An epic bout of cold weather quickly altered a population of lizards—an example of natural selection in action. Christopher Intagliata reports.

一场世纪大寒潮迅速改变了蜥蜴群——一种实时上演的自然选择。

撰文/播音 Christopher Intagliata

翻译 张清越

审校 潘磊

In January 2014, an epic cold wave swept across the southeast—a "snowpocalypse" so severe that thousands of drivers in Atlanta abandoned their cars on icy highways and Interstates.

在2014年1月，一场被称为“末日暴雪”的大寒潮席卷了整个亚特兰大的东南地区，以至于上千名司机在冰封的高速公路和州际公路上弃车逃离。

"And I'm from the south, I was raised in South Carolina, and I can tell you that in the South we do not do cold—at all."

“我来自南方，在南卡罗来纳州长大，我所能告诉你的是在南方，我们从来感受不到寒冷。”

Shane Campbell-Staton was watching it all unfold from Harvard, where he was getting his PhD. He'd just wrapped up his last field season in Texas, studying the green anole lizard. And as he was scanning photos of the storm, he came across something unexpected: a photo that included his research subject.

沙恩·坎贝尔斯塔顿在哈佛看到了这些资料。哈佛也是他取得博士学位的地方。沙恩刚总结完成了他的上一个工作季--在德克萨斯州野外，研究绿色Anole蜥蜴（一种美国变色龙）。他在仔细检查那次风暴的照片时，遇到了一些意想不到的事物：一张给他带来研究课题灵感的照片

"There was this one picture of a green anole that was upside down, dead in the snow. And it was sort of a Eureka moment. And I thought to myself, well maybe I should go back out and see if these populations I'd been studying, if they showed any sort of response to this pretty extreme weather event in the south."

“在一张照片中记录了一只肚皮朝天死在雪地里的anole蜥蜴。那时灵光一现（Eureka moment），我当时想，我也许应该回去看看这些我一直研究着的蜥蜴物种，看看它们对南方的这次极端气候事件是否会有反应。”

And so that's what he did. Because here's the bit of serendipity: he'd actually been studying the cold tolerance of different populations of these lizards. And the cold snap had just delivered the perfect experiment—a chance to see natural selection in action.

他就那样做了。这次研究似乎碰上不错的运气：实际上，他正在研究这种蜥蜴中不同种群的耐寒性。而这次寒流恰巧给了他一场完美的实验——一次可以看着自然选择发生作用的机会。

"So I went back in April right after these winter storms had subsided. And I noticed that in the south, the southernmost population, the survivors of the storm were able to maintain function at significantly colder temperatures than the population before the storm. And this ability to maintain function at colder temperatures is something we typically see much farther north."

“所以当4月份冬季风暴消退后，我马上回去了。我发现，在南部，栖息地位置最靠南边的种群中，经历过风暴的蜥蜴，与风暴来临之前相比，能够在温度大幅降低的环境中维持身体机能。而在这种在更冷的温度下生存的能力，我们通常在栖息地更加偏北的种群里见到。”

He did genetic analyses too: and found that the genes switched on in the surviving southern lizards overlapped with genes more typically turned on in their cold-hardy northern cousins. And the survivors also carried variations in their DNA that more closely matched northern lizards. So three things: cold tolerance, gene expression, and even the gene variants the southerners carried, suggested this winter storm had indeed caused selection on the southern lizards. The analysis is in the journal Science. [Shane C. Campbell-Staton et al., Winter storms drive rapid phenotypic, regulatory, and genomic shifts in the green anole lizard]

他还对蜥蜴做了基因分析：他发现，在生存下来的南方蜥蜴身上发生变化增加的新基因与抗寒能力较强的北方蜥蜴的有重合。而且，活下来的南方蜥蜴基因中还发生了向北方蜥蜴的变异。因此有三点：耐寒性、基因表达、甚至南方蜥蜴所发生的基因变异表明，这场冬季寒潮确实导致在南方蜥蜴种群内部的自然选择。这项分析报告发表在《科学》杂志上。

Campbell-Staton, now at the University of Illinois and the University of Montana, is quick to mention that this isn't quite evolution yet. It's just one generation—he hasn't yet seen these traits passed down to another set of lizards. That's his next investigation.

目前在伊利诺伊大学和蒙大拿大学从事研究的坎贝尔·斯塔顿很快就指出，这还不构成“进化“。这种变化只表现在一代蜥蜴身上——他还没有看到遗传到其他世代的蜥蜴身上。而这将是他的下一个研究项目。

As for whether this is a good thing, the fact that some lizards were able to summon the ability to survive cold? "The answer is both yes and no potentially." Yes, because if another cold wave rolls through, the surviving southern population will be better prepared—more cold-tolerant.

至于一些蜥蜴为了生存能够激发出耐寒能力，这是不是一件好事呢？ “答案既是肯定的，也是否定的。” 是，是因为如果再发生一次寒潮风暴，能活下来的南方蜥蜴将会做好准备——更强的耐寒性。

But: "We know that selection comes at a cost. Which is death. So the individuals that died during this event may have had genetic variants that would have allowed them to survive a heat wave, or a drought, or some other extreme event. And now those lineages are essentially gone."

但是:“我们知道，自然选择是要付出代价的，代价即死亡。因此，在这次事件中，死亡的那些蜥蜴所携带的基因变异，可能是让他们在热浪、干旱或其他极端气候事件中存留的关键。而现在这些血统基本上消失了。”

The long term forecast for the 21st century includes more of these extreme events—and more severe ones at that. So species that lose their genetic Swiss army knife of adaptive tools may, again, be left out in the cold.

21世纪的气候长期预测中包含更多的这些极端事件——其中还有比这次寒潮更严重的。多种多样的基因是物种应对那些极端天气的瑞士军刀，每一种都有作用。那些失去了对应适应基因的物种，可能会在下次寒潮中出局死去。