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The reason that Vibrio fischeri is doing that comes from the biology.
费氏弧菌的发光现象来自生物学上的原因。
Again, another plug for the animals in the ocean, Vibrio fischeri lives in this squid.
接下来，我们再来看一个海洋生物：费式弧菌寄生在这种乌贼的体内。
What you are looking at is the Hawaiian Bobtail Squid, and it's been turned on its back,
你们现在看到的是夏威夷截尾乌贼，这是它的腹侧，
and what I hope you can see are these two glowing lobes and these house the Vibrio fischeri cells,
我希望你们看得到，那两个发着光的叶状突起，这里是费式弧菌的寄生之处，
they live in there, at high cell number that molecule is there, and they're making light.
他们居住在这里面。他们分泌的小分子也在这里面，所以它们能够发光。
The reason the squid is willing to put up with these shenanigans is because it wants that light.
这种乌贼之所以愿意接受它们在里面胡作非为，是因为它需要这些亮光。
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.
这种共存行为的建立基础，是因为这种小乌贼生活在夏威夷的海岸，大概只有膝盖一般深的水里。
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.
这种乌贼是夜行性的，因此在白天它们藏在沙子里睡觉，但是到了晚上，它们必须出来猎食。
On bright nights when there is lots of starlight or moonlight that light can penetrate the depth of the water the squid lives in,
在有着许多星光与月光的明亮夜晚，这些光线可以照透乌贼所生活的地方，
since it's just in those couple feet of water.
因为这里的海水只有数尺深而已。
What the squid has developed is a shutter that can open and close over this specialized light organ housing the bacteria.
这种乌贼演化出了一种活叶瓣，可以打开或关闭细菌所寄生的发光器官。
Then it has detectors on its back so it can sense how much starlight or moonlight is hitting its back.
这种乌贼背上有一些感光装置，可以测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
然后调节它的活叶瓣，使从它腹部所放出的光--细菌产生的光，
exactly matches how much light hits the squid's back, so the squid doesn't make a shadow.
完全符合照射在乌贼背上的光强度。因此这乌贼就不会产生任何影子。
It actually uses the light from the bacteria to counter-illuminate itself in an anti-predation device
它们使用来自细菌的光，不断调节光线，就像穿上隐身衣，
so predators can't see its shadow, calculate its trajectory, and eat it.
使猎食者无法看见它的阴影，计算它的动向，然后吃了它。
This is like the stealth bomber of the ocean.
就像是大海中的隐形轰炸机一般。
