求助TT GWD 11-27 一道阅读题目~

linmeimeiei

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
inmorphology, 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

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

这道题老是想不明白，各位NN们帮忙指点一下啊~~多谢多谢~~~
答案是D，但是我觉得文中明确又说两者并不是closely related，所以我没有选择D。而后我认为文章中并没有讲到说同一个岛上的不同生物的联系可以比不同岛上的由同一生物发展而来的不同生物之间的联系更紧，所以我也没有选B。倒是觉得最后一段里面主要讲了最初一个生物由于去了不同的岛，但是由于independently发展，所以不再closely related， 又根据Species with similar DNA sequences for these genes are generally more closely related to each other than to species with less-similar DNA sequences，觉得应该是具有different DNA sequences...

hz032478

If a grass-dwelling anole lizard species evolved on one island and then traveled over water to colonize a second island, then it is one of the two scenarios which imply that specialization to each niche occurred only once.

If each type of specialist evolved just once, then similar specialists on different islands would be closely related.  

Only Option D says the close relationship.

In Option B, the word "distantly" reverses the intended idea of Option D.

chipmunk

答案在这句话之后，Likewise, the specialists for other habitats are similar across the islands.
    The presence of similar species on different islands could be variously explained.
后面的两段话解释做出了两种解释，1，是anole lizard可能在进化前在同一个岛上，然后或者是游到另外一个岛上，或者是本来的岛分裂了，从而导致anole lizard也分离，在这种情况下，After the islands
separated, the isolated lizard populations would have become distinct species while also retaining their ancestors’ niche adaptations。
紧接着是 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.

也就是说，如果只evolve一次的话，在进化的时候在同一个岛上，但是后来分开的话，虽然他们会成为different species，但是会closely related。
相反，如果他们在一开始就在不同的岛上独立evolve的话，结果就是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.

问题问的是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属于第一种情况，所以答案是D。


简单来说，过程是这样的，有两种情况：
1，在同一个岛上进化，然后分开，这样他们会发展呈different spcies， 但是closely related。
2，在不同的岛上单独分开进化，这样的结果是，在一个岛上的anoles更加closely related to 同一个岛上的其他种类的anoles，而不是不同岛上的相同anoles。