Axolotls: The salamanders that snack on each other (but don't die) - Luis Zambrano

譯者: Camila Lin 審譯者: Helen Chang

In 1864, French zoologist August Duméril

1864年，法國動物學家 奧古斯特·杜梅里爾

was baffled while investigating the axolotl.

在研究墨西哥鈍口螈時， 感到非常困惑。

Unlike many other amphibians, which transform into terrestrial adults,

不像許多其他的兩棲動物， 會經歷完全變態，成為陸生成年體，

axolotls retain their juvenile characteristics and never leave the water.

墨西哥鈍口螈保持著幼時特徵， 且終其一生都住在水中。

In an attempt to induce metamorphosis,

為了誘導牠們開始變態，

Duméril spent months removing their gills.

杜梅里爾花了好幾個月， 把牠們的鰓切掉。

But in most instances, the axolotls simply... grew them back.

但在大多數的情況下， 牠們就只是把鰓再長回來。

Indeed, axolotls are masters of regeneration:

確實，墨西哥鈍口螈是再生大師，

they can flawlessly regenerate body parts

從被截斷的四肢、粉碎的脊椎， 到部分的眼睛和大腦，

ranging from amputated limbs and crushed spines to parts of their eyes and brains.

牠們都能完美再生。

So how do they do it? And what other secrets are they keeping?

所以牠們是怎麼做到的？ 牠們還藏著甚麼秘密？

This extraordinary salamander is native to the wetlands in Mexico City.

這種超乎尋常的蠑螈， 是墨西哥市沼澤中的原生種。

Ancient Aztec people considered it the incarnation of a God named Xolotl—

古阿茲特克人認為 牠們是索洛科爾神的化身，

hence the axolotl’s name, roughly meaning “water monster.”

因此牠們的名字取自神之名， 大概的意思是「水中怪物」。

Axolotls reach sexual maturity with gills and a tadpole-like dorsal fin.

達到性成熟時，墨西哥鈍口螈 仍保有鰓和蝌蚪那樣的背鰭。

Scientists think their forever-young condition, called “neoteny,”

科學家認為，牠們之所以進化出這種 被稱做「幼齡延長」的永恆青春狀態，

evolved because of their stable habitat.

是由於牠們棲息的棲地十分穩定。

For salamanders that develop in waters that dry up,

對那些在會乾涸的水體中 成長的蠑螈而言，

efficiently transitioning to land is essential.

以高效率過渡到岸上，是相當必要的。

But the lakes axolotls evolved in were unchanging year-round

但墨西哥鈍口螈棲息的湖， 一年四季都毫無變化，

and didn't host many aquatic predators.

也沒多少水生掠食者。

So, scientists think it was advantageous for axolotls

所以科學家認為， 對墨西哥鈍口螈來說，

to forgo the demands of metamorphosis.

放棄變態反而更具優勢。

However, they haven’t completely lost this ability.

但是，牠們並未完全失去變態能力，

If exposed to certain substances, axolotls will turn into adults.

如果讓牠們接觸某些特定物質， 牠們就會轉大人，

But they’ll often experience shorter lifespans

但常會經歷縮短的生命週期，

and lose some of their self-healing abilities.

也會失去一部分的自癒能力。

These regenerative talents may seem like crazy superpowers to begin with,

雖然這些再生能力一開始 看起來像是瘋狂的超能力，

but axolotls have good use for them.

但對墨西哥鈍口螈來說卻很有用。

As babies, they’re in direct competition.

在幼兒時期，牠們是直接競爭的關係，

So, they snack on each other.

所以，牠們會把彼此當成點心。

This is usually not a huge problem thanks to how quickly

多虧牠們超快的重生能力，

they can regenerate body parts.

這通常也不是甚麼大問題。

When an axolotl loses a limb, tissues stimulate growth in the area.

當墨西哥鈍口螈失去某條四肢後， 組織會刺激那個部位的生長。

Skin cells divide and cover the wound.

皮膚細胞會分裂並包覆傷口，

Then, progenitor cells, which can develop into various bodily tissues,

接著，能長成多種 身體組織的先驅細胞，

form a mass at the site of injury

會在受傷部位形成巨集，

and nearby nerves secrete growth-promoting proteins.

鄰近的神經則分泌 促進生長的蛋白質，

Over the next few weeks, a new limb emerges

在接下來的幾個禮拜內， 隨著細胞和諧地增殖、分化，

as cells proliferate and differentiate in coordination.

新的肢幹就會生成。

This process could potentially lead to uncontrolled growth and tumor formation.

再生過程可能會導致 生長暴衝或生成腫瘤，

But axolotls are remarkably resistant to cancer.

但墨西哥鈍口螈卻對癌症很有抵抗力。

They have a system in place that tightly controls cellular proliferation.

牠們內建一個可用的系統， 能精密控制細胞增殖。

To better understand the axolotl’s baffling biology,

為了更了解令人困惑的 墨西哥鈍口螈生物學，

scientists sequenced its genome.

科學家定序出牠們的基因組，

They found it to be more than ten times longer than a human’s.

發現牠們的基因組長度 是人類的十倍多。

Mutations can change the length of any animal’s genome.

突變可以改變任何動物的基因組長度，

For whatever reason, salamanders have much more DNA than other vertebrates

無論出於何種原因， 蠑螈常失去一部分的 DNA ，

because they lose parts of it less frequently.

所以牠們的 DNA 比其他脊椎動物來得多。

Investigating the axolotl’s genome, scientists saw many repeated sequences,

研究墨西哥鈍口螈的基因組時， 科學家們發現許多重複的序列，

most of which don't code for proteins and have no known function.

大多數的序列不編碼 蛋白質，功能也不清楚。

They also found genes that are key in regeneration.

科學家也發現了重生的關鍵基因。

However, the biggest factor that sets axolotl regeneration apart

但是，讓牠們的重生 與眾不同的最重要因子，

may not be a set of unique genes, but how they regulate their genes.

可能不是一串獨特的基因， 而是牠們如何控管自己的基因。

It’s no wonder that axolotls are one of science’s most studied animals.

蠑螈是科學界研究最多的 動物之一也就不足為奇了。

But their population in the wild has plummeted.

但野生墨西哥鈍口螈的族群

已大幅減少。

Hundreds of years ago, axolotls thrived under the Aztec capital.

幾百年前，墨西哥鈍口螈 在阿茲特克首都治下大量繁衍。

Within the surrounding lakes,

阿茲特克人在周圍的湖泊上，

Aztec people built islands called chinampas for growing crops.

建造名為「奇南帕」的浮島， 用以種植穀物。

This highly productive form of agriculture created a vast system of canals,

這種高產能的農耕方式， 創造了廣大的渠道系統，

expanding the lake system’s shallow, sheltered habitat—

擴大湖泊本身淺而充滿庇護的棲地，

the axolotls’ ideal environment.

對墨西哥鈍口螈來說，是理想的環境。

But when Spanish invaders arrived, they began draining the lakes.

但西班牙侵略者入侵後， 開始抽取湖水，

And even more water has been diverted in recent years.

近幾年，又有更多水流被轉向。

Today, the entire population of wild axolotls is found in just one place,

今天，能找到野生墨西哥鈍口螈 族群的地方，只有一個，

Lake Xochimilco, where it’s threatened by pollution and invasive fishes.

就是索契米爾科湖，但牠們卻受到 汙染與入侵種魚類威脅。

People are working to regenerate the ecosystem

人們正在努力使生態系統再生，

and strengthen the 2,000 year old chinampa farming tradition.

也在加強已有兩千年歷史的 「奇南帕」耕種傳統。

If interest grows, farmers could recover abandoned chinampas

如果興趣提高，農夫們能重建 被拋棄的「奇南帕」，

and support the local community— along with the axolotl.

支持當地社群， 同時保護墨西哥鈍口螈。

Eventually, the benefits of saving this salamander might be even greater.

最終，拯救這種蠑螈 或許能為我們帶來更大的好處。

Scientists hope that one day we’ll be able to apply

科學家期望，有一天能將

the axolotl’s masterful tumor suppression and regenerative abilities

牠們精湛的腫瘤抑制能力及重生能力，

to the human body.

運用在人體身上。

Perhaps its secrets are the real reason for the slimy god monster’s smile.

或許這些秘密，就是這種黏糊神獸 之所以微笑的理由呢。