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题库解析   >   主旨题题型   >  
    本题由lindy提供
2037次学习

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.

The primary purpose of the passage is to


    A. describe some unusual features of anole lizard species 

    B. account for a particular type of behavior found among anole lizard species 

    C. contrast two types of evidence that have been used to support a particular hypothesis concerning anole lizard species 

    D. explain how researchers resolved a particular scientific question concerning anole lizard species 

    E. examine different explanations for a particular trait common to certain anole lizard species 


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答案:
D
主旨题 文
主要提出一个现象,存在相似性的问题,对这个相似性进行了2中解释,但是这个相似性是基于只进化了一次的,而实际上不同岛了之后,它们可以自己再develop,就引出了同岛不同物种相似性的问题。整篇文章就是一个问题,对这问题进行解释的结构,选D 选项A describe some unusual features文章未提及、 选项B account for a particular type of behavior解释一个特征行为,与文章内容不符 选项C 对比两种evidence不符 选项E 对于一格particular 特性的不同解释的检测,检测特性与文章内容不符

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