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The reason that Vibrio fischeri is doing that comes from the biology.
費氏弧菌的發光現象來自生物學上的原因。
Again, another plug for the animals in the ocean, Vibrio fischeri lives in this squid.
接下來，我們再來看一個海洋生物：費式弧菌寄生在這種烏賊的體內。
What you are looking at is the Hawaiian Bobtail Squid, and it's been turned on its back,
你們現在看到的是夏威夷截尾烏賊，這是它的腹側，
and what I hope you can see are these two glowing lobes and these house the Vibrio fischeri cells,
我希望你們看得到，那兩個發著光的葉狀突起，這里是費式弧菌的寄生之處，
they live in there, at high cell number that molecule is there, and they're making light.
他們居住在這里面。他們分泌的小分子也在這里面，所以它們能夠發光。
The reason the squid is willing to put up with these shenanigans is because it wants that light.
這種烏賊之所以愿意接受它們在里面胡作非為，是因為它需要這些亮光。
The way that this symbiosis works is that this little squid lives just off the coast of Hawaii, just in sort of shallow knee-deep water.
這種共存行為的建立基礎，是因為這種小烏賊生活在夏威夷的海岸，大概只有膝蓋一般深的水里。
The squid is nocturnal, so during the day it buries itself in the sand and sleeps, but then at night it has to come out to hunt.
這種烏賊是夜行性的，因此在白天它們藏在沙子里睡覺，但是到了晚上，它們必須出來獵食。
On bright nights when there is lots of starlight or moonlight that light can penetrate the depth of the water the squid lives in,
在有著許多星光與月光的明亮夜晚，這些光線可以照透烏賊所生活的地方，
since it's just in those couple feet of water.
因為這里的海水只有數尺深而已。
What the squid has developed is a shutter that can open and close over this specialized light organ housing the bacteria.
這種烏賊演化出了一種活葉瓣，可以打開或關閉細菌所寄生的發光器官。
Then it has detectors on its back so it can sense how much starlight or moonlight is hitting its back.
這種烏賊背上有一些感光裝置，可以測量有多少月光或星光照在它背上，
And it opens and closes the shutter so the amount of light coming out of the bottom -- which is made by the bacterium
然后調節它的活葉瓣，使從它腹部所放出的光--細菌產生的光，
exactly matches how much light hits the squid's back, so the squid doesn't make a shadow.
完全符合照射在烏賊背上的光強度。因此這烏賊就不會產生任何影子。
It actually uses the light from the bacteria to counter-illuminate itself in an anti-predation device
它們使用來自細菌的光，不斷調節光線，就像穿上隱身衣，
so predators can't see its shadow, calculate its trajectory, and eat it.
使獵食者無法看見它的陰影，計算它的動向，然后吃了它。
This is like the stealth bomber of the ocean.
就像是大海中的隱形轟炸機一般。
