What does parallel evolution mean in sticklebacks, and give an example regarding armor plating?

• A. Independent populations evolving similar traits under similar selective pressures; freshwater populations repeatedly evolve reduced armor across lakes.
• B. A single population influences another's evolution
• C. Parallel evolution requires identical genes in all populations
• D. It never occurs in sticklebacks

Answer: (A)

Parallel evolution is when separate populations facing similar selective pressures independently arrive at the same or very similar trait changes. In sticklebacks, many freshwater populations across different lakes repeatedly evolve reduced armor plating as they adapt to the freshwater environment. The lighter plating helps them save energy and may be favored when predators differ or are less intense in lakes, leading each population to converge on the same outcome through independent evolutionary paths. It’s also worth noting that parallel evolution doesn’t require identical genetic changes in every population; different genetic routes can produce the same reduced-armor phenotype, though sometimes the same gene (like EDA) is involved.