Question

Behavioural ecologists exploring a newly discovered island find 20 new species of terrestrial lizards. Males of these species have a dorsal ridge that varies in size from large in some species to entirely lacking in others. The scientists hypothesise that dorsal ridges in males evolved by runaway sexual selection stemming from sensory bias in females. Which one of the following would provide the necessary evidence to support this hypothesis?

• A. Females of species in which males lack this trait are attracted to males that have a large dorsal ridge artificially attached to them.
• B. Males without a ridge are more likely to attract females of all species than males with a ridge.
• C. Males with a larger dorsal ridge win more fights and get more mates than males with a smaller ridge.
• D. Females of species whose males have a dorsal ridge do not show a preference for this trait.

Hint:

Runaway sexual selection occurs when a trait evolves because of the preference of one sex (usually females) for a particular characteristic in the opposite sex.

Answer 1

The Correct Option is A

The hypothesis proposes that the dorsal ridge evolved due to sensory bias in females, which means females are attracted to males with a certain trait, and over time, this preference leads to the evolution of that trait. To test this hypothesis, we need evidence that females show a preference for males with a large dorsal ridge, even in species where males naturally lack the trait.

Step 1: Analyzing the options.
- (A) This option directly tests the hypothesis. If females are attracted to males with an artificially added large dorsal ridge, this provides evidence that the trait evolved due to sensory bias and sexual selection, rather than natural selection. - (B) This option does not support the hypothesis, as it suggests that males without a ridge attract more females, which contradicts the idea of sexual selection favoring males with the trait. - (C) This option describes a competitive advantage but does not address the preference of females for the trait, which is crucial for the hypothesis. - (D) If females of species whose males have a dorsal ridge do not show a preference, it would contradict the idea of sexual selection driven by female preference for the trait.

Step 2: Conclusion.
The correct answer is (A), as it provides the evidence of female preference for the trait, supporting the hypothesis that the dorsal ridge evolved due to runaway sexual selection driven by sensory bias in females.

Final Answer: (A) Females of species in which males lack this trait are attracted to males that have a large dorsal ridge artificially attached to them.