Anole lizard species that occur together (sympatrically) on certain

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. 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. 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. 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. 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

Show Spoiler

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

Attachment:

scientificamerican0301-64.pdf [1.22 MiB]
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Show Answer Question #1

Official Answer

D

Show Answer Question #2

Official Answer

B

Show Answer Question #3

Official Answer

A

Show Answer Question #4

Official Answer

D

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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.

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

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

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."

kartickdey · Answer

GMATNinja   KarishmaB  I have the following query regarding Q1:
As it is stated in the passage that the anole lizards have developed independently, what is the cause of the similarities among each of the anole specialist on the four islands have not been discussed in the passage; then how option D can be right?

guddo · Answer

1. The primary purpose of the passage is to

The passage presents a puzzle (similar habitat specialists on four islands), lays out possible explanations, explains what each explanation would predict about evolutionary relatedness, and then says DNA evidence resolved the issue by showing specialists evolved independently on each island.

(A) describe some unusual features of anole lizard species

The passage starts with unusual features, but it does not stop there; it uses them to set up and answer a specific question.

(B) account for a particular type of behavior found among anole lizard species

Behavior is mentioned only as part of “similarity,” not as the central focus.

(C) contrast two types of evidence used to support a hypothesis

The passage does not mainly contrast two evidence types; it explains predictions and then reports DNA evidence.

(D) explain how researchers resolved a particular scientific question concerning anole lizard species

Yes. It walks through the question, competing scenarios, the test (relatedness predictions), and the DNA based conclusion.  This is the main purpose.

(E) examine different explanations for a particular trait common to certain anole lizard species

It does examine explanations, but it also goes further and shows how the question was resolved. So (D) is more complete.

Answer: (D)

guddo · Answer

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

The highlighted sentence says what is “striking”: not that sympatric species differ, but that the same three habitat specialist types occur on each of four islands. That sets up the main puzzle the rest of the passage investigates and resolves.

(A) It raises a question about why coexisting anole lizard species occupy the different types of habitats mentioned in the first sentence.

No. It explicitly says those differences are common and not the striking part.

(B) It introduces a fact about anole lizard species that the passage will go on to explore.

Yes. It introduces the key surprising fact (parallel sets of specialists across islands), which the passage then explains with alternative scenarios and DNA evidence.  This is exactly its role.

(C) It identifies a particular aspect of anole lizard behavior that distinguishes anoles from other lizard species.

It is about distribution of habitat specialists across islands, not a unique behavior.

(D) It explains why one aspect of habitat use has been difficult to account for.

It does not say it has been difficult; it says it is striking.

(E) It points out a surprising relationship between morphology and habitat use that is explained in the concluding paragraph.

The concluding paragraph is about DNA relatedness, not explaining a morphology habitat relationship.

Answer: (B)

guddo · Answer

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?

The passage says that on each island the same three habitat specialists occur, and that specialists for the same habitat are similar across islands. It also gives the morphology for tree dwellers: stocky with long legs. Finally, it says DNA evidence shows same-habitat specialists on different islands are not closely related.

(A) They share a morphology characterized by stocky bodies and long legs.

Yes. Tree dwellers are described as stocky with long legs, and the passage says the specialists for other habitats are similar across islands.  So Cuban and Jamaican tree dwellers share that morphology.

(B) They have bodies that are relatively slender compared to their stubby legs.

That describes twig dwellers, not tree dwellers.

(C) They differ significantly from one another in size.

Size is never discussed.

(D) They differ significantly from one another in behavior and habitat use.

The passage suggests the opposite: same habitat specialists are similar in habitat use (and at least the twig case mentions behavior similarity too).

(E) They are genetically closely related to one another.

The DNA evidence says the opposite: similar specialists on different islands are not closely related.

Answer: (A)

guddo · Answer

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

In that scenario, one grass specialist spreads to another island, and then the two populations become isolated. The passage says isolation would lead them to become distinct species while still keeping the same niche adaptations, and they would remain closely related because specialization happened only once.

(A) develop very different DNA sequences

Not supported. They may diverge, but the passage’s point is about relative relatedness, not that their DNA must become “very different.”

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

This contradicts the passage: if specialization happened once, the two grass species on different islands would be closer to each other than to other habitat types.

(C) come to differ significantly from one another in habitat use

Not supported. They would both remain grass specialists, since they retain their ancestors’ niche adaptations.

(D) develop into different, but closely related, species

This matches exactly: after isolation they become different species, but because they share a single origin as grass specialists, they remain  closely related .

(E) evolve significant morphological differences

Not suggested. They are expected to retain the grass-specialist morphology rather than diverge dramatically.

Answer: (D)

Anole lizard species that occur together (sympatrically) on certain

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Anole lizard species that occur together (sympatrically) on certain

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