What does a PCA showing two clusters labeled by ecotypes imply about gene flow?

• A. It indicates limited gene flow and adaptation to different niches.
• B. It indicates complete gene flow among all populations.
• C. It indicates no genetic differentiation between ecotypes.
• D. It indicates sampling bias.

Answer: (A)

PCA reveals patterns of genetic variation, so when individuals group into two distinct clusters that line up with ecotypes, it signals restricted gene flow between those ecotypes along with ecological differentiation. The clusters reflect different allele frequencies in the two groups, which tends to happen when migration between ecotypes is limited and selection favors different traits in their respective niches. If there were widespread gene flow, the populations would mix and the clusters would overlap rather than separate. Conversely, no differentiation would show little to no separation, and sampling bias could occasionally create patterns, but alignment with ecotypes points to real underlying structure due to limited gene flow and ecological divergence.