A tiny, tree-living thrips is the first species identified that can

Question

A tiny, tree-living thrips is the first species identified that can reproduce both by laying eggs and by bearing live young, although for any one instance of reproduction, a given female will use only one of the two methods. Interestingly, biologists have observed that all of the offspring of this insect that are hatched from eggs are females, and all of the offspring that are live-born are males. It has also been noted that any particular live-born brood will comprise fewer individuals than any particular brood hatched from eggs. However, a much larger proportion of male offspring than of female offspring survives to adulthood, and among thrips reaching adulthood the ratio of males to females is about even.

Which one of the following can be properly inferred about the species of thrips described in the passage?

(A) It is the only species capable of using two different methods of reproduction.

(B) Any female of the species that can reproduce by laying eggs can also reproduce by bearing live young but not necessarily vice versa.

(C) On average, across the species, more of the offspring are born by hatching from eggs than are born live.

(D) For the species as a whole, there are, over time, about as many instances of live-born broods as there are broods hatched from eggs.

(E) There are females that use only one of the two methods of reproduction over the course of their lives.

rajdeep212003 · Answer

I think option C is the best answer here.

The passage says:

• offspring hatched from eggs are all females 
• live-born offspring are all males 
• live-born broods contain fewer individuals than egg broods 
• but more males survive to adulthood, so eventually the adult male:female ratio becomes about equal

From this, we can infer that initially more females must be produced than males.

Why?

Because if the number of females and males produced were already equal at birth, and males survive at a much higher rate, then males would outnumber females in adulthood.

But the passage says the adult ratio becomes approximately even.

So the species must start with more females being produced, and since females come from eggs, it follows that more offspring are produced through eggs than through live birth.

That directly supports option C.

---

Why the other options are weaker:

(A) The passage only says this is the first species identified with both reproductive methods. 
That does NOT mean it is the only species capable of doing so.

(B) The passage never says females that lay eggs can also give live birth. 
It only says a female uses one method for a given reproductive instance.

(D) This talks about the number of broods, not the number of offspring. 
A live-born brood is specifically said to contain fewer individuals, so equal numbers of broods would not help prove anything.

(E) The passage never states that some females use only one method throughout their entire lives. 
It only says that during a particular reproductive instance, a female uses one method.

So C is the only choice that can actually be inferred from the information given in the passage.

— Rajdeep

guddo · Answer

A tiny, tree-living thrips is the first species identified that can reproduce both by laying eggs and by bearing live young, although for any one instance of reproduction, a given female will use only one of the two methods. Interestingly, biologists have observed that all of the offspring of this insect that are hatched from eggs are females, and all of the offspring that are live-born are males. It has also been noted that any particular live-born brood will comprise fewer individuals than any particular brood hatched from eggs. However, a much larger proportion of male offspring than of female offspring survives to adulthood, and among thrips reaching adulthood the ratio of males to females is about even. 
 
Which one of the following can be properly inferred about the species of thrips described in the passage?

The passage says egg-hatched offspring are female, live-born offspring are male, and male offspring survive to adulthood at a much higher rate. Since adult males and females are about equal in number, there must have been  more female offspring initially  to offset their lower survival rate.

(A) It is the only species capable of using two different methods of reproduction.

Wrong. The passage says it is the first species identified with this ability, not the only species with this ability.

(B) Any female of the species that can reproduce by laying eggs can also reproduce by bearing live young but not necessarily vice versa.

Wrong. The passage does not establish this distinction among females.

(C) On average, across the species, more of the offspring are born by hatching from eggs than are born live.

Correct. Egg-hatched offspring are female, and live-born offspring are male. Since males survive at a much higher rate but adults are about evenly split, there must be more female offspring produced at the start. So more offspring are born from eggs than are born live.

(D) For the species as a whole, there are, over time, about as many instances of live-born broods as there are broods hatched from eggs.

Wrong. The passage gives information about offspring numbers and survival rates, not the number of broods of each type.

(E) There are females that use only one of the two methods of reproduction over the course of their lives.

Wrong. The passage says a female uses only one method in any one instance of reproduction, but it does not say some females use only one method for life.

Answer: (C)

yc168 · Answer

OE for reference:

Overview:  
This passage consists of a number of facts about the reproduction of a species of thrips. You are asked to select the answer choice that, given those facts, can be inferred to be true about the reproduction of thrips.

The Correct Answer:

C  The passage says that there are about as many female thrips who reach adulthood as there are male thrips who reach adulthood. It also says that female offspring survive to adulthood at a much lower rate than male offspring do. For females to match males reaching adulthood in overall numbers in spite of the higher rate of deaths for females between birth and early adulthood, there must be more female births overall. Since all females are hatched from eggs and all males are live-born, it follows that, across the species, more of the offspring are born by hatching from eggs than are born live. So if the information presented in the passage is true, (C) must also be true.

The Incorrect Answer Choices

A  The passage does say that the particular species of thrips is the first species to have been identified as being capable of reproducing by the two different methods mentioned. The passage does not claim or imply, however, that no other species uses those two methods. And it says nothing about whether there may be other combinations of two methods of reproduction that some species or other might use. Consequently, (A) cannot be inferred.

B  The passage tells us only that for any one instance of reproduction, a given female will use only one method of reproduction. But this claim is consistent with a wide range of possibilities. For example, it could be that some females reproduce only by laying eggs, some only by bearing live young, and some by different methods on different occasions. Thus (B) cannot be inferred.

D  The passage does not provide enough information to support the claim in (D). For all we are told in the passage, there could be  more  live-born broods over time than broods hatched from eggs. The passage tells us that there are fewer individuals in live-born (i.e., all male) broods than in the (all female) broods hatched from eggs. This is counteracted to some degree by the higher survival rate for males, but we don't know how much. If the higher survival rate for males doesn't fully compensate for the fewer individuals in the live-born broods, then the even ratio of adult males to adult females could only be accounted for if there are more live-born broods over time than broods hatched from eggs.
Furthermore, for all we are told in the passage, there could be  fewer  live-born broods over time than broods hatched from eggs. If the higher survival rate for males overcompensates for the fact that there are fewer individuals in live-born broods, then the even ratio of adult males to adult females could only be accounted for if there are fewer live-born broods over time than broods hatched from eggs.

E  The passage does not provide enough information for (E) to be properly inferred. The passage tells us that "for any one instance of reproduction, a given female will use only one of the two methods," but tells us nothing that suggests that some females use only one method during their lifetimes.

A tiny, tree-living thrips is the first species identified that can

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A tiny, tree-living thrips is the first species identified that can

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