How we can detect pretty much anything - Hélène Morlon and Anna Papadopoulou

譯者: Lilian Chiu 審譯者: Amanda Zhu

For years, scientists have been staking out this remote forest in Montana

多年來，科學家一直在監視 蒙大拿州這片偏遠的森林，

for an animal that’s notoriously tricky to find.

為了找一種出了名難找的動物。

Camera traps haven’t offered definitive evidence,

相機陷阱還無法提供決定性的證據，

and even experts can't identify its tracks with certainty.

就連專家也無法明確地辨別牠的足跡。

But within the past decades,

但過去數十年來，

researchers have developed methods that can detect even the most elusive species.

研究者已經開發出一些方法， 能偵測到行蹤最難以捉摸的物種。

And so, in 2018, these scientists took a sample from some conspicuous snow tracks.

於是，2018 年，

這些科學家從留著 明顯足跡的雪地上取樣。

Lab tests showed conclusive results:

實驗室的檢測顯示了確鑿的結果：

the Canada lynx was indeed present in the area.

加拿大猞猁的確在這個地區出沒。

Without seeing the cat, scientists had proof it was there

科學家不用看到這種貓， 就能證明牠曾經出現，

because of environmental DNA or eDNA.

靠的就是環境 DNA，或稱 eDNA。

Using a technique called DNA metabarcoding,

使用 DNA 高通量分子條碼技術，

researchers can take a sample from the environment

研究者可以從環境取得樣本，

and learn which organisms are in it or have recently passed through it.

找出哪些有機體在那裡

或最近曾經過此處。

The world is covered in DNA.

世界被 DNA 所覆蓋。 我們周遭都是 DNA——

It’s all around us—

on the ground, at the bottom of the ocean, and up in the clouds.

地面上、海底，以及雲朵上。

Multicellular organisms are constantly shedding cells.

多細胞有機體經常會有細胞脫落。

But until recently, eDNA wasn’t very useful to us.

但在不久前，eDNA 對我們還不是很有用。

Traditional scientific techniques couldn’t parse environmental samples

如果環境樣本中混合了 多種物種的基因物質，

containing mixed genetic material from multiple species.

傳統的科學技術就無法解析，

But DNA metabarcoding can.

但 DNA 高通量分子條碼可以。

DNA begins to degrade once it’s exposed to the environment.

DNA 暴露在環境當中就會開始降解。

In the ocean, for example, it may only persist for a few days.

舉例來說，在海洋中， DNA 只能存留幾天。

So in many contexts, eDNA is useful for telling us about the recent past.

所以在許多情況下，

eDNA 可以告訴我們不久前的過去。

The process of DNA metabarcoding starts with an environmental sample

DNA 高分子通量條碼的程序 要從環境採樣開始，

like a core of soil, a vial of water, some feces, an insect trap,

比如一把土壤、一小瓶水、

一些排泄物、一個昆蟲陷阱，

or even the blood from leeches’ stomachs.

甚至水蛭胃部裡的血。

Researchers then sift out everything aside from DNA by blending the sample up

接著，研究者會把 不是 DNA 的東西通通篩掉，

做法是把樣本均勻混合，

and using enzymes that break down cellular proteins and release DNA,

並使用酵素來分解細胞蛋白質，

釋放出純化的 DNA，

which they purify.

The result is a “soup” of all the DNA in the sample.

最後得到的是含有樣本中 所有 DNA 的液體。

Scientists then apply the polymerase chain reaction or PCR,

接著，科學家再應用 聚合酶連鎖反應，或稱 PCR，

which uses artificial DNA strands called universal primers.

用的是一種叫做通用引子的 人工 DNA 鏈，

These primers bind to DNA sequences that are similar across species,

所有物種都有相似的 DNA 片段， 通用引子會和這些片段結合，

then amplify genetic barcodes that are species-specific.

並大量複製各物種特有的片段， 得到放大的基因條碼。

High-throughput sequencing then reads millions of these DNA fragments,

高通量定序接著就會同時讀取 這數百萬個 DNA 片段。

simultaneously.

And finally, researchers compare them to reference databases

最後，研究者將它們 和參考資料庫做比對，

and identify how many and which species are present—

辨識出有多少種物種出現 以及是哪些物種，

or if they’ve found entirely new ones.

或者是否發現了全新的物種。

This method has led to the discovery of tens of thousands of species

靠著這種方法，在過去十年間

有數萬種物種被發現。

over the past decade.

While metabarcoding can detect elusive animals like the Canada lynx,

高通量分子條碼 能偵測到很難找的動物，

如加拿大猞猁，

it can also help scientists identify invasive species.

也能協助科學家找出入侵物種。

In Yosemite, researchers used eDNA to track and remove invasive bullfrogs.

在優勝美地國家公園，

研究者用 eDNA 來追蹤和除掉入侵的牛蛙。

Once no trace of these amphibians remained,

一旦不再有這些兩棲動物的蹤跡，

they reintroduced a threatened native species, California red-legged frogs,

他們才重新引入 一種受威脅的原生物種，

加州紅腿蛙，

which had disappeared from the area some 50 years prior.

大約五十年前這種紅腿蛙 就從該地區消失。

Likewise, DNA metabarcoding can be used to monitor biodiversity.

同樣地，DNA 高通量分子條碼 可以用來監控生物多樣性。

For example, using traditional approaches,

比如，若用傳統方法，

categorizing all of the insects in a hectare of rainforest can take decades.

將一公頃雨林中所有的昆蟲做分類

可能要花上數十年。

But DNA from insect traps could yield these results in just a few months.

但若用從昆蟲陷阱取得的 DNA， 只要幾個月就能得到分類結果。

One study compared insects from adjacent forest and plantation sites

有一項研究比較了中國雲南省中

within China’s Yunnan province.

相鄰的森林與造林地裡的昆蟲。

It quickly found that not only were plantations less diverse,

該研究很快就發現， 不僅造林地的多樣性比較低，

but deforestation affected insect groups unequally.

砍伐森林對於 各種昆蟲的影響也不相同。

Grasshoppers thrived in cleared areas while specialist forest beetles declined.

在樹木被砍光的地方有很多蚱蜢，

森林甲蟲卻減少了。

Using eDNA, scientists are able to investigate

靠著 eDNA，科學家便能研究

complex ecosystem interactions.

複雜的生態系統交互作用。

Tracking thousands of insects as they visit flowers is impossible.

要在數千種昆蟲採花蜜時 追蹤牠們是不可能的。

Instead, researchers can study the DNA left on flowers and insects

反之，研究者可以研究 留在花上和昆蟲身上的 DNA，

to map pollination networks.

以繪出授粉網路圖。

Before these techniques were available, we didn’t really know how much pollination

在這些技術出現之前，

我們不知道有多少授粉發生在夜間，

was happening at night because we couldn’t observe it.

因為我們無法觀察。

Now scientists understand that moths are important nocturnal pollinators.

現在，科學家知道蛾類 是重要的夜間傳粉昆蟲。

eDNA can even tell stories of long extinct species.

eDNA 甚至可以告訴我們 絕種已久的物種的故事。

Cold, dry, and low oxygen conditions are perfect for preserving genetic material.

寒冷、乾燥、低氧的條件

很適合保存基因物質，

By digging deep into the Arctic permafrost,

研究者在挖掘 北極永久凍土層的深處時，

researchers found 50,000 year old DNA,

發現了五萬年前的 DNA，

which they matched to the nutrient-rich plants

這 DNA 與長毛象胃部裡找到的

found in the stomachs of woolly mammoths.

營養豐富的植物吻合。

With eDNA, they also found that less nutritious grasses

靠著 eDNA，他們也發現 比較沒有營養的草

colonized the Arctic steppe during the last ice age,

在上一次冰河時期， 曾經生長在北極大草原上，

potentially contributing to the mammoth decline.

這可能是長毛象數量減少的原因。

As we face another period of climate change—

現在我們正面臨 另一個氣候變遷時期

this time due to human activities—

——這次是人類活動造成的——

understanding our planet’s rapidly shifting biodiversity

了解地球變化快速的生物多樣性

will be crucial to protecting it.

對於保護地球來說是很重要的。

Fortunately, eDNA and metabarcoding

幸而我們有 eDNA 和高通量分子條碼

give us the tools to document rapid change in real time.

來即時記錄快速的改變。