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On the Bahamian island of Andros, mosquitofish populations live in various, now-isolated freshwater ponds that were once united. Currently, some predator-rich ponds have mosquitofish that can swim in short, fast bursts; other predator-poor ponds have mosquitofish that can swim continuously for a long time. When placed together in the same body of water, the two kinds of female mosquitofish exhibit exclusive breeding preferences.
Which two of the following have operated to increase divergence between mosquitofish populations on Andros?
1) improved gene flow
2) bottleneck effect
3) sexual selection
4) founder effect
5) natural selection
A) 1 and 3
B) 2 and 3
C) 2 and 4
D) 3 and 5

Question

Quizplus · Accepted Answer

The presence of predators in some ponds and their absence in others has created distinct selective pressures for the mosquitofish populations. Mosquitofish in predator-rich ponds have evolved the ability to swim in short, fast bursts to avoid predation, while those in predator-poor ponds have evolved the ability to swim continuously for a long time. This represents natural selection operating to increase divergence between the two populations. The fact that the two populations exhibit exclusive breeding preferences when placed together suggests that sexual selection is also playing a role. Improved gene flow would work against the formation of distinct populations, so it is not operating to increase divergence. The bottleneck effect and founder effect both involve the loss of genetic diversity, which could lead to genetic differentiation between populations, but there is no evidence to suggest they are operating in this case.

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