非洲现存两个品种的大象
文章来源:未知 文章作者:meng 发布时间:2010-12-22 03:15 字体: [ ]  进入论坛
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Contrary to the belief of many scientists (as well as many members of the public), new research confirms that Africa has two—not one—species of elephant. Scientists from Harvard Medical School, the University of Illinois, and the University of York in the United Kingdom used genetic1 analysis to prove that the African savanna2(热带草原) elephant and the smaller African forest elephant have been largely separated for several million years. The researchers, whose findings appear online in PLoS Biology, compared the DNA3 of modern elephants from Africa and Asia to DNA that they extracted from two extinct species: the woolly mammoth4(猛犸象,长毛象) and the mastodon(乳齿象) . Not only is this the first time that anyone has generated sequences for the mastodon nuclear genome, but it is also the first time that the Asian elephant, African forest elephant, African savanna elephant, the extinct woolly mammoth, and the extinct American mastodon have been looked at together.

"Experimentally, we had a major challenge to extract DNA sequences from two fossils—mammoths and mastodons—and line them up with DNA from modern elephants over hundreds of sections of the genome," says research scientist Nadin Rohland of the Department of Genetics at Harvard Medical School.

According to David Reich, associate professor in the same department, "The surprising finding is that forest and savanna elephants from Africa—which some have argued are the same species—are as distinct from each other as Asian elephants and mammoths."

Researchers only had DNA from a single elephant in each species, but had collected enough data from each genome to traverse(穿过,横越) millions of years of evolution to the time when elephants first diverged5 from each other.

"The divergence6 of the two species took place around the time of the divergence(分歧) of the Asian elephant and woolly mammoths," says Professor Michi Hofreiter, who specializes in the study of ancient DNA in the Department of Biology at York. "The split between African savanna and forest elephants is almost as old as the split between humans and chimpanzees. This result amazed us all."

The possibility that the two might be separate species was first raised in 2001, but this is the most compelling(引人注目的,强制的) scientific evidence so far that they are indeed distinct.

Previously7, many naturalists8 believed that African savanna elephants and African forest elephants were two populations of the same species, despite the significant size differences. The savanna elephant has an average shoulder height of 3.5 meters whereas the forest elephant has an average shoulder height of 2.5 meters. The savanna elephant weighs between six and seven tons, roughly double the weight of the forest elephant.

DNA analysis revealed a wide range of genetic diversity within each species. The savanna elephant and woolly mammoth have very low genetic diversity, Asian elephants have medium diversity, and forest elephants have very high diversity. Researchers believe that this is due to varying levels of reproductive competition among males.

"We now have to treat the forest and savanna elephants as two different units for conservation purposes," says Alfred Roca, assistant professor in the Department of Animal Sciences at the University of Illinois. "Since 1950, all African elephants have been conserved9 as one species. Now that we know the forest and savanna elephants are two very distinctive10 animals, the forest elephant should become a bigger priority for conservation purposes."



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1 genetic PgIxp     
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 savanna bYbxZ     
n.大草原
参考例句:
  • The savanna is also the home of meat-eaters--the lion,leopard,and hyena who feed on the grasseaters.大草原也是食肉动物的家乡--狮子、豹、鬣狗--它们都是以草食动物维持生命的。
  • They sped upon velvet wheels across an exhilarant savanna.他们的马车轻捷地穿过一片令人赏心悦目的大草原。
3 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。
4 mammoth u2wy8     
n.长毛象;adj.长毛象似的,巨大的
参考例句:
  • You can only undertake mammoth changes if the finances are there.资金到位的情况下方可进行重大变革。
  • Building the new railroad will be a mammoth job.修建那条新铁路将是一项巨大工程。
5 diverged db5a93fff259ad3ff2017a64912fa156     
分开( diverge的过去式和过去分词 ); 偏离; 分歧; 分道扬镳
参考例句:
  • Who knows when we'll meet again? 不知几时咱们能再见面!
  • At what time do you get up? 你几时起床?
6 divergence kkazz     
n.分歧,岔开
参考例句:
  • There is no sure cure for this transatlantic divergence.没有什么灵丹妙药可以消除大西洋两岸的分歧。
  • In short,it was an age full of conflicts and divergence of values.总之,这一时期是矛盾与价值观分歧的时期。
7 previously bkzzzC     
adv.以前,先前(地)
参考例句:
  • The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
  • Let me digress for a moment and explain what had happened previously.让我岔开一会儿,解释原先发生了什么。
8 naturalists 3ab2a0887de0af0a40c2f2959e36fa2f     
n.博物学家( naturalist的名词复数 );(文学艺术的)自然主义者
参考例句:
  • Naturalists differ much in determining what characters are of generic value. 自然学者对于不同性状决定生物的属的含义上,各有各的见解。 来自辞典例句
  • This fact has led naturalists to believe that the Isthmus was formerly open. 使许多自然学者相信这个地蛱在以前原是开通的。 来自辞典例句
9 conserved d1dc02a3bfada72e10ece79fe3aa19af     
v.保护,保藏,保存( conserve的过去式和过去分词 )
参考例句:
  • He conserved his energy for the game. 他为比赛而养精蓄锐。 来自《简明英汉词典》
  • Under these conditions, the total mechanical energy remains constant, or is conserved. 在这种条件下,总机械能保持不变或机械能保存。 来自辞典例句
10 distinctive Es5xr     
adj.特别的,有特色的,与众不同的
参考例句:
  • She has a very distinctive way of walking.她走路的样子与别人很不相同。
  • This bird has several distinctive features.这个鸟具有几种突出的特征。
TAG标签: species elephant DNA Africa
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