A population of beach mice varies in fur color from light to dark.

Dark-colored mice have low relative fitness because hawks are better able to see them against the light-colored sand.

Light-colored mice also have low relative fitness because they are at a higher risk of developing skin cancer. Their light fur offers less protection against UV damage from the intense sun.

Based on this information, what statement best describes the pattern of selection in this population of mice?

Question

A population of beach mice varies in fur color from light to dark.

Dark-colored mice have low relative fitness because hawks are better able to see them against the light-colored sand.

Light-colored mice also have low relative fitness because they are at a higher risk of developing skin cancer. Their light fur offers less protection against UV damage from the intense sun.

Based on this information, what statement best describes the pattern of selection in this population of mice?

BlackTom AI · Accepted Answer

The question presents a scenario where both very dark and very light fur colors have reduced fitness, while intermediate fur colors have higher fitness due to predation and UV-related cancer risks. This setup points to stabilization, where extreme phenotypes are selected against and the average phenotype is favored.

Option 1: 'The mice are experiencing directional selection and darker-colored mice will decrease in frequency.' Directional selection would imply a consistent shift toward one extreme (e.g., darker or lighter). Here, both extremes have low fitness, so there isn’t a unidirectional shift toward darker individuals. This makes this option incorrect.

Option 2: 'The mice are experiencing stabilizing selection and intermediate colored mice will increase in frequency.' This matches the described pattern: both ends (dark and light) are at a disadvantage, while intermediates have higher fitness due to a balance between predation visibility and UV protection. This is the correct interpretation of stabilizing selection in this context.

Option 3: 'The mice are not experiencing natural selection.' Given the differential fitness described (dark and light colors have lower fitness than intermediates), natural selection is clearly acting on the population. Therefore this statement is false.

Option 4: 'The mice are experiencing diversifying selection and both darker-colored and light-colored mice will increase in frequency.' Diversifying (disruptive) selection would increase the frequencies of both extremes, while reducing intermediates. The description provides the opposite: intermediates fare better. Hence this option is inaccurate.

Option 5: 'The mice are experiencing directional selection and light-colored mice will decrease in frequency.' This would imply a shift toward darker coloration, but the data show that dark coloration also yields low fitness. Therefore this directional pattern does not fit the scenario.

In summary, the only option that coherently aligns with the described fitness pattern—extremes being less fit and intermediates more fit—is Option 2, describing stabilizing selection with an increase in intermediate-colored mice.

BIOL 1001 (001-013) Exam 2: Unit 2

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