Understanding Sexual Selection Models

Sexual selection is a type of natural selection where individuals compete for access to mates, and this competition can lead to the evolution of exaggerated traits, particularly in males. The question asks us to match two specific models of sexual selection, Runaway Selection and Chase-away selection, with their descriptions.

Runaway Selection Explained

Runaway Selection, also known as Fisherian runaway, is a model proposed by R.A. Fisher. It suggests that a female preference for a particular male trait and the male trait itself can become genetically associated. Once this association exists, a positive feedback loop can begin. Females who prefer the trait will mate with males who have the trait. Their offspring will inherit both the preference (from the mother) and the trait (from the father). This leads to an increase in the frequency of both the preference and the trait in the population, potentially leading to exaggerated male traits.

Looking at the descriptions in Column Q:

• (i) Males exploit a pre-existing sensory bias in females. Females choosing such males have higher quality offspring. (This doesn't describe a positive feedback loop driving exaggeration based on preference.)
• (ii) Female choice for male trait occurs due to perceptual errors leading to poor quality offspring. Thus, females will evolve to run away from males with such traits. (This describes negative consequences and avoidance, not runaway escalation.)
• (iii) Female choice for male trait results in a positive feedback loop favouring both, males with such trait and females that prefer them. (This perfectly matches the description of Runaway Selection.)
• (iv) Males exploit pre-existing sensory bias in females. Females do not benefit by choosing such males, driving the evolution of females that discriminate against such males. (This describes exploitation and resistance, not runaway.)

Therefore, Runaway Selection (A) is best described by (iii).

Chase-away Selection Explained

Chase-away selection is another model explaining the evolution of male traits and female preferences. It often starts with males evolving traits that exploit a pre-existing sensory bias in females. Initially, this exploitation might not provide any benefit to the female, or it might even be costly (e.g., leading to poor offspring). Because the male trait exploits a female's bias without providing benefits, there is selection on females to evolve resistance or to become less responsive to the male trait. This leads to an evolutionary arms race: males evolve more exaggerated traits to overcome female resistance, and females evolve stronger resistance or discrimination.

Looking at the descriptions in Column Q again:

• (i) Males exploit a pre-existing sensory bias in females. Females choosing such males have higher quality offspring. (Females benefiting contradicts the chase-away concept where females often do not benefit or are harmed.)
• (ii) Female choice for male trait occurs due to perceptual errors leading to poor quality offspring. Thus, females will evolve to run away from males with such traits. (This describes poor outcomes and female avoidance, which is a component of the female evolving resistance phase.)
• (iii) Female choice for male trait results in a positive feedback loop favouring both, males with such trait and females that prefer them. (This is Runaway Selection, not Chase-away.)
• (iv) Males exploit pre-existing sensory bias in females. Females do not benefit by choosing such males, driving the evolution of females that discriminate against such males. (This describes the key components of chase-away: male exploitation of sensory bias, lack of female benefit, and subsequent female evolution of discrimination/resistance.)

While (ii) describes a potential negative outcome and female response, (iv) more broadly and accurately describes the underlying dynamic of exploitation of bias and the subsequent evolution of female resistance/discrimination, which is central to the "chase-away" arms race. Therefore, Chase-away selection (B) is best described by (iv).

Matching the Models

Based on the analysis:

• A. Runaway Selection corresponds to description (iii).
• B. Chase-away selection corresponds to description (iv).

The correct match is A-iii and B- iv.