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题库解析   >   现象解释型题型   >   RC25-28篇
    本题由lindy提供
1895次学习
RC25-28篇

Anole lizard species that occur together (sympatrically) on certain Caribbean islands occupy different habitats: some live only in the grass,

some only on tree trunks, and some only on twigs. These species also differ morphologically: grass dwellers are slender with long tails, tree dwellers are stocky with long legs, twig dwellers are slender but stubby-legged. What is striking about these lizards is not that coexisting species differ in morphology and habitat use (such differences are common among closely related sympatric species), but that the same three types of habitat specialists occur on each of four islands: Puerto Rico, Cuba, Hispaniola, and Jamaica. Moreover, the Puerto Rican twig species closely resembles the twig species of Cuba, Hispaniola, and Jamaica in morphology, habitat use, and behavior. Likewise, the specialists for other habitats are similar across the islands. The presence of similar species on different islands could be variously explained. An ancestral species might have adapted to exploit a particular ecological niche on one island and then traveled over water to colonize other islands. Or this ancestral species might have evolved at a time when the islands were connected, which some of these islands may once have been. After the islands separated, the isolated lizard populations would have become distinct species while also retaining their ancestors’ niche adaptations. Both of these scenarios imply that specialization to each niche occurred only once. Alternatively, each specialist could have arisen independently on each of the islands.

If each type of specialist evolved just once, then similar specialists on different islands would be closely related. Conversely, if the specialists evolved independently on each island, then a specialist on one island would be more closely related to other types of anoles on the same island—regardless of their ecological niches— than it would be to a similar specialist on a different island. Biologists can infer how species are related evolutionarily by comparing DNA sequences for the same genes in different species. Species with similar DNA sequences for these genes are generally more closely related to each other than to species with less-similar DNA sequences. DNA evidence concerning the anoles led researchers to conclude that habitat specialists on one island are not closely related to the same habitat specialists elsewhere, indicating that specialists evolved independently on each island.

Which of the following best describes the purpose of

the sentence in highlight (“What is … Jamaica”)?


    A. It raises a question about why coexisting anole lizard species occupy the different types of habitats mentioned in the first sentence. 

    B. It introduces a fact about anole lizard species that the passage will go on to explore. 

    C. It identifies a particular aspect of anole lizard behavior that distinguishes anoles from other lizard species. 

    D. It explains why one aspect of anole lizard species’ habitat use has been difficult to account for. 

    E. It points out a surprising relationship between morphology and habitat use that is explained in the concluding paragraph. 


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答案:
B
高亮部分是
说真正striking的不是什么,而是什么这样一个事实, 真正stricking的是不同岛的同物种很相似。而且后面对这一事实进行了2种解释,为什么会相似。选B 选项A raise a question不符 选项C other lizard apecies未提及 选项D 并不是在解释问题,而是只是在陈述一个事实 选项E a surprising relationship between morphology and habitat use that is explained in the concluding paragraph.与文章内容不符

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