The following questions refer to the description below.
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 200 miles away. At higher elevations, and found 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.
-If the low number of hybrid flies in the hybrid zone, relative to the number of D. santomea flies there, is due to the fact that hybrids are poorly adapted to conditions in the hybrid zone, and if fewer hybrid flies are produced with the passage of time, this is most likely to lead to
A)fusion.
B)reinforcement.
C)stability.
D)further speciation events.

Question

Quizplus · Accepted Answer

Reinforcement is the process by which natural selection favors the evolution of prezygotic isolating mechanisms that prevent the formation of unfit hybrids. In this case, if hybrids are poorly adapted to conditions in the hybrid zone and fewer hybrid flies are produced over time, natural selection would favor the evolution of stronger reproductive barriers between the two species. This would result in reinforcement of the species boundary and a decrease in hybridization, ultimately leading to greater species divergence.

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