry p230
University investigation criticized for lack of transparency.
Eugenie Samuel Reich
doi:10.1038/442230b
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From aircraft engineer to FBI suspect p232
Plasma physicist falls foul of US export controls.
Geoff Brumfiel
doi:10.1038/442232a
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Dam project threatens living fossil p232
Lungfish face extinction, say environmentalists.
Helen Pearson
doi:10.1038/442232b
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'You can't have a mission without a camera' p234
A sister of the Mars Express probe has made it to Venus. And scientists have travelled to Beijing to discuss its first results. Horst Uwe Keller, who is presenting images from the craft's camera, spoke to Nature from the meeting.
Jenny Hogan
doi:10.1038/442234a
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News in brief p235
doi:10.1038/442235a
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Correction p235
doi:10.1038/442235b
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Business
Stuck in the middle p237
The first foreign-based biotech company to list its shares in Japan has been caught up in bureaucracy — but its experience should help others. Ichiko Fuyuno reports.
doi:10.1038/442237a
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News Features
Palaeoanthropology: Decoding our cousins p238
DNA extracted from bones could shed light on what happened when our ancestors crossed paths with Neanderthals. But not everyone can get the fossils out of the ground, as Rex Dalton learns.
doi:10.1038/442238a
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Safe and sound? p242
The White House is trying to reform environmental and health regulation across the board. But it is doing so very quietly. Colin Macilwain takes a look behind the scenes.
doi:10.1038/442242a
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Correspondence
New Orleans was prepared but it was overwhelmed p244
Ezra Boyd
doi:10.1038/442244a
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Cells have long experience of dealing with UVC light p244
James E. Cleaver
doi:10.1038/442244b
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Same colour, many different countries p244
Zhen-Ling Sun
doi:10.1038/442244c
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Commentary
Diversity without representation p245
For policymakers, biodiversity can present more complex challenges than climate change, argue Michel Loreau, Alfred Oteng-Yeboah and their co-authors. So why isn't there an international panel of experts for biodiversity?
doi:10.1038/442245a
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Books and Arts
Wanted: an Australian Volvo p247
Why doesn't the Lucky Country's scientific and technological strength match its natural riches?
Barry Jones reviews The Australian Miracle: An Innovative Nation Revisited by Thomas Barlow
doi:10.1038/442247a
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Renaissance man p248
Giorgio Parisi reviews Thus Spoke Galileo: The Great Scientist's Ideas and their Relevance to the Present Day by Andrea Frova and Mariapiera Marenzana
doi:10.1038/442248a
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Galileo in the gallery p248
doi:10.1038/442248b
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A drink from the magic well p249
Francis L. W. Ratnieks reviews Asian Honey Bees: Biology, Conservation and Human Interactions by Benjamin P. Oldroyd and Siriwat Wongsiri
doi:10.1038/442249a
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More on bees p249
doi:10.1038/442249b
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News and Views
Plate tectonics: Magma does the splits p251
A minor volcanic eruption in Ethiopia was the main visible clue to a massive injection of magma along the Afar rift last year. Such inconspicuous processes could have been crucial in early continental break-up.
Freysteinn Sigmundsson
doi:10.1038/442251a
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Ecology: Asymmetry and stability p252
Ecological communities are dauntingly complex. Nonetheless, ecologists gallantly persevere in eliciting insights about the factors that govern the behaviour and persistence of these messy, tangled webs.
Robert D. Holt
doi:10.1038/442252a
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Materials science: Carbon sheet solutions p254
When carbon fibres just won't do, but nanotubes are too expensive, where can cost-conscious materials scientists go to find a practical conductive composite? The answer could lie with graphene sheets.
Nicholas A. Kotov
doi:10.1038/442254a
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Microfluids: Clicks and chips p254
Joshua M. Finkelstein
doi:10.1038/442254b
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Structural biology: Proteins downhill all the way p255
The hundreds of hydrogen atoms in a protein can be used as reporters to describe how the protein folds into and out of shape. The results challenge the dogma that this is always an all-or-nothing process.
Jeffery W. Kelly
doi:10.1038/442255a
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50 & 100 years ago p255
doi:10.1038/442255b
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Brief Communications
Granular materials: Packing grains by thermal cycling p257
Small temperature changes can affect the packing of granular materials without mechanical disturbance.
K. Chen, J. Cole, C. Conger, J. Draskovic, M. Lohr, K. Klein, T. Scheidemantel and P. Schiffer
doi:10.1038/442257a
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Corrigendum p257
doi:10.1038/442257b
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Brief Communications Arising
Earth science: Is earthquake rupture deterministic? pE5
Paul Rydelek and Shigeki Horiuchi
doi:10.1038/nature04963
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Earth science: Is earthquake rupture deterministic? (Reply) pE6
Erik L. Olson and Richard M. Allen
doi:10.1038/nature04964
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Review
Ecological networks and their fragility p259
José M. Montoya, Stuart L. Pimm and Ricard V. Solé
doi:10.1038/nature04927
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Articles
Structural asymmetry and the stability of diverse food webs p265
Neil Rooney, Kevin McCann, Gabriel Gellner and John C. Moore
doi:10.1038/nature04887
Abstract | Full Text | PDF (245K) | Supplementary information
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Mechanism of DNA translocation in a replicative hexameric helicase p270
Eric J. Enemark and Leemor Joshua-Tor
doi:10.1038/nature04943
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Letters
An X-ray-emitting blast wave from the recurrent nova RS Ophiuchi p276
J. L. Sokoloski, G. J. M. Luna, K. Mukai and Scott J. Kenyon
doi:10.1038/nature04893
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An asymmetric shock wave in the 2006 outburst of the recurrent nova RS Ophiuchi p279
T. J. O'Brien, M. F. Bode, R. W. Porcas, T. W. B. Muxlow, S. P. S. Eyres, R. J. Beswick, S. T. Garrington, R. J. Davis and A. Evans
doi:10.1038/nature04949
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Graphene-based composite materials p282
Sasha Stankovich, Dmitriy A. Dikin, Geoffrey H. B. Dommett, Kevin M. Kohlhaas, Eric J. Zimney, Eric A. Stach, Richard D. Piner, SonBinh T. Nguyen and Rodney S. Ruoff
doi:10.1038/nature04969
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Seismic reflection images of the Moho underlying melt sills at the East Pacific Rise p287
S. C. Singh, A. J. Harding, G. M. Kent, M. C. Sinha, V. Combier, S. Bazin, C. H. Tong, J. W. Pye, P. J. Barton, R. W. Hobbs, R. S. White and J. A. Orcutt
doi:10.1038/nature04939
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Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode p291
Tim J. Wright, Cindy Ebinger, Juliet Biggs, Atalay Ayele, Gezahegn Yirgu, Derek Keir and Anna Stork
doi:10.1038/nature04978
First paragraph | Full Text | PDF (421K) | Supplementary information
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An RNA-dependent RNA polymerase is required for paramutation in maize p295
Mary Alleman, Lyudmila Sidorenko, Karen McGinnis, Vishwas Seshadri, Jane E. Dorweiler, Joshua White, Kristin Sikkink and Vicki L. Chandler
doi:10.1038/nature04884
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Kruppel-like factor 2 regulates thymocyte and T-cell migration p299
Corey M. Carlson, Bart T. Endrizzi, Jinghai Wu, Xiaojie Ding, Michael A. Weinreich, Elizabeth R. Walsh, Maqsood A. Wani, Jerry B. Lingrel, Kristin A. Hogquist and Stephen C. Jameson
doi:10.1038/nature04882
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TBC-domain GAPs for Rab GTPases accelerate GTP hydrolysis by a dual-finger mechanism p303
Xiaojing Pan, Sudharshan Eathiraj, Mary Munson and David G. Lambright
doi:10.1038/nature04847
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The putative oncogene GASC1 demethylates tri- and dimethylated lysine 9 on histone H3 p307
Paul A. C. Cloos, Jesper Christensen, Karl Agger, Alessio Maiolica, Juri Rappsilber, Torben Antal, Klaus H. Hansen and Kristian Helin
doi:10.1038/nature04837
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The transcriptional repressor JHDM3A demethylates trimethyl histone H3 lysine 9 and lysine 36 p312
Robert J. Klose, Kenichi Yamane, Yangjin Bae, Dianzheng Zhang, Hediye Erdjument-Bromage, Paul Tempst, Jiemin Wong and Yi Zhang
doi:10.1038/nature04853
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Atom-by-atom analysis of global downhill protein folding p317
Mourad Sadqi, David Fushman and Victor Muñoz
doi:10.1038/nature04859
First paragraph | Full Text | PDF (483K) | Supplementary information
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Corrigendum: Titan Radar Mapper observations from Cassini's T3 fly-by p322
C. Elachi, S. Wall, M. Janssen, E. Stofan, R. Lopes, R. Kirk, R. Lorenz, J. Lunine, F. Paganelli, L. Soderblom, C. Wood, L. Wye, H. Zebker, Y. Anderson, S. Ostro, M. Allison, R. Boehmer, P. Callahan, P. Encrenaz, E. Flamini, G. Francescetti, Y. Gim, G. Hamilton, S. Hensley, W. Johnson, K. Kelleher, D. Muhleman, G. Picardi, F. Posa, L. Roth, R. Seu, S. Shaffer, B. Stiles, S. Vetrella and R. West
doi:10.1038/nature05004
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Top of pageNaturejobs
Prospect
Prospect p323
Outsourcing and European biotech companies.
Paul Smaglik
doi:10.1038/nj7100-323a
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Postdocs and Students
Making a move p324
Morale, money or moving house can all be reasons for switching labs mid-project. Kendall Powell learns from those who have made the jump with success.
Kendall Powell
doi:10.1038/nj7100-324a
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Career Views
Anne Glover, chief scientific adviser for Scotland p326
Glover becomes Scotland's chief scientific adviser.
Virginia Gewin
doi:10.1038/nj7100-326a
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From student to entrepreneur p326
Graduate student breaks into biotechnology.
Christopher Loose
doi:10.1038/nj7100-326b
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Lost and found p326
Sorting through the clutter to retain the big ideas.
Katja Bargum
doi:10.1038/nj7100-326c
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Futures
From the desk of Jarrod Foster p328
A brain implant for whatever ails you.
Biren Shah
doi:10.1038/442328a
Full Text | PDF (142K)
