Which statement supports the involvement of standing genetic variation in rapid armor reduction across lakes?

Which statement supports the involvement of standing genetic variation in rapid armor reduction across lakes?

• A. Standing variation can explain rapid adaptation across lakes
• B. Armor reduction occurs only after new mutations
• C. No standing variation observed
• D. Armor reduction is due to learning

Answer: (C)

Standing genetic variation is the pool of alleles already present in a population before a change in the environment. When different lakes present similar selective pressures, alleles that reduce armor can already exist in some individuals. Natural selection can quickly favor those pre‑existing alleles, so armor reduction can spread rapidly across lake populations without waiting for new mutations. That quick, parallel response across multiple lakes is the hallmark of adaptation driven by standing variation, making the statement that standing variation can explain rapid adaptation across lakes the best support for its involvement. The other ideas don’t fit as well: relying on new mutations would slow adaptation and isn’t about the existing genetic reservoir; saying there’s no standing variation contradicts the mechanism of rapid, repeated changes; attributing armor reduction to learning describes a non-genetic, plastic change rather than inherited variation.

Standing genetic variation is the pool of alleles already present in a population before a change in the environment. When different lakes present similar selective pressures, alleles that reduce armor can already exist in some individuals. Natural selection can quickly favor those pre‑existing alleles, so armor reduction can spread rapidly across lake populations without waiting for new mutations. That quick, parallel response across multiple lakes is the hallmark of adaptation driven by standing variation, making the statement that standing variation can explain rapid adaptation across lakes the best support for its involvement.

The other ideas don’t fit as well: relying on new mutations would slow adaptation and isn’t about the existing genetic reservoir; saying there’s no standing variation contradicts the mechanism of rapid, repeated changes; attributing armor reduction to learning describes a non-genetic, plastic change rather than inherited variation.