古代长毛象的基因复活，以了解物种的最后日子

古代长毛象的基因复活，以了解物种的最后日子

Researchers have resurrected the genes of a tiny population of ancient woolly mammoths that mysteriously died out some 4,000 years ago on Wrangel Island, a remote 125-kilometer-wide (78-mile) Arctic refuge located off the coast of Siberia. It is likely that this group was among the last in the world.

研究人员重新发现了一小群远古长毛猛犸象的基因，这些长毛猛犸象大约在4000年前神秘地消失在弗朗格尔岛上。这个群体很可能是世界上最后的群体之一。

Madison Dapcevich

During the Ice Age, Wrangel Island was connected to Beringia and modern-day Alaska and Canada via the Bering Land Bridge. Mammuthus primigenius were among the most abundant species adapted for cold weather, but as temperatures rose in the millennia following the Pleistocene, the bridge was eventually engulfed by rising seas, forever isolating the Wrangel Island mammoths.

在冰河时代，弗兰格尔岛通过白令海峡陆桥与白令海峡、现在的阿拉斯加和加拿大相连。Mammuthus primigenius是适应寒冷天气最丰富的物种之一，但随着更新世之后的数千年温度的上升，这座桥最终被上升的海洋吞没，永远地隔离了弗兰格尔岛猛犸象。

Dramatic environmental changes associated with a warming planet saw the loss of dry steppe tundra, also known as Mammoth steppe, as the world entered the Holocene. A number of other cold-adapted species were also lost, including cave bears and hyenas as well as woolly rhinoceros. Meanwhile, mammoths went extinct in two waves, which saw mainland populations first die out, followed by those that inhabited St. Paul Island (5,600 years ago).

当世界进入全新世时，与全球变暖相关的剧烈环境变化导致了干燥草原苔原(也称猛犸象草原)的消失。许多其他适应寒冷的物种也消失了，包括洞穴熊、土狼以及长毛犀牛。与此同时，猛犸象的灭绝分为两波，首先是大陆种群的灭绝，接着是居住在圣保罗岛的种群的灭绝(5600年前)。

The new research builds on evidence that the last mammoths on Wrangel Island suffered from a variety of genetic defects. Rebecca Farnham/University at Buffalo

The Wrangel Island mammoths held on until a “fairly abrupt” extinction event wiped them out 4,600 years ago. To determine what that catastrophic event might have been, a collaborative team of researchers from several US-based universities compared the DNA of Wrangel Island mammoths to three Asian elephants and two other ancient mammoth populations. Specific genetic mutations unique to Wrangel Island mammoths were identified, each thought to play a role in important functions, like neurological development, male fertility, insulin signaling, and sense of smell. These altered genes were synthesized and placed into cells in Petri dishes for researchers to test whether the genes would function normally.

弗兰格尔岛的猛犸象坚持了下来，直到4600年前一次“相当突然”的灭绝事件才将它们灭绝。为了确定这一灾难性事件可能是什么，来自美国几所大学的一个合作研究小组将弗兰格尔岛猛犸象的DNA与三头亚洲象和另外两种古代猛犸象进行了比较。弗兰格尔岛猛犸象特有的特定基因突变被发现，每一种突变都被认为在重要的功能中发挥作用，如神经发育、男性生育能力、胰岛素信号和嗅觉。这些被改变的基因被合成并放入培养皿中的细胞中，以供研究人员测试这些基因是否能正常工作。

In short, they did not.

简而言之，它们并不能。

"Our results suggest that once populations get small they harbor deleterious mutations, once those mutations are there they will affect the ability of the population to thrive. Even if the population were to recover large numbers the mutations are still there, dragging the population down," study author Vincent Lynch, from the University of Buffalo, told IFLScience.

“我们的研究结果表明，一旦种群数量减少，它们就会产生有害的突变，一旦这些突变出现，它们就会影响种群兴旺的能力。即使种群数量大量恢复，突变仍然存在，将种群拉低，”布法罗大学的研究作者文森特·林奇告诉IFLScience。

It is believed that the environmental conditions would have gradually killed off the Wrangel Island mammoths, dwindling their already isolated population. Individuals that survived would have bred with others over generations, eventually reducing the genetic pool and eliminating the ability for a species to “breed out” harmful genetic mutations, write the researchers in Genome Biology and Evolution.

据信，环境条件会逐渐杀死弗兰格尔岛的猛犸象，减少它们已经孤立的种群。研究人员在《基因组生物学与进化》杂志上撰文称，幸存下来的个体会在几代人的时间里与其他个体交配，最终减少基因库，并消除一个物种“繁殖”出有害基因突变的能力。

"Evolution is only really effective in large populations," added Lynch, adding that as populations "get smaller, the ability of selection to remove bad mutations – and select for the good ones – is decreased because the strength of randomness is greater than selection."

林奇补充说:“进化只有在大种群中才真正有效。”他还补充说，随着种群“变小，淘汰不好的突变并选择好的突变的能力就会减弱，因为随机的力量大于选择。”

The final nail on the Wrangel Island mammoth coffin remains mysterious, but the authors note that it is clear that it is likely no coincidence that the population declined shortly after isolation. The findings build on an understanding of the final days of the mammoths, highlighting that the last of their kind likely suffered from a variety of genetic effects that hindered their development, reproduction, and ability to smell. Lynch notes that there are several limitations associated with the study.

弗兰格尔岛猛犸象棺木的最后一颗钉子仍然是个谜，但作者指出，很明显，猛犸象的数量在隔离后不久就减少了，这可能不是巧合。这些发现建立在对猛犸象最后的日子的理解之上，强调它们最后的种类可能遭受了各种各样的遗传影响，这些影响阻碍了它们的发育、繁殖和嗅觉能力。林奇指出，这项研究有几个局限性。

"Alas, we have only one Wrangel Island genome. It could be some of these mutations are unique to that individual rather than the population. More genomes would help us know this. Also, we don't have mammoth cells to test these genes in, so maybe the mammoth cells had ways to minimize the deleterious mutations we found," he said.

“唉，我们只有一个弗兰格尔岛基因组。可能这些突变中有一些是个体特有的而不是群体特有的。更多的基因组将帮助我们了解这一点。另外，我们没有猛犸象细胞来测试这些基因，所以也许猛犸象细胞有办法将我们发现的有害突变最小化。”他说。

Even so, Lynch tells IFLScience that this is a “cautionary tale” for living species threatened with extinction who may face similar genetic challenges in the generations to come.

即便如此，林奇告诉IFLScience，这对那些面临灭绝威胁的物种来说是一个“警示故事”，这些物种可能在未来几代面临类似的基因挑战。