Anole lizard species that occur together (sympatrically) on certain Ca

Question

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.   1 
 D 
1. 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

2 
 B 
2. Which of the following best describes the purpose of the highlighted sentence?

(A) It raises a question about why coexisting anole lizard species occupy the different types of habitats mentioned in the first sentence. 
(B) It introduces a fact about anole lizard species that the passage will go on to explore. 
(C) It identifies a particular aspect of anole lizard behavior that distinguishes anoles from other lizard species. 
(D) It explains why one aspect of anole lizard species' habitat use has been difficult to account for. 
(E) It points out a surprising relationship between morphology and habitat use that is explained in the concluding paragraph.

3 
 A 
3. It can be inferred from 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 from 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.

4 
 D 
4. 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

Source :  SCIENTIFIC AMERICAN 
March 2001
Volume 284, Issue 3

Evolution: A Lizard's Tale 
 On some islands in the Caribbean, evolution seems to have taken the same turn—over and over and over again 
By Jonathan B. Losos
 
 LINK 1  &  LINK 2

JarvisR · Accepted Answer

Hi maggie, My 2 cents on this. Hope this answers ur questions.

BTW wht abt ur timing on this one.Mine was 10 mins and max i cld have squeezed here is to 9 mins.

=========================================== Para-1: Intro abt the Anole lizard and a fact is presented. Para-2: Theory#1 is presented to explain the mentioned fact.And intro abt the theory/explanation#2. Para-3: Discussion is continued from Para2. Para#4: scientists perform some experiment and final conclusion is presented. In nutshell: a unique trait is presented and is then resolved or explained using an experiemnt. ===================================== 1. The primary purpose of the passage is to A. describe some unusual features of anole lizard species -only in starting para. B. account for a particular type of behavior found among anole lizard species - arg is not just abt the description.Its abt identifying the reason behind the mentioned trait. C. contrast two types of evidence that have been used to support a particular hypothesis concerning anole lizard species - No 2 evidences r offered.2 theories r presented and then a conclusion is made. 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- i would prefer D over E. author doesn't check-out/examine the 2 theories. Theories r presented, then an experiment is performed which confirmed one of the theory.

BrightOutlookJenn · Answer

Hi  oasis90

Here are the two sentences we need:

the sentence announcing the main idea:

and the very last sentence, which gives us the resolution to the mystery announced earlier:

When I read the passage and I got to the topic sentence, I said out loud here in my living room, "ooh, how did they get there? hmm!" And then I wondered in my head if Puerto Rico and the neighboring islands were all once connected like a mini-Pangaea or something. OK, I couldn't have said anything out loud in the testing center, but I surely would have said it to myself mentally. Here is the mystery, the drama of our passage.

And then at the end, almost surprisingly,  we actually get an answer  to the question that was posed. That's a little unusual - often GMAT leaves us hanging. But since we get an answer, that's important to note ... just like we should note if the author decides to take a side or declare a winner in an argument where he has spent most of the passage explaining the two sides.

So my summarized main idea is "there was a mystery about how these same types of lizards got distributed so similarly across 4 islands that are, well, islands, there were some theories about how that happened, and at the end some scientists were able to settle on one of the theories."

So, in E, there are two problems. Yes, "trait" is wrong - a trait would be like they all have grey eyes. A trait isn't what we have here at all ... we have a particular pattern of species distribution across islands. But the other problem is that E is neutral and this isn't actually a neutral passage: at the end we actually get told which theory was proven correct. That's crucial information and the main idea answer must reflect that.

Let me know if that clears it up.

megha_2709 · Answer

7 mins ,2 incorrect !!.

Thanks for posting good question. Would further welcome more tips to improve RC

Regards
Megha

RDhin · Answer

Can you please help on the 4th question
I am unable to comprehend it!
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.

How to get that information from the above lines

megha_2709 · Answer

Hi RDhin, Apologies for late response . Below is my explanation for the 4th question. 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 that means closely related species will have similar DNA Sequences for the same genes. They performed an experiment and they found same habitat species on diff island do not have similar DNA sequences which means they are not at all related to each other. for e.g if grass dwellers of 1 island is to be related to grass dweller of another island their DNA sequences should be similar ,but scientist found that DNA sequences for same habitat species on diff island are not similar at all , which led to our conclusion that same habitat species on diff island are not closely related at all and each species evolved independently one each island Now coming to the question: 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 As per the passage if the species evolved only once and travelled to colonize the islands then similar species would have been closely related right ? D States the same that if the above mentioned scenario would have happened then species would be closely related . Hence D is our correct answer. I hope this helps. Please do let me know if you need further help

Regards Megha

abrakadabra21 · Answer

2. Which of the following best describes the purpose of the highlighted sentence? 
A. It raises a question about why coexisting anole lizard species occupy the different types of habitats mentioned in the first sentence.
B. It introduces a fact about anole lizard species that the passage will go on to explore. 
C. It identifies a particular aspect of anole lizard behavior that distinguishes anoles from other lizard species. 
D. It explains why one aspect of anole lizard species' habitat use has been difficult to account for. 
E. It points out a surprising relationship between morphology and habitat use that is explained in the concluding paragraph.

Between B& E, why E is wrong because it explores "surprising relationship between morphology and habitat use"
 
 What is striking _four islands: Puerto Rico, Cuba, Hispaniola, and Jamaica. => same three types of habitat specialists

chetan2u · Answer

Hi,

Refer your PM,
The highlighted portion does tell us that the relationship between morphology and habitat use is not the surprising fact as many other too have the same relationship.
There are changes that occur due to the type of habitat one uses..
It is why same species are found at four different locations.
Now this is a fact and author gives reasoning for it later in the para.
So B shud be correct .

oasis90 · Answer

Hi  jennpt ,

Can you please advise in Q1 why E is wrong? Is it because it says "trait common to certain anole lizard species" when it should be more of a phenomenon (specialist lizards similarities across different islands) then a trait?

1. 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

oasis90 · Answer

Thanks Jenn for your explanation. if I look at the map of the RC as per your layout "there was a mystery about how these same types of lizards got distributed so similarly across 4 islands that are, well, islands, there were some theories about how that happened, and at the end some scientists were able to settle on one of the theories.", I agree 100%. Perhaps the reason I did not choose D was because I felt it focuses too much on the last part  nd at the end some scientists were able to settle on one of the theories  without emphasizing much on the explanations. If Choice D said something like "examine different explanations and explain how researchers resolved a particular scientific question concerning anole lizard species", I would have selected it right away. But I guess this is the closest to it. I do, however, understand that E is neutral and ignores a critical conclusion and element of the passage: the answer to the question the RC is trying to resolve.

Thanks again Jennifer.

Heisenberg12 · Answer

“An ancestral species might have adapted to exploit a particular ecological niche on one island and then traveled over water to colonize other islands.....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.”

The above mentioned lines from the passage provide answer to the 4th question. 
The lines state that in case the anole lizards travelled over water, they would be different species (lines in the passage - “distinct species”) however they would be closely related (lines in the passage - “retaining their niche adaptations”)

Posted from my mobile device

Sarthaktiwari13 · Answer

The thing is that there are no rules regarding the Main Purpose questions. I discarded Option D because how scientists resolved the mystery is only mentioned in PARA 4 and not even once it is mentioned in other paragraphs. Its a common approach in such questions to consider the whole passage hence i didn't chose option D. However , the phenomenon discussed in the passage is not a trait or a behavior and hence B and E should be incorrect.

jainrahul2 · Answer

Can anyone explain the answer for ques 4. I was confused between B and D and eventually marked B

TaN1213 · Answer

The answer lies in the following excerpt from the passage:
"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."

Evolving independently on each island ===> not closely related.
As per Q4, they are travelling to different island ===> So, they will be closely related despite developing into different species due to habitat usage.

dcummins · Answer

Interesting Read.

Passage map:  Anole lizard variations
 P1:  To intro, question and briefly discuss evolutionary phenomenon of Anole lizards and 
 P2:  To explain one potential cause for the phenomenon 
 P3 : To caveat explanation with another reasoning - independent evolution
 P4:  To provide reliable evidence validating one form of reasoning - Independent evolution

Q1 - Main Idea/ Purpose  
A- incorrect. Per map above.
B - Incorrect. Its not behaviour but evolution we are accounting for
C - No two types of evidence are given. Two theories are given.
D - Correct. The question is raised in P1 - "Why are the lizards so similar across different islands?"
E - Incorrect. What trait? We are told of evolutions e.g. stocky + long legs, but no general trait to all lizards.

Q2 - Main Idea/ Purpose  
The highlighted text points out a "striking" point of interest about the lizards - the same 3 types of specialists occur across different geographies. The information about the new geographies is new information.

A - No. The first sentence merely describes the evolutionary traits of the specialists. Sentence 2 doesn't raise a question at all.
B - Correct. This new information is a fact and if you look at the Passage map you will see that the subsequent paragraph attempts to explain this fact, and then finally in P4 conclusive evidence is given to account for this fact.
C - Incorrect - No other lizard species are mentioned.
D - no. What aspect? Habitat use is described in terms of the specialisations, but no specific specialty is pointed out for discussion.
E - No. Look at P4 - it gives DNA as evidence to substantiate for the peculiarity made by the highlighted sentence.

Q3 - Inference  
What's true of TWO OF THE SAME Speciality Lizards? 
Before we go through the answers, here's what we know:
- they aren't related to each other as evidenced by dissimilar DNA
- they're similar habitat use and specialisations are so close that researchers think the species are related.
- they are stocky with long legs (p1)

A - Correct
B - no. They are 'stocky' but have long legs - meaning their torso would be stocky
C - No. we cannot infer this from the information given. We only know that they are similar
D - No. Opposite - they are actually similar.
E - No. As proven by the DNA they are not.

Q4 - Inference  
The question brings to light a forecasted scenario discussed in P2 
A - P4 disproves this theory by the DNA test, so if the theory is true then the DNA would be similar, not dissimilar.
B - No. The specialist lizards share commonalities with other specialists
C - False. We know the whole reason for this article is to account for the similarities. Same logic applies to E
D - Yes. P2 states "the isolated lizard populations would have become distinct species while also retaining their ancestors' niche adaptations" if current day lizards shared the same DNA (i.e. were descendants)
E - No- habitat use and morphology would be very similar if not the same

kirudang · Answer

Anyone could help me with Q3:
This is inference question.
 Paragraph 3:  
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 .
 Paragraph 4:  DNA indicating that specialists  evolved independently  on each island.

Question asks us to compare same specialist in 2 islands.
From 3 and 4, we can induce that they are different, since they are already evolved independently -> D makes sense?

If A is true, could you quote it?

siddhantvarma · Answer

Answer to 3rd question lies in the first para:
 
Tree dwellers are stocky and have long legs that's exactly what (A) says. " (A) They share a morphology characterized by stocky bodies and long legs."

Anole lizard species that occur together (sympatrically) on certain Ca

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Anole lizard species that occur together (sympatrically) on certain Ca

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