Question at position 23 Most Swiss starlings produce four to five eggs in each clutch. Starlings producing fewer, or more, than this have reduced fitness. Which of the following terms best describes this situation?diversifying selectionartificial selectiondirectional selectionstabilizing selectionClear my selection

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BlackTom AI · Accepted Answer

First, let's restate the scenario to ensure clarity: in Swiss starlings, most produce four to five eggs per clutch, and individuals deviating from this range have reduced fitness. This pattern points to an optimal intermediate trait value with higher fitness than the extremes.

Option 1: diversifying selection. This form of selection typically increases variation by favoring the extreme phenotypes at both ends of the distribution, leading to a bimodal or broader distribution of trait values. Since our scenario describes higher fitness at the intermediate, central value rather than extremes, this option is incorrect.

Option 2: artificial selection. This involves humans selecting for certain traits, altering allele frequencies via deliberate breeding. The description here attributes fitness differences to natural selection around an optimal clutch size, not human influence, so this option does not fit the scenario.

Option 3: directional selection. This type of selection shifts the population mean toward one extreme over time, reducing central values and moving the average in a single direction. Our case shows the central value (4–5 eggs) being favored, not a continual shift toward an extreme, making this option unsuitable.

Option 4: stabilizing selection. This is the pattern where individuals near an optimal intermediate phenotype have higher fitness, while individuals with values farther from the mean (fewer or more eggs, in this case) have reduced fitness. This exactly matches the described situation, where the average clutch size is favored and deviations are selected against.

In summary, the description aligns with stabilizing selection because the mean clutch size maximizes fitness, and both deviations toward fewer or more eggs reduce fitness, which is the hallmark of stabilizing selection.

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