Questions 14-17
Stickleback fish are found in both marine and freshwater habitats. The marine fish have no scales but have
hardened, armorlike plates along their sides. The plates are thought to protect sticklebacks from certain predators.
In the late 1980s, sticklebacks from a marine population colonized Loberg Lake, a freshwater lake in Alaska.
Starting in 1990, researchers sampled fish from the lake every four years and recorded the armor-plate phenotypes of
the male sticklebacks in each sample. The armor-plate phenotypes were categorized as either complete (plates
extending from head to tail), partial (plates extending from head to abdomen), or low (a few plates near the head
only). The results are shown in the table below.