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On the volcanic, equatorial West African island of Sao Tomé, two species of fruit fly exist. Drosophila yakuba inhabits the island's lowlands and is also found on the African mainland, located about two hundred miles away. At higher elevations, and only on Sao Tomé, is found the very closely related Drosophila santomea. The two species can hybridize, though male hybrids are sterile. A hybrid zone exists at middle elevations, though hybrids there are greatly outnumbered by D. santomea. Studies of the two species' nuclear genomes reveal that D. yakuba on the island is more closely related to mainland D. yakuba than to D. santomea (2n = 4 in both species). Sao Tomé rose from the Atlantic Ocean about 14 million years ago.
Using only the information provided in the paragraph, which of the following is the best initial hypothesis for how D. santomea descended from D. yakuba?
A) allopolyploidy
B) autopolyploidy
C) habitat differentiation
D) sexual selection

Question

Quizplus · Accepted Answer

The most likely explanation given the information provided is habitat differentiation, as D. santomea is only found at higher elevations on Sao Tomé and is closely related to D. yakuba. This suggests that some populations of D. yakuba on the island may have adapted to the new environmental conditions over time, leading to the evolution of D. santomea. There is no evidence in the paragraph to suggest polyploidy or sexual selection as the cause of speciation in this case.

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