TT GWD 11-27

sunqimin

Q24 to Q27:

      Anole lizard species that

       occur together (sympatrically)

       on certain Caribbean islands

Line       occupy different habitats:

  (5)      some live only in the grass,

some only on tree trunks, and

some only on twigs.  These

species also differ morpho-

logically:  grass dwellers are

 (10)      slender with long tails, tree

dwellers are stocky with long

legs, twig dwellers are slender

but stubby-legged.  What is

striking about these lizards

 (15)      is not that coexisting species

differ in morphology and habi-

tat use (such differences are

common among closely related

sympatric species), but that

 (20)      the same three types of habi-

       tat specialists occur on each

       of four islands:  Puerto Rico,

Cuba, Hispaniola, and Jamaica.

Moreover, the Puerto Rican

 (25)      twig species closely resembles

the twig species of Cuba,

Hispaniola, and Jamaica in

morphology, habitat use, and

behavior.  Likewise, the spe-

 (30)      cialists for other habitats are

similar across the islands.

      The presence of similar

       species on different islands

could be variously explained.

 (35)
                       An ancestral species might

have adapted to exploit a

particular ecological niche on

one island and then traveled

      over water to colonize other

 (40)     islands.  Or this ancestral

species might have evolved

at a time when the islands

were connected, which some

of these islands may once

 (45)      have been.  After the islands

separated, the isolated lizard

populations would have become

distinct species while also

retaining their ancestors’ niche

 (50)      adaptations.  Both of these

scenarios imply that speciali-

zation to each niche occurred

only once.  Alternatively, each

specialist could have arisen

 (55)      independently on each of the

islands.

      If each type of specialist

evolved just once, then similar

specialists on different islands

 (60)      would be closely related.

Conversely, if the specialists

evolved independently on each

island, then a specialist on one

island would be more closely

 (65)      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.

 (70)            Biologists can infer how

species are related evolu-

tionarily by comparing DNA

sequences for the same genes

in different species.  Species

 (75)      with similar DNA sequences

for these genes are generally

more closely related to each

other than to species with less-

similar DNA sequences.  DNA

(80)         evidence concerning the anoles

led researchers to conclude

that habitat specialists on one

island are not closely related

to the same habitat specialists

(85)         elsewhere, indicating that spe-

cialists evolved independently

on each island.

 

Q27:

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

 

1. develop very different DNA sequences
2. develop into different species that are more distantly related to each other than to tree- and twig-dwelling anoles on their own islands
3. come to differ significantly from one another in habitat use
4. develop into different, but closely related, species
5. evolve significant morphological differences

答案是D，D对，但是为什么B不对呀，请各位NN指点一下！！！

还有不好意思问一下，TT GWD31套和GWD的对应关系，我TT GWD每题都搜索的，好多搜不到，有没有什么好的对应方法~~~，谢谢

sunqimin

再看了一变题目，有点懂了，题目的意思是"on one land theory"和“travel theory"结合，也就是第2段第3段结合~~，所以选B。D说的意思只有第3段意思。