原文已被隐藏，你可用 快捷键 - 或点击 显示原文 按钮来查看原文
第一段
1 .Listen to part of a lecture in a biology class.
听一段生物课上的演讲
第二段
1 .Ways in which animals adapt to their environment are often quite ingenious actually.
动物适应环境的方式经常很独具匠心。
2 .And as an example of this, let me tell you about a fish, a group of fish known as the Notothenioids.
举个例子，有一类鱼叫做南极鱼亚目。
3 .There's over 90 known species of Notothenioids and they inhabit both shallow and very deep waters, mostly around Antarctica.
这类南极鱼亚目有超过90种，大多生活在南极洲附近的浅水和深水中。
4 .Many are fairly small, though the largest species can weigh up to 150 kilograms.
许多品种都非常小，但最大的品种重达150公斤。
第三段
1 .Notothenioids can be identified by their large eyes, which are covered by a thick insulating layer of clear tissue.
南极鱼亚目的特点是眼睛很大，同时眼睛被一层厚厚的、绝热的透明组织覆盖着。
2 .This tissue protects their eyes from freezing.
这层组织防止它们的眼睛上冻。
3 .Remember, the freezing point of ocean water, salt water, is lower than for fresh water, negative 1.9 degree Celsius.
还记得海水，也就是盐水，的凝固点要比淡水的低么：零下1.9摄氏度。
4 .So it can get a lot colder for fish in an ocean, say, than in a river or lake.
所以，对于海洋鱼来水，海水的温度其实要比河水和湖水低。
5 .So this means that the ocean waters around Antarctica are cold enough to freeze most types of fish, but Notothenioids don't freeze.
那么，这就意味着，南极洲附近的海水冷到足够让大多数种类的鱼结冻，但是南极鱼亚目则不会。
6 .In fact, they thrive.
实际上，它们却在繁荣壮大。
7 .They account for some 95% of all fish in the southern ocean, the ocean that surrounds Antarctica.
它们占南海，即南极洲周围的海，全部鱼群总数的95%。
第四段
1 .So, how unusual is that, to have a single family of fish dominating an entire ocean?
那么，这到底有多不寻常呢？
2 .I mean, think of... say, tropical or temperate marine environments, which have incredibly diverse fish populations.
单一的一类鱼占据了整个海洋，我是说，想想热带或恒温海域，那些地方的鱼群种类繁多。
3 .Coral reefs, for example, support over 4000 types of fish, along with sponges, crustaceans, and many other organisms.
例如，珊瑚礁养育着四千多种鱼，以及海绵、甲壳类和其他生物体
第五段
1 .So, exactly when and how did the Notothenioids come to dominate the southern ocean?
那么，南极鱼亚目又是如何占据了南海的呢？
第六段
1 .Well, around 30 million years ago, the waters around Antarctica were a lot warmer than they are today.
大概3000万年前，南极洲周围的水域要比今天暖许多。
2 .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 Antarctica waters.
当时，南极洲与南美洲是连着的，这就意味着北方的暖空气可以向南移动，使南极洲的水体变暖。
3 .Because the water around Antarctica then was relatively warm, it supported many types of fish.
因为当时南极洲附近的水体相对较暖，便有许多种类的鱼，
4 .And we know this from fossil evidence.
有化石样本为证。
第七段
1 .But the 90 or so species of Notothenioids that exist today didn't exist at all back then.
是今天存在的这90种南极鱼亚目在当时并不存在
2 .In fact, only one ancestral Notothenioid species existed.
。事实上，当时只有一种南极鱼亚目的祖先存在。
3 .But somewhere between 5 million and 14 million years ago, two major changes took place.
但在500万年前到1400万年前中间的某个时间点，发生两个重大的变化。
第八段
1 .First, what we call a chance mutation.
首先，发生了我们称之为机遇突变的现象，
2 .A tiny genetic change occurred in that one Notothenioid species.
那个当时存在的南极鱼亚目种类体内发生了一个小的基因变异。
3 .Its DNA allowed for the production of a special protein, a protein that prevents the fish from freezing.
这次基因变异生成了一种特殊的蛋白质，一种防止鱼冻结的蛋白质。
4 .The way this... this anti-freeze protein works is: it binds to any ice crystals that form inside the fish.
这种蛋白质的工作原理是它会将自己捆绑在鱼体内形成的任何冰晶，
5 .This binding action prevents the ice crystals from growing larger.
以防止冰晶变大。
6 .And this is what prevents Notothenioids from freezing.
这就是南极鱼亚目如何不会冻结的原理。
第九段
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.
那么，当时，南极鱼亚目生活的水域仍没有那么冰冷。所以，对于鱼的成活来说，蛋白质并没有起到什么作用。
2 .But this would change, because in the same period of geologic time there was a shift in the earth's continental plates.
但是这会变，因为在同一个地质时期内，地球的大陆板块进行了移动。
3 .Continental drift caused Antarctica to move apart from the landmass of South America and to drift into the Southern Polar Region.
大陆漂移让南极洲远离了南美洲大陆，而漂向了南部冷一些的区域。
4 .This resulted in a powerful water current encircling Antarctica, which prevented the Antarctic waters from mixing with warmer water.
这导致南极洲被强烈的水流包围，防止南极洲水体与暖一些的水体进行混合，
5 .So the southern ocean, isolated from that warm airflow from the north, cooled down drastically, to the kinds of sub-freezing temperatures we associate with it today.
所以南海被从北边的暖气流隔离开来，急剧降温，达到了我们今天这种零下温度。
第十段
1 .Now, most fish species couldn't survive in this frigid environment and they became extinct.
那么，大多数种类的鱼都不能在这种情况下生存，所以也便绝迹了，
2 .But that one Notothenioid species, with its unique ability to produce that anti-freeze protein, thrived.
但是唯独那一种南极鱼亚目，凭借着自己能生成防冻蛋白质的能力，大肆繁衍起来
3 .It had virtually the entire southern ocean to itself!
基本上整个南海都是它自己的
第十一段
1 .So? Well, there was little or no competition for food or space.
。所以，对食物和空间的竞争也就很少。
2 .You might think of it as... um... as a... a kind of ecological vacuum.
可以把它认为成是一种生态真空。
3 .And the Notothenioids exploited fully.
南极鱼亚目充分地利用了这个状态。
4 .The species migrated into different habitats throughout the southern ocean.
不同种类的南极鱼亚目迁徙到了南海的各个地域，种群数量也暴增，
5 .And its population increased dramatically, with various sub-populations migrating into different parts of the ocean.
并且分化成了许多次种群，生活在海洋的各个区域。
6 .Over time these sub-populations in all those different habitats... well, they developed very different physical traits.
随着时间的推进，这些生活在不同区域的次种群发展出了非常迥异的外在特征。
7 .They adapted to survive in their particular ecological niche, their... their position within a particular ecosystem.
它们为了存活，适应了自己特定的生态位，也就是在某个生态系统的位置。
第十二段
1 .We call this type of species diversification within a species "adaptive radiation".
我们把这种类型的物种分化叫做适应辐射。
2 .And what adaptive radiation is, is an evolutionary process by which a parent species rapidly undergoes changes resulting in various new species in order to fill multiple ecological niches.
适应辐射是指母物种为了适应众多的生态位，从而进行快速的变化的进化过程
3 .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，拿南极鱼亚目的例子来说，这个单一的物种开始在空栖息地大量繁衍，繁衍到进化出一系列新物种的程度：我们今天有的90种左右的南极鱼亚目。
4 .So let me switch to adaptive radiation with regard to another species that's also been very successful.
那么，让我来谈谈另一个成功进行了适应辐射的物种吧。