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科学美国人60秒 SSS A Humble Fish with a Colorful Edge

时间:2017-03-06 07:09:00

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(单词翻译)

 

Hundreds of millions of years ago a humble1 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. 

Cichlids have some of the most incredible visual systems known. Humans have genes2 that code for three different types of visual pigments3, called opsins. Cichlids have seven.

"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."

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

"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." 

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

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 wavelength4 light, at the blue end of the spectrum5. But their South American counterparts live in the murky6 waters of the Amazon River basin, bathed mostly in reds and oranges. 

Escobar-Camacho analyzed7 DNA8 from three different Amazonian cichlids: the freshwater Angelfish, the Discus, and the Oscar, all of which are also popular in home aquariums9. 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. 

“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 wavelengths10 best.”

In other words, Amazonian cichlids were most sensitive to red and orange light, which makes sense because Amazonian rivers filter out most of the blues11 and greens. The results are in the journal Molecular12 Ecology. [Daniel Escobar-Camacho, Erica Ramos, Cesar Martins, & Karen L. Carleton. The opsin genes of Amazonian cichlids.]

The finding is consistent with an idea called the "sensitivity hypothesis," which holds that a color visual system evolves by adapting to the dominant13 wavelengths of light in the environment. In other words, what you get is what you see.  

—Jason G. Goldman


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1 humble ddjzU     
adj.谦卑的,恭顺的;地位低下的;v.降低,贬低
参考例句:
  • In my humble opinion,he will win the election.依我拙见,他将在选举中获胜。
  • Defeat and failure make people humble.挫折与失败会使人谦卑。
2 genes 01914f8eac35d7e14afa065217edd8c0     
n.基因( gene的名词复数 )
参考例句:
  • You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因,所以能够活得很长。 来自《简明英汉词典》
  • Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪
3 pigments 90c719a2ef7a786d9af119297e63a36f     
n.(粉状)颜料( pigment的名词复数 );天然色素
参考例句:
  • The Romans used natural pigments on their fabrics and walls. 古罗马人在织物和墙壁上使用天然颜料。 来自辞典例句
  • The original white lead pigments have oxidized and turned black. 最初的白色铅质颜料氧化后变成了黑色。 来自辞典例句
4 wavelength 8gHwn     
n.波长
参考例句:
  • The authorities were unable to jam this wavelength.当局无法干扰这一波长。
  • Radio One has broadcast on this wavelength for years.广播1台已经用这个波长广播多年了。
5 spectrum Trhy6     
n.谱,光谱,频谱;范围,幅度,系列
参考例句:
  • This is a kind of atomic spectrum.这是一种原子光谱。
  • We have known much of the constitution of the solar spectrum.关于太阳光谱的构成,我们已了解不少。
6 murky J1GyJ     
adj.黑暗的,朦胧的;adv.阴暗地,混浊地;n.阴暗;昏暗
参考例句:
  • She threw it into the river's murky depths.她把它扔进了混浊的河水深处。
  • She had a decidedly murky past.她的历史背景令人捉摸不透。
7 analyzed 483f1acae53789fbee273a644fdcda80     
v.分析( analyze的过去式和过去分词 );分解;解释;对…进行心理分析
参考例句:
  • The doctors analyzed the blood sample for anemia. 医生们分析了贫血的血样。 来自《简明英汉词典》
  • The young man did not analyze the process of his captivation and enrapturement, for love to him was a mystery and could not be analyzed. 这年轻人没有分析自己蛊惑著迷的过程,因为对他来说,爱是个不可分析的迷。 来自《简明英汉词典》
8 DNA 4u3z1l     
(缩)deoxyribonucleic acid 脱氧核糖核酸
参考例句:
  • DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。
  • Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。
9 aquariums 82747d9c1d5a367d4d227b28ed8cf5c6     
n.养鱼缸,水族馆( aquarium的名词复数 )
参考例句:
  • Biotope aquariums represent the natural environments of ornamental fish. 生态鱼缸表现出观赏鱼的自然生活环境。 来自互联网
  • There are aquariums in many cities in the world. 世界上好多城市有水族馆。 来自互联网
10 wavelengths 55c7c1db2849f4af018e7824d42c3ff2     
n.波长( wavelength的名词复数 );具有相同的/不同的思路;合拍;不合拍
参考例句:
  • I find him difficult to talk to—we're on completely different wavelengths. 我没法和他谈话,因为我们俩完全不对路。 来自《简明英汉词典》
  • Sunlight consists of different wavelengths of radiation. 阳光由几种不同波长的射线组成。 来自辞典例句
11 blues blues     
n.抑郁,沮丧;布鲁斯音乐
参考例句:
  • She was in the back of a smoky bar singing the blues.她在烟雾弥漫的酒吧深处唱着布鲁斯歌曲。
  • He was in the blues on account of his failure in business.他因事业失败而意志消沉。
12 molecular mE9xh     
adj.分子的;克分子的
参考例句:
  • The research will provide direct insight into molecular mechanisms.这项研究将使人能够直接地了解分子的机理。
  • For the pressure to become zero, molecular bombardment must cease.当压强趋近于零时,分子的碰撞就停止了。
13 dominant usAxG     
adj.支配的,统治的;占优势的;显性的;n.主因,要素,主要的人(或物);显性基因
参考例句:
  • The British were formerly dominant in India.英国人从前统治印度。
  • She was a dominant figure in the French film industry.她在法国电影界是个举足轻重的人物。

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