Which factor is least relevant to explaining rapid, repeated armor reduction across freshwater stickleback populations?

Which factor is least relevant to explaining rapid, repeated armor reduction across freshwater stickleback populations?

• A. Variation in predator communities
• B. Energy trade-offs of armor
• C. Standing genetic variation at multiple loci
• D. Within-lake random mating patterns

Answer: (D)

Rapid, repeated armor reduction in freshwater sticklebacks shows how similar environments shape evolution in parallel ways. The most relevant forces here are ecological selection and the genetic groundwork that makes adaptation fast. Variation in predator communities matters because the kinds and strengths of predators differ among lakes. In freshwater, some lakes have fewer or different predators than the marine ancestors, so the protective benefit of heavy armor is reduced. That shifts the balance toward lighter armor. Energy trade-offs are central too. Heavier armor increases body mass, which raises energy costs and can impede swimming and foraging. If the ecological payoff of maintaining heavy armor drops, natural selection favors reduced armor to boost growth and reproductive success. Standing genetic variation at multiple loci is key for rapid, repeated changes. When there’s existing genetic variation affecting armor at many genes, populations can shift phenotype quickly in response to new selective pressures, producing the parallel pattern observed across lakes. Within-lake random mating patterns, by themselves, don’t explain why many lakes show the same armor reduction. Mating within a lake influences local allele frequencies, but the repeated cross-lake pattern is best explained by shared selection pressures and the available genetic variation rather than how individuals mate within a single lake.

Rapid, repeated armor reduction in freshwater sticklebacks shows how similar environments shape evolution in parallel ways. The most relevant forces here are ecological selection and the genetic groundwork that makes adaptation fast.

Variation in predator communities matters because the kinds and strengths of predators differ among lakes. In freshwater, some lakes have fewer or different predators than the marine ancestors, so the protective benefit of heavy armor is reduced. That shifts the balance toward lighter armor.

Energy trade-offs are central too. Heavier armor increases body mass, which raises energy costs and can impede swimming and foraging. If the ecological payoff of maintaining heavy armor drops, natural selection favors reduced armor to boost growth and reproductive success.

Standing genetic variation at multiple loci is key for rapid, repeated changes. When there’s existing genetic variation affecting armor at many genes, populations can shift phenotype quickly in response to new selective pressures, producing the parallel pattern observed across lakes.

Within-lake random mating patterns, by themselves, don’t explain why many lakes show the same armor reduction. Mating within a lake influences local allele frequencies, but the repeated cross-lake pattern is best explained by shared selection pressures and the available genetic variation rather than how individuals mate within a single lake.