Question

Males of the swordtail fish \textit{Xiphophorus helleri possess long tails, while those of \textit{X. maculatus} do not. Females of \textit{X. helleri} prefer males with longer tails. Interestingly, experimental studies show that females of \textit{X. maculatus} prefer \textit{X. maculatus} males with attached artificial long tails over those without.} If the long-tailed \textit{Xiphophorus species evolved from ancestors that lacked a long tail, which one of the following processes best explains the evolution of the observed preference among \textit{X. maculatus} females?}

• A. Kin selection
• B. Sensory bias
• C. Group selection
• D. Runaway selection

Hint:

To analyze mate preferences: 1. Sensory bias occurs when preferences evolve before the corresponding trait appears.
2. Runaway selection involves a feedback loop between traits and preferences within a population.
3. Consider whether the trait is present or absent in the population to differentiate between these processes.

Answer 1

The Correct Option is B

Step 1: Understand the concept of sensory bias. Sensory bias refers to the preference for a particular trait in one sex, arising due to pre-existing sensory or neurological mechanisms. This bias evolves before the trait itself and can influence mate choice when the trait becomes present in the population. Step 2: Evaluate the given scenario.
In this case, females of \textit{X. maculatus}, which do not have long-tailed males in their species, still show a preference for males with artificially attached long tails.
This suggests that the preference for long tails existed prior to the evolution of the trait, making sensory bias the most plausible explanation.
Step 3: Analyze the other options. Option (A) Kin selection: Incorrect. Kin selection involves increasing the reproductive success of relatives, which is unrelated to this observed mating preference. Option (B) Sensory bias: Correct. The pre-existing preference in \textit{X. maculatus} females for long tails, despite the absence of the trait in their species, aligns with sensory bias. Option (C) Group selection: Incorrect. Group selection focuses on the survival and reproductive success of groups, not individual mating preferences. Option (D) Runaway selection: Incorrect. Runaway selection involves a positive feedback loop between trait exaggeration and preference within a population where the trait is already present. Here, the trait (long tails) is absent in \textit{X. maculatus} males.