科学美国人60秒 SSS 一条小鱼（在线收听）

Hundreds of millions of years ago a humble fish swam in the lakes and rivers of the supercontinent Gondwana. Eventually Gondwana broke apart, becoming the continents we know today. And the descendants of that fish, now called cichlids, continue to swim the fresh waters of both Africa and South America.

几亿年前，一条小鱼儿游到古代冈瓦那大陆上的一片湖波和河流里。最后冈瓦那大陆断裂，变成了今天的大陆大洲。而那条鱼的后代，现在被称为棘鳍类热带淡水鱼，继续的在非洲和南美洲上的淡水中畅游着。

Cichlids have some of the most incredible visual systems known. Humans have genes that code for three different types of visual pigments, called opsins. Cichlids have seven.

丽鱼拥有一些最不可思议的视觉系统。人类有编码三种不同视觉色素蛋白的基因，称为视蛋白. 丽鱼有七种。

"But what is interesting within cichlids, which is this group of very diverse fishes, is that they can express different sets of these seven genes. So they only express three typically, but different species express different groups of these seven genes."

这种鱼类中有很多不同品种，有趣的是，每种鱼的亚种会分别表达这7种基因中的不同的组合。所以一般也只有三种视蛋白被表达，但是这种鱼不同的品种会分别表达这7种基因中的不同的三种。

Biologist Daniel Escobar-Camacho, from the University of Maryland in College Park.

Daniel Escobar-Camacho，来自于马里兰大学的生物学家。

"So for example, we have opsin genes that code for the blue, green, and red opsin…whereas cichlids have genes that are sensitive to UV, violet, blue, blue-green, green, light green, and red."

所以比如说，我们有编码蓝色绿色红色视蛋白的视蛋白基因，可是丽鱼的视蛋白基因里有编码对紫外线，紫色，蓝色，蓝绿，绿色，浅绿和红色光敏感的视蛋白基因。

But selection pressure has kept only some of those genes intact.

但是自然选择的压力使得最后只有部分基因被表达。

African cichlids, whose visual systems are well studied, evolved in fairly clear, calm, blue lakes with plenty of sunlight. And it was known that they’ve maintained the genes for seeing short wavelength light, at the blue end of the spectrum. But their South American counterparts live in the murky waters of the Amazon River basin, bathed mostly in reds and oranges.

非洲的丽鱼，人类已经仔细研究过了它们的视觉系统。它们生存进化的环境是清澈，安静的蓝色湖面，拥有充足的阳光。而据说它们的视蛋白基因表达出的蛋白是识别短波长光线的光，可见光谱中偏蓝光。但是它们在南美洲的同伴们，生长在昏暗潮湿的亚马逊河流域，大部分时间沐浴的是红色和橙色的光。

Escobar-Camacho analyzed DNA from three different Amazonian cichlids: the freshwater Angelfish, the Discus, and the Oscar, all of which are also popular in home aquariums. He discovered that each species has completely lost at least one of the seven opsin genes, and some have even lost two. But they've each lost different genes.

Escobar-Camacho分析了三种不同亚种的亚马逊丽鱼的DNA：淡水蓝刺蝶鱼，七彩神仙鱼和奥斯卡鱼，都是在家庭水族箱中很常见的品种。结果发现，每种都完全丢失了上述7种视蛋白基因中的一种，有些甚至丢失两种。但是它们丢失的基因种类都互不相同。

“What is interesting is that they are expressing genes in the retina that allow them to be long wavelength-sensitive. And this is in concordance with the light environment in Amazon waters, because Amazon waters transmit long wavelengths best.”

有趣的是它们在视网膜中有相关基因表达，可以帮助识别长波长的光。这与生活在亚马逊流域中的光环境相一致，因为亚马逊流域传播的大多是长波长光。

In other words, Amazonian cichlids were most sensitive to red and orange light, which makes sense because Amazonian rivers filter out most of the blues and greens. The results are in the journal Molecular Ecology.

换句话说，亚马逊丽鱼对红光和橙色光线最敏感，因为亚马逊河过滤掉了大部分蓝光和绿光，所以这种进化很有意义。该研究结果已发表在《分子生态学》杂志上。

The finding is consistent with an idea called the "sensitivity hypothesis," which holds that a color visual system evolves by adapting to the dominant wavelengths of light in the environment. In other words, what you get is what you see.

该研究的结果与一个名为“敏感度假说”的观点相符合，这个观点认为，对一种颜色的视觉系统的进化是由于适应了其所在环境中占主要的光的波长。这么说吧，所见即所得。