The cichlid, a small fish, has one of the most incredible visual systems known-which allows it to adapt to differently colored environments. Jason G. Goldman reports.

　　小小的丽鱼有着我们已知的一种最不可思议的视觉系统——这使它能够适应不同颜色的环境。杰森·戈尔德曼报道。

　　撰文/播音：杰森·戈尔德曼(Jason G. Goldman)

　　翻译：郭鑫鹏

　　审校：丁可含

　　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 cichlid, continue to swim the fresh waters of both Africa and South America.

　　几亿年前，一种小鱼畅游于冈瓦纳超大陆的湖泊和河流之中。冈瓦纳大陆最终分裂成我们现在所知的各个大陆。那种鱼的后代，现在被称为丽鱼，继续生活在非洲和南美洲的淡水中。

　　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.

　　慈鲷科鱼有着我们知道的一些最为奇妙的视觉系统。人类有三种不同类型视色素的基因，即视蛋白基因。而慈鲷科拥有七种。

　　“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.”

　　“但是慈鲷科包含了种类繁多的鱼类，有趣的是，它们这七种基因的表达组合也不尽相同。所以它们通常只表达三种，但是不同种类的丽鱼会表达这七种基因的任意三种。”

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

　　科利奇帕克马里兰大学生物学家丹尼尔·埃斯科瓦尔·卡马乔说。

　　“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.”

　　“所以举例来说，我们有编码蓝、绿、红的视蛋白基因……但是慈鲷科有着对紫外、蓝紫、蓝、蓝绿、绿、浅绿和红敏感的基因。”

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

　　但是选择上的压力只能保证这些基因中的一些是完整的。

　　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.

　　非洲慈鲷科鱼的视觉系统被充分研究过，它们在相当干净、平静，拥有足够光照的蓝色湖泊中进化而来。研究发现它们保留着能看到短波长光，即光谱蓝色段的基因。但是它们生活在亚马逊河流域的南美洲同伴们，看到的基本是红色和橙色。

　　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.

　　埃斯科瓦尔·卡马乔分析了三种不同亚马逊河慈鲷科鱼的DNA：淡水天使鱼、七彩神仙鱼(铁饼)，奥斯卡鱼，这些也常见于家庭鱼缸中。他发现每一品种至少完整地失去了七种视蛋白基因的一个，有些则失去了两个。但它们失去的都是不同的基因。

　　“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.”

　　“有趣的是他们视网膜上表达的基因使它们对长波长敏感。这与亚马逊河水的光照条件一致，因为亚马逊河水最能够传播长波长的光。”

　　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. [Daniel Escobar-Camacho, Erica Ramos, Cesar Martins, &Karen L. Carleton. The opsin genes of Amazonian cichlids.]

　　换句话说，亚马逊慈鲷科最敏感红、橙光，是因为亚马逊河流滤掉了大部分蓝光和绿光。该结果发表在期刊《分子生态学》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.

　　这项结果与被称为“敏感性假设”中的观点一致，该假设认为视觉颜色系统通过适应环境中占主要波长的光而进化。换而言之，你得到的就是你看到的。

　　-Jason G. Goldman