2021年经济学人 性选择和物种形成(2)

Genetic¹ sequencing shows just how similar these species are. Only 12 of their genes² differ—less than 0.1% of their genomes. Intriguingly³, one of the 12 is part of one of the sex chromosomes⁴, hinting at a role for sexual selection. Another three of them play a role in the colouration of male plumage, which is also suggestive. For, although the species are of similar sizes and shapes, adult male tawny-bellied seedeaters, as their name implies, have brownish-orange chests, while male Ibera seedeaters have black throats and sandy-coloured bodies. Their songs are distinct, too. They use the same range of frequencies, but different syllables⁵.

基因测序显示了这些物种的极度相似性。他们只有12个基因不同——不到基因组的0.1%。有趣的是，这12条染色体中有一条是其中一条性染色体的一部分，这暗示了性选择的作用。另外三条对雄性羽毛的颜色也有影响，这也很有启发性。因为，尽管这两个物种的大小和形状相似，但成年雄性茶腹食籽雀(如它们的名字所示)的腹部是茶色的，胸部是橙色的，而雄性伊比利亚食籽雀的喉咙是黑色的，身体是沙色的。此外它们的鸣啭也截然不同，使用的频率范围是相同的，但音节不同。

First, Ms Turbeck and her colleagues established that females of both species did, indeed, regularly select the right mates. Observation of pairs suggested so, and genetic testing of young (needed because more than half the females under study mated with extra males in addition to their long-term partners) did not find any exceptions, either. That done, they looked at males' abilities to distinguish conspecific rivals from heterospecific neutrals. During the 2019 breeding season they mounted decoy males in the territories of 40 male tawny-bellied seedeaters and 36 male Ibera seedeaters. They then monitored the residents' responses when a female was around.

首先，图贝克女士和她的同事证实了一点，即这两个物种的雌性确实会定期选择合适的配偶，对配偶的观察也证实了这一点，而且对年轻配偶进行的基因检测(需要做是因为在研究中有超过一半的雌性除了长期伴侣外还与其他雄性交配)也没有发现任何例外。研究完成后他们观察了雄性区分同种对手和异种中性对手的能力。在2019年的繁殖季节，他们在40只雄性茶腹食籽雀和36只雄性伊比利亚食籽雀的领地上安置诱饵雄性。然后，当有雌性在附近时，他们监测“居民们”的反应。

They used four decoys. One had the plumage and song of a male Ibera seedeater. One similarly resembled a male tawny-bellied seedeater. The other two had, in one or other combination, the appearance of one species and the song of the other.

他们用了四种诱饵。一种有着雄性伊比利亚食籽雀的羽毛和鸣啭，一种和雄性茶腹食籽雀相似。另外两种在一种或另一种组合下有着一种物种的外表和另一种物种的鸣啭。

If a resident male viewed a decoy as competition he would act aggressively, by flying to and pecking at it. And males could certainly tell the difference. They were most aggressive towards decoys that resembled their own species, moderately so towards decoys that combined features of both, and least towards those that resembled the other species. Since these were not real birds, it must have been the colouration and the song that were the cues.

如果一只雄性居民把诱饵视为竞争对手，那么他会飞过去啄它，表现得很有攻击性。雄性当然能分辨出区别。它们对与自己种类相似的诱饵最具攻击性，对结合了两者特征的诱饵的攻击性较弱，而对那些与其他种类相似的诱饵的攻击性最低。既然这些不是真正的鸟，那么颜色和鸣啭一定就是线索。

The differences between the species' songs may be cultural, and have come about after the split. But the differences in plumage are clearly genetic. What is more, they are so small that they could have happened on a single occasion as a result of an accidental hybridisation, for similar genetic differences are found in varying combinations throughout southern capuchino seedeaters. Also, what happened once could presumably have happened often. It therefore seems plausible⁶ that Ms Turbeck has uncovered the nub of the mechanism⁷ by which this group has become so diverse. If so, then she has helped write another page in that as-yet-unpublished volume, "The Real Origin of Species".

这两种物种间鸣啭上的差异可能是由文化造成的，而且是在物种分裂之后产生的，但羽毛上的差异显然是遗传的。更重要的是，差异如此之小，所以可能是偶然杂交的结果，因为在南部卡布奇诺食籽雀的不同组合中发现了类似的基因差异。而且，曾经发生过的事情可能会经常发生。因此，图贝克女士揭示了这一群体变得如此多样化的核心机制似乎是合理的。如果是这样的话，那么她又能在尚未出版的《物种的真正起源》一书中再添上一页了。

1 genetic   

adj.遗传的，遗传学的

参考例句：

• It's very difficult to treat genetic diseases.遗传性疾病治疗起来很困难。
• Each daughter cell can receive a full complement of the genetic information.每个子细胞可以收到遗传信息的一个完全补偿物。

2 genes   

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 intriguingly   

参考例句：

• Intriguingly, she gave to the music a developed although oddly malleable personality. 最神奇的是，她的音乐具有成熟却又很奇怪地极富可塑性。 来自互联网
• Intriguingly, the patients brains were riddled with tangles, but not amyloid plaques. 有趣的是，患者的大脑中充满了各缠结，但并没有粉斑。 来自互联网

4 chromosomes   

n.染色体( chromosome的名词复数 )

参考例句：

• Chromosomes also determine the sex of animals. 染色体也决定动物的性别。 来自《简明英汉词典》
• Each of four chromosomes divide longitudinally. 四种染色体的每一种都沿着纵向分裂。 来自《现代汉英综合大词典》

5 syllables   

n.音节( syllable的名词复数 )

参考例句：

• a word with two syllables 双音节单词
• 'No. But I'll swear it was a name of two syllables.' “想不起。不过我可以发誓，它有两个音节。” 来自英汉文学 - 双城记

6 plausible   

adj.似真实的，似乎有理的，似乎可信的

参考例句：

• His story sounded plausible.他说的那番话似乎是真实的。
• Her story sounded perfectly plausible.她的说辞听起来言之有理。

7 mechanism   

n.机械装置；机构，结构

参考例句：

• The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
• The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。