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.
It can be inferred form the passage that which of the following is true of the Cuban tree-dwelling anole lizard and the Jamaican tree-dwelling anole lizard?
A.They share a morphology characterized by stocky bodies and long legs.
B.They have bodies that are relatively slender compared to their stubby legs.
C.They differ significantly form one another in size.
D.They differ significantly from one another in behavior and habitat use.
E.They are genetically closely related to one another.
答案是A A 是对的，但是为什么E 错呢？我问了好几个人也没给我一个清楚的解释。。就说A更清楚。。
求NN！！！作者: sunzehua700 时间: 2012-4-26 06:29
我觉得RC就是CR的低级版本，这类RC题类似于CR中的must be true题。
先看A选项，从文中的tree dwellers are stocky with long legs以及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. 我们可以得出A是对的.
嗯我懂为什么错了~E选项我是通过第二段判断出来的，但是Biologists can infer how species are related evolutionarily by comparing DNA sequences for the same genes in different species，是用same genes，观察DNA sequences 相似程度来判断，E应该是Their DNA sequences are similar to one another 就对了吧。
不过这道题正确答案很明显，应该定位在第一段的。作者: taotao35 时间: 2012-4-27 06:45
最后一句话：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. 充分说明不同岛上的基因不同。作者: avenue5th 时间: 2012-4-28 20:37
