What is the role of pelvic spines in stickleback populations with respect to predation?

• A. They help the stickleback swim faster.
• B. They are used for mating displays.
• C. They store calcium.
• D. They provide an effective defense against large predatory fish.

Answer: (D)

Antipredator defenses can evolve when predators exert strong pressure. Pelvic spines in sticklebacks act as a physical barrier that makes it harder for large predatory fish to grab, bite, or swallow them. In populations that face more threats from big fish, longer or more pronounced spines tend to improve survival, so those traits are favored. Conversely, in environments with fewer large predators, spines may be reduced because maintaining them can trade off with growth or mobility. This is why the role of pelvic spines is to deter or hinder predation by large fish, not to improve swimming speed, attract mates, or store calcium.