Two populations of a species of pine tree are located on opposite sides of a mountain range. The two populations are genetically similar to each other. An invasive beetle infestation kills 80% of the trees on the west side of the range. The beetle population does not spread to the eastern side of the range, and the east tree population does not experience any beetle-related loss. After the infestation, the western tree population increases in size again.

Which of the following is the expected outcome of genetic testing comparing the two populations?