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    本题由lindy提供
2174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 passage suggests that if a grass-dwelling anole lizard species

evolved on one island and then traveled over water to colonize a second island, the grass-dwelling anoles on the two islands would eventually


    A. develop very different DNA sequences 

    B. develop into different species that are more distantly related to each other than to tree- and twig-dwelling anoles on their own islands 

    C. come to differ significantly from one another in habitat use 

    D. develop into different, but closely related, species

    E. evolve significant morphological differences


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答案:
D
suggest推理
文章的主要意思就是一个 这个物种在一个岛上进化了,然后游去了另外一个岛,或者是本来是一个大岛,岛分裂了之后,这个物种的成员被分到了好几个岛上面,那么这种情况的前提都是你只进化了一次,就是在原来那个岛上。这是不同岛 一个物种相似性的解释。 但是这个物种它各自在每个岛也可以自己进行develop,这是同岛,不同物种相似性的解释。 那么看这题,他们在根源上close-related,m但是因为可以在自己岛上发展,会进化的有区别。选D 选项A 本身DNA是不会产生改变的 选项B 错在distantly,应该是closely 选项C habit use 到底是不是有区别,多大区别不知道 选项E 形态特征会不会非常不一样也不清楚

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