Why do some stickleback populations lack pelvic spines?

• A. Because pelvic spines are always disadvantageous in all aquatic environments.
• B. Because mutations in regulatory genes reduce the expression of pelvic spine development.
• C. Because sticklebacks with pelvic spines cannot survive in saltwater habitats.
• D. Because all stickleback populations are exposed to the same predators that favor spine loss.

Answer: (B)

Verified step by step guidance

1. Understand the role of pelvic spines in stickleback populations: Pelvic spines are a defensive adaptation that can protect sticklebacks from predators. However, their presence or absence can be influenced by environmental factors and genetic mutations.
2. Recognize the importance of regulatory genes: Regulatory genes control the expression of other genes, including those responsible for the development of pelvic spines. Mutations in these regulatory genes can lead to reduced or absent spine development.
3. Consider the environmental context: In some aquatic environments, the presence of pelvic spines may be disadvantageous. For example, spines can make sticklebacks more vulnerable to certain predators or impede their movement in specific habitats.
4. Evaluate the role of natural selection: In environments where pelvic spines are disadvantageous, sticklebacks with mutations that reduce spine development may have a survival advantage. Over time, these traits can become more common in the population.
5. Reject incorrect explanations: Pelvic spine loss is not due to exposure to the same predators across all populations, nor is it universally disadvantageous in all aquatic environments. Additionally, spine loss is not related to an inability to survive in saltwater habitats.