Why were scientists so obsessed with these frogs? - Carly Anne York

譯者: 穎君 紀 審譯者: Helen Chang

From the 1930s well into the 1960s,

1930 年代到 1960 年代，

pregnancy testing required a slippery piece of equipment:

女性驗孕測試作業必須使用

a female African clawed frog.

母非洲爪蟾。

For decades, hospitals and research labs around the world

醫院和實驗室長久以來

had a trusted supply of these handy amphibians,

都有穩定的貨源提供這種青蛙，

employing their help in testing for pregnancy

他們把非洲爪蟾拿來驗孕，

and in numerous other scientific endeavors.

做許多科學實驗。

So, what makes these phenomenal frogs so special?

為何非洲爪蟾會這麼被科學家愛用？

The remarkable features of the African clawed frog

從 19 世紀起就有科學家熱衷於研究

have fascinated researchers since the 19th century.

非洲爪蟾的某些特質。

We often think of frogs as hopping around to snatch up bugs

我們印象中的青蛙都是到處蹦蹦跳跳，

with their lengthy tongues.

伸出長長的舌頭把蟲捲進嘴裡。

But this water-dwelling species is almost exclusively aquatic,

但是非洲爪蟾這種在水裡生活的青蛙， 幾乎可說是完全水生，

having adapted primarily for swimming rather than crawling or jumping.

比起爬行或蹦跳，更習慣游泳。

Weirder still, African clawed frogs have no tongues at all.

更奇怪的是非洲爪蟾竟然沒有舌頭，

Instead, they suck food directly into their mouths

牠們直接把食物吸進嘴巴，

or use their hands to catch larger animals

如果獵物大一點的話， 牠們會用手抓住，

which they tear apart with powerful hind claws.

用強力的腳爪撕成小塊。

To help get close to their prey,

為了讓牠們順利接近獵物，

their smooth skin can quickly change color to blend into their surroundings.

牠們光滑的皮膚能變成 和周遭一樣的顏色。

This camouflage ability was particularly interesting to a trio of biologists

在 1920 年代的非洲， 牠們的變色能力

in South Africa during the 1920s.

引起三位科學家的注意：

Hillel Shapiro, Harry Zwarenstein, and their teacher, Lancelot Hogben,

希勒爾・夏皮羅、亨利・茲瓦倫斯汀， 和他們的老師蘭斯洛特・霍格本

were researching what role the pituitary gland,

正在研究青蛙腦裡的一小個腦垂腺

a small region of the frog’s brain,

might play in the color changing mechanism.

跟變色機制的關係。

Removing the gland altogether impaired the frogs’ ability to camouflage.

移除非洲爪蟾的腦垂腺後 牠們就不能變色，

But when Hogben injected them with a pituitary extract derived from an ox,

但霍格本把公牛的腦垂腺 分泌的激素到牠們身上之後，

he found an even more surprising result—

出現了更令人驚訝的實驗結果：

the frogs began laying eggs.

牠們開始下蛋。

Normally, African clawed frogs only release eggs

非洲爪蟾一般來說只會在

when a male frog is nearby to fertilize them.

附近有公蛙和母蛙交配後才會下蛋，

But this ox hormone triggered their ovulation without the presence of a male.

但公牛的激素卻讓母非洲爪蟾在 沒有公蛙的情況下受到刺激開始排卵。

And this process gave the researchers an idea.

這讓科學家靈光一閃。

They knew there was a chemical similarity between the ox hormone

科學家知道公牛激素的 化學成分近似於

and a hormone found in the urine of pregnant people—

孕婦尿液裡帶有的激素，

a compound we know today as the chorionic gonadotropin hormone, or hCG.

如今稱作人絨毛膜促性腺激素（hCG）。

In pregnancy tests of the day,

當時驗孕

animals like mice and rabbits were injected with human urine

把測試者尿液注入老鼠和兔子體內， 看會不會讓牠們懷孕，

as a way of testing for the presence of hCG.

藉此鑑定尿液裡有沒有絨毛激素。

However, this required multiple days of injections,

但，光注入尿液的步驟就需要好幾天，

as well as killing and dissecting the animals

還要殺死並解剖這些實驗動物，

to see whether the hormone was present.

才能知道尿裡有沒有絨毛激素。

Because of these hurdles, the test was reserved for specific use cases,

因此這個驗孕測試只在特殊情況使用，

leaving most people waiting for visible signs to determine if they were pregnant.

使得大多數人必須等到 有明顯徵兆才知道自己懷孕了。

But these frogs changed everything.

但這隻青蛙改變了這樣的場面。

They responded to hCG in roughly 9 hours with no need for dissection.

母非洲爪蟾花 9 小時就對絨毛激素 產生反應，不需解剖就能見到結果，

And since their large ovaries constantly generate eggs,

且牠們龐大的子宮會定時製造卵細胞，

they could participate in numerous tests over their 15 to 30 year lifespan.

讓牠們在 15 到 30 年的壽命中 能被用於無數次的驗孕測試。

Better still, these frogs were abundant in their native habitat,

更棒的是，非洲爪蟾族群基數龐大，

making them easy to find, catch, and export.

所以科學家不用擔心缺貨。

Before long, tens of thousands of African clawed frogs

不久後，非洲爪蟾就被大量輸出

were being shipped to hospitals all over the world,

到世界各地的醫院，

making reliable pregnancy tests widely available for the first time.

這方便又可信的驗孕試劑 讓世界各地的人都受惠。

In the 1970s, the frogs would be superseded by chemical tests

1970 年，青蛙被化學試劑替代， 讓化學試劑直接測出絨毛激素的有無。

that detected hCG directly.

But by then their widespread presence in laboratories

但那時非洲爪蟾已經普及到

had made African clawed frogs the star of numerous studies.

實驗室能用非洲爪蟾來做大量實驗。

Their rapid development and ability to produce eggs in any season

非洲爪蟾的發育速度 和不分季節都能產卵的能力

made them invaluable models for developmental biology.

讓牠們成為發育生物學領域 無法取代的實驗動物。

African clawed frogs have even been part of biological studies

非洲爪蟾甚至參與了

aboard the Space Shuttle Endeavour.

奮進號太空梭的生物研究。

However, frogs can be slippery subjects.

然而，青蛙也容易「溜」走， 讓科學家很難管理。

More than a few of these amphibians have escaped their laboratory enclosures,

大量青蛙逃離實驗室的密閉區域，

and in many places,

而且在許多地方，

their ferocious appetite allowed them to outcompete native amphibians.

非洲爪蟾的驚人胃口 讓牠們成為當地入侵物種。

To make matters worse,

更糟的是，

they often carry a deadly fungus called chytrid,

牠們極可能帶有致命的真菌：壺菌，

which can cause an infection that lethally disrupts

兩棲類動物若感染到壺菌，

the delicate functioning of amphibian skin.

牠們敏感的皮膚會遭到致命地破壞。

In the 20th century, this fungal infection has devastated amphibian populations

在 20 世紀，壺菌的感染

沉重打擊全球兩棲類的數量，

around the globe,

causing the extinction of multiple frog species.

讓許多種不同青蛙面臨滅絕。

Because of all these concerns,

因為這些原因，

the African clawed frog is now classified as an invasive species,

現在非洲爪蟾被歸類為有害的入侵種，

and illegal in many regions.

許多地方立法禁止非洲爪蟾進入。

So in the end, like other pregnancy tests,

到頭來，就像驗孕測試結果，

the use of these frogs in scientific research

在科學研究裡導入非洲爪蟾的行為

has had both positive and negative results.

帶來許多「正面」和「負面」的結果。