Biologist Elena Moretti and her team studied two populations of tree frogs. One population lives in a noisy urban environment, while the other lives in a quiet rural forest. The researchers found that urban male frogs produce a mating call with a significantly higher pitch than rural males. The researchers hypothesize that females prefer the pitch that is most audible in their specific environment, and that this preference is driving the two populations to genetically diverge.
Which finding, if true, would most directly bolster the researchers' hypothesis?
Urban frogs have developed larger vocal sacs than rural frogs to increase the volume of their calls.
Over several generations, the pitch of urban male calls has consistently risen, while rural calls remain deep, mirroring the specific auditory preferences of females in each zone.
Tree frogs are capable of altering their call pitch temporarily when moved from one environment to another.
The mating frequency of urban and rural frogs has remained consistent despite the environmental differences.
Correct Answer: B
Choice B is the best answer. The hypothesis is that female preference for audible pitch is driving "genetic divergence." If the calls of urban males are consistently rising over generations while rural calls stay deep (mirroring female preference), this indicates an evolutionary divergence based on those preferences.
Choice A discusses a physical adaptation (vocal sacs) for volume, not the pitch change driving speciation. Choice C suggests the change is temporary/plastic (behavioral), not genetic/evolutionary, which would weaken the hypothesis of speciation. Choice D suggests no change in reproductive behavior, which contradicts the idea of divergence.