PrepTest 143, Section 4, Question 1
Among Trinidadian guppies, males with large spots are(47 more words not shown)
The situation described above most(9 more words not shown)
- AA trait that(13 more words not shown)
- BThose organisms that(13 more words not shown)
- CThose organisms that(9 more words not shown)
- DWhether a trait(15 more words not shown)
- EA trait that(11 more words not shown)
Reading the argument
Being attractive won't help much if a predator eats you before you grow up. Large spots give male guppies an advantage with females. At first, that sounds like a straightforward advantage for producing offspring: more mating opportunities. But the same spots make the males easier for predators to notice. Where predators are abundant, the large-spotted males don't survive to maturity.
What we’re looking for
So the spots involve a tradeoff. They help attract a mate but can keep a male from surviving long enough to reproduce. The question asks for a generalization that captures that situation. I'd look for a trait whose apparent benefit can become a disadvantage under different conditions.
Working the answers
- A
We haven't compared the danger to males with the danger to females. All the information about spot size concerns males. A changes the comparison from different spot sizes and environments to different sexes.
- B
Being more attractive doesn't guarantee more offspring. In the predator-filled waters described here, the most attractive males don't even reach maturity. B ignores the obstacle that makes this example interesting.
- C
We aren't told which guppies live longest or how many offspring they ultimately produce. Surviving is relevant to reproduction, but that doesn't establish a rule that the longest-lived organisms have the most offspring. The passage concerns competing effects of a particular trait.
- D
The context matters, but this answer names the wrong part of the context. We know the danger depends on predators in the water. We aren't told how the same trait affects a female guppy, so we can't make the male-versus-female comparison D requires.
- ECorrect
Large spots help with procreation by attracting mates. In an environment full of predators, those same spots hinder procreation by making the males easier to detect and preventing them from reaching maturity. E preserves both sides of the tradeoff instead of assuming an attractive trait must always be helpful.
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