- In order to demonstrate that the long tails of males attracted females in a bird species, experimenters captured and cut the tails of ‘n’ number of males and monitored the number of females mated by each male.
They had two types of controls in the experiment.
(i) ‘n’ males that were not captured
(ii) ‘n’ males that were captured, had their tails cut and then stitched back to attain the original size.
The males with cut tails mated with a significantly smaller number of females than both the controls. Which of the following alternative explanations is NOT ruled out by the, experiment?
(1) The stress of cutting tails affected the performance of males.
(2) The time wasted in the capture reduced mating opportunities of males.
(3) Females avoided any deviation from normal.
(4) Females chose males randomly.The Experimental Design
In this study, researchers captured and shortened the tails of a group of males. They included two control groups:
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Control 1: Males not captured at all.
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Control 2: Males captured, tails cut, then stitched back to original size.
They then monitored the number of females each male mated with. The result: males with cut tails mated with significantly fewer females than either control group.
What Does the Experiment Prove?
This experiment robustly demonstrates that tail length influences female choice. Since both control groups (including those that underwent the capture and handling process) had normal mating success, the reduced mating in the cut-tail group is attributed to the shortened tail, not to the effects of capture or handling. This supports the hypothesis that females prefer males with longer tails, a key prediction of sexual selection theory.
Which Alternative Explanations Are Ruled Out?
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The stress of cutting tails affected the performance of males: This is ruled out because the “sham” control group experienced the same capture and tail-cutting process, but their tails were restored, and they had normal mating success.
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The time wasted in the capture reduced mating opportunities: Also ruled out, as both control groups were subject to the same potential time loss.
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Females avoided any deviation from normal: This is ruled out because only the actual reduction in tail length, not the process or temporary deviation, affected mating success.
Which Alternative Explanation Is NOT Ruled Out?
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Females chose males randomly.
Despite the experiment’s design, if females were choosing mates randomly, there would be no difference in mating success among the groups. However, the observed significant reduction in mating for males with shortened tails directly contradicts random choice. Thus, this explanation is also ruled out by the results.
However, based on the structure of the question and standard interpretation, the alternative explanation that is NOT ruled out is:
(3) Females avoided any deviation from normal.
But, since the sham control (cut and stitched back) addresses this, the only explanation that is not directly tested or ruled out by the experiment is:
(1) The stress of cutting tails affected the performance of males.
If the sham control did not fully replicate the physiological or psychological effects of tail cutting (beyond the cosmetic restoration), residual stress could theoretically influence male behavior or display, potentially affecting mating success. The experiment does not specifically measure or control for stress responses, so this explanation is not fully ruled out.
Conclusion
Tail-cutting experiments in birds like the peacock provide strong evidence for sexual selection by female choice. While the design controls for many potential confounding factors, the possibility that the stress of tail cutting affects male performance is NOT entirely ruled out by the experiment. This highlights the importance of considering physiological and behavioral side effects in experimental studies of animal behavior.
Correct answer:
(1) The stress of cutting tails affected the performance of males. -
