Which factor drives rapid, repeated, and predictable phenotypic divergence in stickleback adaptive radiation?

Which factor drives rapid, repeated, and predictable phenotypic divergence in stickleback adaptive radiation?

• A. Ecological opportunity
• B. Genetic drift
• C. Founder effects
• D. Random mutation

Answer: (A)

Ecological opportunity drives this pattern. When sticklebacks colonize freshwater environments, they encounter new resources, different predators, and less competition, creating strong, consistent selective pressures. Those pressures favor similar trait changes across independent populations—like evolving lighter armor, different body shapes, or altered gill raker configurations to exploit available food niches. Because the ecological challenges are similar in each setting, evolution proceeds in a repeatable way, producing rapid and predictable phenotypic divergence. Genetic drift, founder effects, and random mutations can cause changes, but they are random and unlikely to produce the same, directional patterns across many populations in the same way ecological opportunity does.

Ecological opportunity drives this pattern. When sticklebacks colonize freshwater environments, they encounter new resources, different predators, and less competition, creating strong, consistent selective pressures. Those pressures favor similar trait changes across independent populations—like evolving lighter armor, different body shapes, or altered gill raker configurations to exploit available food niches. Because the ecological challenges are similar in each setting, evolution proceeds in a repeatable way, producing rapid and predictable phenotypic divergence.

Genetic drift, founder effects, and random mutations can cause changes, but they are random and unlikely to produce the same, directional patterns across many populations in the same way ecological opportunity does.