经济学人下载:水产养殖--鱼食界的哥斯拉(2)

Rotifers are famously asexual. The last time members of one group of the animals, the bdelloids, had sex is reckoned by zoologists to have been about 80m years ago. Members of Brachionus plicatilis are not as sex-starved as that, but they still reproduce for the most part by parthenogenesis. Indeed, the variety Dr Abe chose to work with, known as the Notojima strain, is, like the bdelloids, an obligate parthenogen. For this sort of mutagenic work, however, parthenogenesis is an advantage. It means that a successful mutated line of rotifers will not be diluted by the genetic mixing caused by sexual congress. 

轮虫的无性繁殖是出了名的。据动物学家估计，蛭形类动物的最后一次交配发生在大约8000万年前。褶皱臂尾虫的成员并没有那么地“性饥渴”，但它们仍多半通过单性生殖进行繁殖。事实上，安博士选择研究的品种(被称为能登品种)就像蛭形虫一样是专性单性生殖。然而，对于这种突变工作来说，单性生殖是一种优势。这意味着一个成功的轮虫突变系不会被有性繁殖引起的基因混合所稀释。

The Notojima strain is the largest L rotifer used by Japanese fish farmers. In her quest to make it larger still, Dr Abe exposed batches of the animals to ion beams of various strengths and compositions, and then put the survivors through three rounds of proliferation and selection of the largest of their offspring, to try to come up with the Godzillas of the rotifer world. 

日本养鱼户使用的最大的L轮虫品种是三岛品种。为了使其更大，阿部博士将几批轮虫暴露在不同强度和组成的离子束当中，然后让存活下来的轮虫进行三轮繁殖并选择其中最大的后代，造出“轮虫界的哥斯拉”。

The upshot, out of more than 3,000 mutant strains that were larger than normal, was three promising lines which, at 350-370 microns long, nicely plug the size gap, and which are also more fecund than their ancestors. Both of these characteristics make the new strains ideal for use as fish food, and three subsequent years of study have shown them to be stable. Godzilla may be fictional. But the idea that radiation, used carefully, can create animals that are giants of their kind, is not. 

结果，在超过3000个比正常突变品种大的突变品种中产生了3个有希望的突变系，它们有350-370微米长，正好填补了大小差距，而且比它们的祖先更多产。这两种特性使新品种成为了理想的鱼食，并且随后三年的研究表明它们是稳定的。哥斯拉或许是虚构的，但“辐射(谨慎使用)能创造出同类中的巨型怪”这一观点名副其实。