克隆自我——龙纹鳌虾的故事
It sounds like a bad monster movie plot: A 10-legged mutant creature that reproduces asexually, escapes from confinement in Germany, and quietly begins a global invasion. Within 2 decades, clones of the voracious animal spread through Europe and Africa, bringing devastation to ecosystems and threatening native species.
听起来像是怪兽电影的情节：一只10条腿的可以无性繁殖的突变生物，从德国的笼子里逃出，然后默默变成了全球入侵生物。在二十年的时间里，这种贪吃的生物的克隆体就遍布了欧洲和非洲，给当地生态系统带来巨大灾难，并威胁到了本地的物种。
That appears to be the strange-but-true story of the marbled crayfish, an invasive freshwater species suspected to have been created through a reproductive accident in an aquarium around 1995.
这听起来很奇怪—却是龙纹鳌虾的真实故事，这是一种在1995年水族馆里的一次繁殖事故中诞生的入侵性的淡水虾。
A new analysis of the crustacean’s genome supports this unlikely origin and may help explain how the animal has subsequently spread and adapted to so many new environments.
对这种甲壳纲动物的最新分析证明了这种不太可能的起源，也有可能为这种动物接下来是如何散布并适应如此多样的新环境提供解释。
The crayfish’s unusual evolution could also suggest a strategy to tackle a more infamous clonal monster: cancer.
这种鳌虾不寻常的进化还可能为战胜另一种臭名昭著的克隆怪兽提供一种策略：怪兽叫做癌症。
“In many ways, the invasive expansion of [the marbled crayfish] is analogous to a cancerous lineage spreading asexually at the expense of its host,” says Jean-François Flot, an evolutionary genomicist at the Free University of Brussels who was not involved with the work.
“从很多方面来看，这种龙纹鳌虾的入侵性扩张都与癌细胞以牺牲自己宿主的代价进行无性繁殖扩增具有相似之处，”珍.弗朗索瓦.弗洛特说，她是布鲁塞尔自由大学的进化遗传学家，而她并没有参与到这项工作中。
The marbled crayfish is the only crustacean that reproduces asexually, with the all-female species making clones of itself from eggs unfertilized by sperm.
龙纹鳌虾是甲壳纲动物中唯一一个进行无性繁殖的，这个品种全为雌性，利用自身精液给卵受精后可以克隆自己。
It has been thought to have arisen when two slough crayfish, imported from Florida for the aquarium trade in Germany, mated.
据称它的出现是由于两只从弗罗里达进口用于德国的水族馆交易的沼虾交配产生。
Since its discovery in 1995 in Germany, the marbled crayfish has spread across Europe and into Africa in huge numbers.
自从1995年在德国被发现后，龙纹鳌虾从欧洲大量地传入了非洲。
“They eat anything—rotten leaves, snails or fish broods, small fish, small insects," says Frank Lyko, a molecular geneticist at the German Cancer Research Center in Heidelberg.
“它们什么都吃—腐叶，蜗牛或者鱼苗，小鱼，小昆虫”弗朗克. 莱克说，他是位于海德堡的德国癌症研究中心的分子遗传学家。
“This crayfish is a serious pest,” adds Gerhard Scholtz, an evolutionary biologist at Humboldt University in Berlin, who has tracked its rapid spread across the globe, including Madagascar, where its success threatens the existence of the seven crayfish native to that island country.
“这种鳌虾是一种可怕的害虫，”杰哈德.斯科茨补充道，他是柏林洪堡大学的进化生物学家，对它在全球的迅速扩散进行了研究，其中包括马达加斯加，在那里龙纹鳌虾威胁到了这个岛国七种当地的鳌虾。
The European Union banned the species: It must not be sold, kept, distributed, or released to the wild.
欧盟已经禁止了这个物种：不允许售卖，饲养，散布或者放生到野外。
Five years ago, Lyko became interested in the marbled crayfish, now called Procambarus virginalis, because he thought its newly evolved asexual nature might parallel how a normal cell turns cancerous and begins generating clones of itself.
五年前，莱克开始对龙纹鳌虾产生兴趣，现在它被称为Procambarus virginalis，因为他认为新进化出来的无性繁殖天性跟细胞癌变后不断自我克隆的过程很相似。
In particular, he wanted to study the genomes of marbled crayfish to uncover basic mechanisms underlying epigenetics, the binding of molecules to DNA that can drive tumor growth and help cancer spread.
特别是，他想要研究龙纹鳌虾的基因组来解释表观遗传学下面的基本机制，分子联结成DNA然后促进肿瘤生长，帮助癌症扩散的过程。
So, Lyko and his colleagues sequenced genomes of about a dozen marbled crayfish from different parts of the world and performed less detailed genetic analyses of two dozen more from across Madagascar.
于是，莱克和他的同事们对十二只来自世界上不同地方的龙纹鳌虾进行了基因测序，并对来自马达加斯加的另外两组进行了大致的遗传学分析。
At 3.5 billion DNA bases in length, the crustacean’s genome is bigger than the human genome, but contains about the same number of genes, 21,000, they report today in Nature Ecology & Evolution.
总长度达到了35亿个DNA碱基对，这种甲壳动物的基因组比人类基因组还要庞大，但基因的数量差不多相同，是21,000个，他们在今天的《自然生态与进化》杂志上发表了文章。
This is the first genome of a decapod, a group of 10-legged crustaceans that includes shrimp, lobsters, prawns, and crabs, as well as crayfish.
这是十足类里首个被研究的基因组，这种十条腿的甲壳动物还包括虾，龙虾，对虾和螃蟹，还有鳌虾。
“This [work] opens the way for comparative genomics and identification of [unique features] in this group of ecological and economically important species,” says Etienne Danchin, an evolutionary biologist at the National Institute of Agricultural Research in Sophia-Antipolis, France, who was not involved with the research.
“这就为比较基因组学和对这种对生态和经济都非常重要的物种的独特特征进行鉴定提供了一种方法，”埃蒂安.丹琴说，他是法国的索菲亚-安蒂波利斯的国家农业研究中心的进化生物学家，他并没有参与到此次的研究。
The study also “provides clues about how this genome arose and may help conservationists better track the spread of this invasive species,” Schotz says.
这项研究还“为这种基因组是如何出现的提供了线索，并有可能帮助保育学家追踪这种入侵物种的传播”，斯科茨说。
As suggested by some preliminary evidence, the marbled crayfish has three sets of 92 chromosomes, not the usual two, and each set is essentially a version of the chromosomes belonging to the slough crayfish (P. fallax).
据初步证据显示，这种龙纹鳌虾是三倍体，每组有92个染色体，不是通常的两倍体，每一组都拥有一版这种沼虾的染色体。（P.fallax）
Two of the three sets of chromosomes are virtually identical, but the third is different enough that Lyko’s team concludes the marbled crayfish likely arose from the mating of two slough crayfish from different regions of the world thrown together in an aquarium.
三组当中有两组基本上是一样的，但第三组却截然不同，因此莱克的团队得出结论说龙纹鳌虾可能是来自世界上两个不同区域的沼虾被放在了同一个水族馆里产生的。
One must have had an abnormal egg or sperm that retained two copies of its chromosomes instead of the usual single set that is in such germ cells, Lyko explains.
它的卵子或者精子必定很特别，含有两倍染色体而不是通常的生殖细胞中的一倍，莱克解释说。
The bringing together of the two distant slough crayfish enhanced the genetic variation within the new clonal “species.”
两种远缘的鳌虾组合到一起加强了这种新的克隆物种的基因多样性。
Such a union “would never happen in the wild,” he asserts.
这种组合“在野外本来是不会发生的”，他认为。
Schotz isn’t totally persuaded that the genomic pile-up happened inside an aquarium, versus two slough crayfish meeting in the wild.
斯科茨并不完全确信这种基因组合发生在水族馆里，而不是两只沼虾在野外相遇。
“It is mere speculation that it originated in captivity,” he says.
“目前还只是推测说它诞生于人工环境中，”他说。
But the analysis of marbled crayfish DNA from across Europe and Africa, he says, ”shows that all these crayfish are clones—with identical genomes the world over.”
但对来自欧洲和非洲的龙纹鳌虾进行分析后，他说，“显示所有的鳌虾都是克隆体—全世界的基因组都一样。”
More important than the crustacean’s origin may be that this clone thrives in a wide variety of freshwater habitats, with different temperatures, salinities, and acidity.
比这种甲壳动物的起源更重要的是它可以在不同的淡水环境里繁衍壮大，无论是不同的温度，盐度还是酸度。
Clones are supposed to be at a disadvantage because they lack the genetic variation to adapt to new situations.
克隆体通常被认为存在劣势因为它们缺乏适应新环境的基因多样性。
But, “This paper suggests that an animal species can rapidly invade a large geographical area despite reproducing without sex and being clonal,” Danchin says.
但，“这篇文章表示一个动物物种可以迅速入侵大片的地理区域，就算它进行无性繁殖和克隆，”丹琴说。
The marbled crayfish’s three sets of chromosomes may be key, containing enough variety for adapting to different conditions.
龙纹鳌虾的三倍染色体可能就是关键，它们含有足够的多样性可以适应不同的环境。
Danchin studies a very successful plant parasite, a nematode that reproduces asexually and also has three sets of chromosomes.
丹琴还研究了一种非常成功的植物害虫，一种可以进行无性繁殖的线虫，它也有三倍染色体。
Susan Adams, an aquatic ecologist with the U.S. Forest Service's Southern Research Station in Oxford, Mississippi, agrees.
苏珊.亚当斯，是位于牛津的美国林业局南部研究站的水族生态学家，来自密西西比，她也认同。
Work in other organisms shows that having an extra set of chromosomes can boost the number of young and may help the clones adjust to new environments.
其他组织的研究也显示拥有额外的染色体可以让幼崽更多，并可能帮助这些克隆体适应新环境。
“Greater adaptability is expected to enhance invasion success,” she says.
“超强的适应性恐怕会更容易导致入侵成功，”她说。
A further advantage, Adams says: A clone can establish a new population starting with just one individual.
还有一个好处，亚当斯说：一个克隆体可以只靠一个个体就建立起新的种群。
“It is interesting to contemplate the global, ecological implications of an exceedingly rare evolutionary event arising in someone’s aquarium.”
“想想这种某人的水族馆里发生的超级稀有的进化事件竟然有了全球的生态方面的意义，真是很有趣的。”
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