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第1段
1 .<-NARRATOR:-> Listen to part of a lecture in a biology class.
旁白：听一段生物学课程。
第2段
1 .<-FEMALE PROFESSOR:-> [responding to a student’s comment]…Ways in which animals adapt to their environment are often quite ingenious, actually.
教授：其实，动物适应所处环境的方式通常都是非常具有独创性的。
2 .And, as an example of this, lemme tell you about a fish … a-a group of fish known as the notothenioids.
举个例子，让我给你们讲讲一种鱼吧，这类鱼称为南极鱼类。
第3段
1 .There's over 90 known species of notothenioids, and they inhabit both shallow and very deep waters-mostly around Antarctica.
南极鱼类一共超过90种，它们栖息在浅水和深水域，主要在南极洲附近。
2 .Many are fairly small, though the largest species can weigh up to 150 kilograms.
其中很多南极鱼都相当小，尽管最大的鱼体重能达到150千克。
3 .Notothenioids can be identified by their large eyes, which are covered by a thick, insulating layer of clear tissue.
南极鱼可通过它们的大眼睛被辨认出来，这些眼睛被一层厚厚的，绝缘的透明组织所覆盖。
4 .This tissue protects their eyes from freezing.
这些组织保护它们的眼睛不被冻伤。
5 .Remember, the freezing point of ocean water-saltwater-is lower than for freshwater-negative 1.9 [one-point-nine]degrees Celsius … so it can get a lot colder for fish in an ocean, say, than in a river or lake.
记住，海水的结冰点，即盐水，是比淡水低的，零下1.9摄氏度。所以，对鱼来说，在海里比在河里或湖里冷多了。
第4段
1 .So … this means that the ocean waters around Antarctica are cold enough to freeze most types of fish. But notothenioids don't freeze. In fact, they thrive.
这就意味着，南极洲附近的海水非常冷，足以冻住大多数鱼类，但南极鱼则不会。事实上，它们非常兴旺。
2 .They account for some 95 percent of all fish in the Southern Ocean-the ocean that surrounds Antarctica.
南极鱼在南部海域鱼类里占几乎95%，即南极洲周围海域。
第5段
1 .So, how unusual is that …to have a single family of fish dominating an entire ocean?
这多么不寻常啊？一种鱼类主宰了整片海域。
2 .I mean, think of, say, tropical or temperate marine environments,which have incredibly diverse fish populations.
我是指，想想热带或温带的海洋环境，那儿的鱼非常多样。
3 .Coral reefs, for example, support over 4,000 types of fish,along with sponges … crustaceans … and many other organisms.
比如说珊瑚礁，就养活了超过4000种鱼，还有别的海绵生物、甲壳类生物和其它生物。
第6段
1 .So, exactly when-and how-did the notothenioids come to dominate the Southern Ocean?
那么，到底是什么时候，以及通过什么方式，南极鱼类统治了南方海域呢？
2 .Well, around 30 million years ago, the waters around Antarctica were a lot warmer than they are today.
在大约三千万年前，南极洲周围水域比现在暖和多了。
3 .Um … at that time, Antarctica was connected to South America, which means that warm air, from the north, could flow southward and heat up the Antarctic waters.
那时候，南极洲连着南美洲，也就是说，从北方来的暖空气可以一直流向南方，加热南极洲水域。
4 .Because the water around Antarctica then was relatively warm, it supported many types of fish, and we know this from fossil evidence.
因为那时候南极洲附近水域相对暖和，也就给很多鱼类提供了生存环境，我们是从化石证据中知道这些的。
5 .But the 90 or so species of notothenioids that exist today didn't exist at all back then ….
但现在存在的90多种的南极鱼类在那时候还没出现呢。
6 .In fact, only one ancestral notothenioid species existed.
实际上，（那时候）只有一种古老的南极鱼。
第7段
1 .But somewhere between five million and fourteen million years ago,two major changes took place.
但在一千四百万年前到五百万年前之间，发生了两个重大变化。
2 .First, what we call a chance mutation-a tiny genetic change-occurred in that one notothenioid species.
第一个是我们称为的偶然突变，一个微小的基因突变发生在那种古老的南极鱼中。
3 .Its DNA allowed for the production of a special protein,a protein that prevents the fish from freezing.
它的基因产生了一种特殊的蛋白质，这种蛋白质能保护南极鱼不被冻住。
4 .The way this-this antifreeze protein-works is:it binds to any ice crystals that form inside the fish.
这种抗冻蛋白工作的原理是：它会附在鱼类体内的每一个冰晶上。
5 .This binding action prevents the ice crystals from growing larger … and this is what prevents notothenioids from freezing.
这种粘附能防止冰晶变大，这就能保护南极鱼不受冻了。
第8段
1 .Now, at that time, the waters the notothenioids inhabited were still not freezing cold. So the protein didn't really make a difference, as far as the fish's survival.
在那时候，南极鱼所在水域还没有那么冷，所以这种蛋白对于鱼类生存来说，并没有起很大作用。
2 .But this would change because, in the same period of geologic time, there was a shift in the Earth's continental plates; continental drift caused Antarctica to move apart from the landmass of South America and to drift into the southern polar region.
但这很快就会改变，因为在同一地质时期，地球的大陆板块发生了变化，大陆漂移导致南极洲从南美大陆中分离出来，漂流到南极区域。
3 .This resulted in a powerful water current encircling Antarctica,which prevented the Antarctic waters from mixing with warmer water… so the Southern Ocean-isolated from that warm airflow from the north-cooled down-drastically-to the kinds of subfreezing temperatures we associate with it today.
这导致南极洲被一股强水流环绕，阻止了南极洲水域和温度更高的水融合。所以，南部海域与来自北方的暖气流隔绝了，大幅度降温，达到了低于结冰点的温度，也就是今天的温度。
第9段
1 .Now, most fish species couldn't survive in this frigid environment,and they became extinct.
大部分鱼类在如此寒冷的环境下都无法生存，很快灭绝了。
2 .But that one notothenioid species, with its unique ability to produce that antifreeze protein,thrived. It had virtually the entire Southern Ocean to itself- so … well, there was little or no competition for food or space.
但那种南极鱼，有了独一无二的制造抗冻蛋白的能力，茁壮成长。基本上整个南部海域都是它的了！所以...那儿几乎没有关于食物和生存空间竞争。
3 .You might think of it as, um …[searching for a metaphor] as a—a kind of … an ecological vacuum; … and the notothenioids exploited it fully.
你大概能把它当成……一种生态真空。南极鱼充分利用了这一点。
4 .The species migrated into different habitats throughout the Southern Ocean,and its population increased dramatically, with various subpopulations migrating into different parts of the ocean.
这种鱼迁徙到不同的栖息地，遍布整个南部海域。鱼类数量大幅增加，发展出很多不同的亚种，迁徙到海洋的不同区域。
第10段
1 .Over time, these subpopulations, in all those different habitats … well, they developed very different physical traits; they adapted to survive in their particular ecological niche—[explaining the term] their … their position within a particular ecosystem.
久而久之，这些在不同栖息地的亚种……它们发展出了差异很大的生理特性。它们适应了在自己特定的生态位生存，即它们……它们在某个特定生态系统中的位置。
2 .We call this type of species diversification within a species adaptive radiation.
我们称这种种类物种多样化为“适应性辐射”。
3 .And what adaptive radiation is: is [slowly, stating a definition] an evolutionary process by which a parent species rapidly undergoes changes resulting in various new species, in order to fill multiple ecological niches.
适应性辐射是什么呢：它是一种进化过程，母种迅速经历了许多改变，导致了新物种出现，来填补更多的生态位。
4 .So, in the case of the notothenioids, that single species started colonizing empty habitats to such an extent that it evolved into a broad range of new species-the 90 or so notothenioid species that we have today.
所以，在南极鱼的例子中，单一物种开始在空旷的栖息地大量繁殖，以至于它进化出了形形色色的新物种—也就是我们今天拥有的90多种南极鱼。
5 .[slight pause] So, lemme switch to adaptive radiation with regard to another species that’s also been very successful ….
让我（把话题）切换到另一个非常成功的物种，它也有适应性辐射。