[Campbell Biology P.549] In the context of frequency-dependent selection, how does the frequ... | Practice Question

In the context of frequency-dependent selection, how does the frequency of left- and right-mouthed scale-eating fish change over time?

  • A: Selection favors the less common mouth phenotype, causing the frequencies to oscillate around 50%.
  • B: Selection consistently favors the more common mouth phenotype, leading to its increase.
  • C: One mouth phenotype is eventually eliminated from the population.
  • D: Environmental factors dictate a fixed 75% left-mouthed and 25% right-mouthed ratio.

Explanation

The text states: 'Prey species guard against attack from whatever phenotype of scale-eating fish is most common. Thus, from year to year, selection favors whichever mouth phenotype is least common. As a result, the frequency of left- and right-mouthed fish oscillates over time, and this balancing selection keeps the frequency of each phenotype close to 50%.'