Bear Paw Lake and Frog Lake were likely populated by the same sea-run population of stickleback at the end of the last ice age. Which of the following statements is the most reasonable explanation for what might have happened to the stickleback in each lake since colonization? Question 4 options:

Over many generations, stickleback in Bear Paw Lake have lost their pelvic spines, while those in Frog Lake have retained full pelvises.

Over many generations the pelvic structures in Bear Paw Lake stickleback have remained the same, and the stickleback in Frog Lake have gained their pelvic spines.

Stickleback in Frog Lake will lose their pelvic spines before the next ice age.

The ancestral marine population of stickleback must have lacked pelvic spines.