What does FST measure in stickleback population comparisons?

• A. FST measures ecological niche overlap between populations.
• B. FST measures metabolic rate differences.
• C. FST is a measure of genetic differentiation between populations; high values indicate substantial differentiation, signaling local adaptation or restricted gene flow.
• D. FST measures gene expression levels.

Answer: (C)

FST is a statistic that captures how different populations are at the genetic level by comparing how common different alleles are across populations. In sticklebacks, populations in different environments (like marine versus freshwater) can become genetically distinct because gene flow between them is limited and natural selection acts in different directions. So when FST is high, it means there’s substantial genetic differentiation between the populations, which often points to local adaptation or restricted gene flow. FST doesn’t measure ecological niche overlap, metabolic rate, or gene expression levels—those are about phenotypes or molecular activity, not patterns of allele frequencies across populations.