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 320 kilometres away. At higher elevations, and only on Sao Tomé, is found the very closely-related Drosophila santomea. The two species can hybridise, 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 description states that D. santomea is found only at higher elevations on Sao Tomé, while D. yakuba inhabits the island's lowlands and can also be found on the African mainland. This suggests that the two species may have diverged due to habitat differentiation, with D. santomea evolving to occupy a different ecological niche at higher elevations. Neither allopolyploidy nor autopolyploidy are suggested in the paragraph, and there is no mention of sexual selection as a factor in the divergence of these two fruit fly species.

On the Volcanic, Equatorial West African Island of Sao Tomé