These animals are also plants … wait, what? - Luka Seamus Wright

翻译人员: Alex Chang 校对人员: Yuwei Wu

Take a good look at this slug.

好好看看这条鼻涕虫。

No, not that— that’s a leaf.

不，不是那个—— 那只是片叶子。

This slug.

这只。

There we go.

让我们仔细看看。

Elysia chlorotica may not look like much—

绿叶海天牛可能看起来不那么——

okay, it looks like a bright green leaf—

好吧，他确实看起来 像一片翠绿的叶子——

but it’s one of the most extraordinary creatures around.

但它是这片环境中 最不寻常的生物之一。

Living in salt marshes along the east coast of North America,

生活在北美东海岸的盐沼中，

it can go about a year without eating.

它可以一年不吃东西。

During that time, it lives like a plant.

在此期间，它像植物一样生活。

Generally speaking, animals are what are called heterotrophs,

一般来说，动物是“异养生物”，

meaning they can’t produce their own food— they’re consumers of other life.

意味着它不能自己生产食物， 而是其他生命体的“消费者”。

Plants, meanwhile, are autotrophs, or producers:

植物，与此同时，作为 “自养生物”，抑或是“生产者”：

they can synthesize their own fuel from sunlight, CO2,

它们可以通过合成阳光， 二氧化碳为自己提供能量，

and other inorganic compounds.

及其他无机化合物。

Plants do this by using organelles called chloroplasts,

植物通过“叶绿体”的细胞 体实现上述功能，

which give them their bright colors

”叶绿体“赋予它们鲜亮的颜色，

and convert sunlight into food through photosynthesis.

并通过光合作用将阳光转化为食物。

Elysia is what’s called a mixotroph:

绿叶海天牛是一种混合营养生物

it can both consume food, like animals,

它可以像动物一样消费食物，

and produce its own through photosynthesis, like plants.

也可以通过光合作用自己制造食物。

In fact, Elysia steals its ability to photosynthesize

实际上，绿叶海天牛的 光合作用的能力是”偷“的

from the algae it eats by piercing the algal cells

它通过进食藻类，并咬破藻类细胞

with specialized pointy teeth, called radula.

用它被成为”齿舌“，特别的尖牙。

It sucks the cell empty and digests most of its contents,

它将细胞吸空， 并消耗其大部分物质，

but the chloroplasts remain intact.

留下”叶绿体“完好无损。

They’re incorporated into the epithelial cells lining Elysia’s digestive system

它们被整合到绿叶海天牛 消化系统的上皮细胞中

that branches throughout its flat body.

并广泛分布在它扁平的身体上。

This makes the slug look even more leaflike,

这让它看起来更像叶子了，

providing camouflage as well as food.

不仅提供食物，还能作为伪装。

As incredible as this adaptation is,

如此令人难以置信的适应性，

there are more than 70 species of slug that steal chloroplasts from their food.

竟然有多达 70 多种鼻涕虫 从食物中窃取叶绿体。

What makes Elysia and a few closely related species

让绿叶海天牛及少数相近种群，

in the Mediterranean and Pacific unique

成为地中海和太平洋中 独一无二的存在

is how long they can hold onto chloroplasts—

是它们能够将 叶绿体保存的足够久——

most other slugs keep them for a few weeks at most.

其他大部分的鼻涕虫 最多能保存几周。

This longevity seems to be due to the survival abilities

保存的长度取决于 以下两者的生存能力

of both plastids and slugs.

即植物细胞的质体和鼻涕虫本身。

Specifically, the chloroplasts of certain algae

具体来说，某些特定藻类的叶绿体

can repair their own light-harvesting systems,

能够自我修复阳光吸收系统，

while most chloroplasts are thought to rely on their host cell

而大多数叶绿体 则依赖于它们的宿主细胞

and its genes for repairs.

及其修复基因。

This makes the chloroplasts able to sustain themselves

这使得叶绿体能够维持自身存活

for longer inside the slug.

在鼻涕虫体内更长的时间。

Meanwhile, the slug adjusts its gene expression

与此同时，鼻涕虫通过 调整自身的基因表达

to improve its relationship with the chloroplasts

改进与叶绿体的相互作用

and removes damaged plastids

并去除受损的质体。

to avoid accumulation of potentially damaging chemicals.

从而避免具有潜在 破坏性化合物的累积。

Though few species can steal organelles from another species’ cell,

尽管少数物种能够从 其他物种细胞中窃取细胞体

these slugs are far from alone in getting an assist from plants.

能从植物获得帮助这点来看， 鼻涕虫并不孤单。

Organisms as diverse as corals,

珊瑚有着丰富的生物多样性，

giant clams and sponges have symbiotic algae living inside their cells,

巨蚌和海绵与体内的藻类共生，

supplying them with organic compounds through photosynthesis.

通过光合作用 为它们提供有机化合物。

In turn, they supply their little helpers with shelter and inorganic compounds.

作为回报，它们为这些小助手们 提供庇护所和无机化合物。

Some of these mixotrophs even transmit the algae to their offspring.

其中有些混合营养生物 甚至将藻类传给自己的后代。

Without the aid of these algae,

没有这些藻类的帮助，

filter-feeding corals, clams, and sponges would not gain enough nutrition

滤食性珊瑚、蚌壳和海绵 无法获得充足的营养

in the nutrient-poor tropical ocean,

在营养匮乏的热带海洋中，

and the dazzling coral reefs they build simply would not exist.

令人瞠目结舌的珊瑚 礁根本无法建成。

Mixotrophy even cuts both ways:

混合营养生物甚至可以 向两个方向转变：

an alga called Tripos furca can consume several microscopic animals a day,

一种叫骨叉角藻的藻类 每天可以吃几只微型动物，

allowing it to survive in darkness for weeks.

帮助它在黑暗中存活数周。

Tripos is in turn eaten by other mixotrophic algae,

角藻又被其他混合营养藻类吞食，

providing frequent opportunity for exchange of organelles

为交换细胞器提供充分的可能

such as chloroplasts.

比如叶绿体。

This seems to allow some algae to survive in parts of the dark ocean

这似乎帮助藻类 在部分黑暗的海洋中生存

such as the Mariana Trench,

比如马里亚纳海沟，

which plants otherwise wouldn't be able to inhabit.

植物根本无法在那里生存。

The processes by which Elysia becomes photosynthetic

绿叶海天牛进行光合作用的能力

and Tripos switches between feeding modes

以及角藻在两种饮食模式中切换

are reminiscent of what scientists believe led to the origin of all plants.

被科学家认为 是所有植物起源的标志。

Single-celled animals preyed on cyanobacteria.

蓝藻捕食单细胞动物。

Some of these tiny plants were not digested and lived on in the animal cells,

这些微小植物并无法 消化和吸收这些动物细胞，

eventually giving rise to chloroplasts.

最终形成了叶绿体。

But these first eukaryotic plants were soon consumed by other animals,

但这些最早的真核植物 很快就被其他动物吃掉了，

which hijacked the precious chloroplast, just like Elysia.

并被劫持了珍贵的叶绿体， 就像绿叶海天牛一样。

And following the example of eating and being eaten,

吃与被吃的情况不断重复，

we’ve seen in the case of Tripos,

正如我们在角藻的案例中看到的，

this chloroplast heist happened up to three times,

叶绿体在这个过程中被劫持了三次，

giving rise to plastids with four membranes

产生了具有四层膜的质体

and the ocean’s most productive plants and forests.

成为海洋中最富 生产力的植物和森林。