Small Fish Takes Fast Evolution Track

小鱼快进化

Stickleback fish in Alaska evolved from living in seawater to freshwater in just 50 years, with the help of freshwater traits in their genome. 

得益于基因中的适应淡水的特征，阿拉斯加棘鱼仅用了50年就完成了从海水到淡水的进化。

撰文/播音 克里斯托弗·因塔利亚塔（Christopher Intagliata）

翻译 Meatle

审校 邰伦玥

March 27th, 1964: the world's second-most powerful recorded earthquake hits Alaska. <> 

1964年3月27日，有史以来第二强的地震袭击了阿拉斯加。

【纪实电影片段：在阿拉斯加最大的城市，安克雷奇，地震导致了建筑的崩塌。道路与房屋被大地吞噬…而在阿拉斯加湾，地震仿佛使海底下沉，然后又上升50尺，掀起了扑向海岸的巨大波浪。】

"What happened was the whole Gulf of Alaska and Prince William Sound just sort of tilted, and so near shore, near Alaska, that region sank. And then out at sea, the sea floor raised up." Susie Bassham, a molecular biologist at the University of Oregon. "And so things that were submarine platforms before suddenly were lifted above sea level, and then silt could come in and build more island."

“地震似乎导致了整个阿拉斯加湾和威廉王子海峡的倾斜，进而阿拉斯加附近的海岸往下沉降，同时外面的海底上升。”来自俄勒冈大学的分子生物学家，苏西·巴珊姆如是说，“这使以前是海底的地方突然被提升到海平面以上，泥沙得以聚集，形成更多的海岛。”

And with more island, came new freshwater ponds. Those newly created bodies of water turned out to be the testbed for a natural evolutionary experiment on a finger-sized fish, called the three-spined stickleback. Saltwater fish went in… freshwater fish came out. "Big silvery well-armored fish entered freshwater ponds. And during the last 50 years they changed their size, their coloration, they changed the size of their eyes, the length of their spines, many aspects of their skeletons, feeding structures, swimming structures, and became more stereotypical freshwater fish." But how?

同时，更多的海岛也带来了新的淡水池塘。这些新生的水体变成了一种鱼类的自然进化实验平台。这种手指大小的鱼，被称为三刺鱼。这种海水鱼类在新生水体中，变成了淡水鱼类。“大型的身披银甲的鱼进入了这些淡水池塘。在过去的50年中，它们改变了身体的大小、颜色；它们的眼睛大小、棘刺长度、骨骼构造、饮食结构和游泳姿态都变得更为接近典型的淡水鱼。”但，这种变化是怎样发生的？

Bassham and her colleagues ran statistical analyses on the genomes and body measurements of fish living in those freshwater ponds today. And they found that the saltwater versions of the fish may have actually colonized those freshwater ponds on the study islands at least six times in the last 50 years. They were able to move in and rapidly adapt because the sea-dwelling fish have a sort of "sleeper genome" of freshwater traits, just waiting to be activated. 

巴珊姆和她的同僚对居住在淡水池塘中的鱼进行了基因与身体测量，并以此为基础进行了数据分析。她们发现，在被研究的海岛上，过去的50年间，活在海中的三刺鱼确实移居到了淡水水塘中。这至少发生了6次。它们之所以能进入并快速适应淡水环境，是因为海生的鱼含有能适应淡水环境的“沉睡基因”，这些基因一旦被激活就能表现出来。

"These are anadromous fish that have been invading freshwater ecosystems over and over and over. And all those freshwater adaptations have trickled back into the sea, allowing the oceanic population, which is believed to be the ancestor of all the freshwater populations, to maintain this huge resource of differently, alternately adapted genotypes that are just waiting to get back into a freshwater system." And when they do, it takes just several dozen generations—instead of thousands of years—for this evolution to occur. The findings are in the Proceedings of the National Academy of Sciences. 

“这些溯河产卵的鱼已经一而再、再而三地进入淡水生态系统。那些适应淡水的特性又已经回溯到大海中，使作为所有淡水鱼的祖先的海水鱼类能够维持高度多样并广泛适应的基因库，为海水鱼类随时回到淡水环境做好准备。”而当它们回到淡水环境，只需仅仅数十代——而不是上千年——就能完成这些转化。这个发现发表在《美国国家科学院学报》上。

Not all species, of course, have a genome that makes it easy to respond to sudden environmental challenges, the kind we’re seeing with climate change. "For instance corals are very adapted to live in a very narrow temperature range. And there is no genetic diversity to call upon there." But there may be a few species, she says, in possession of the kind of genetic toolkit that enables sticklebacks to deal with adversity so swimmingly.

当然，并不是所有的物种都有使其快速适应环境突变的基因组，特别是在气候变化方面。“比如珊瑚虫就只能适应相当窄的温度范围。而且它们的基因多样性也没有在这方面有所表现。”然而，巴珊姆认为，可能存在一些物种，它们的基因组使到它们能像棘鱼一样，灵活地应对环境变化。