Question

part a
how did some stickleback populations come to live exclusively in fresh water?
stickleback populations swam to freshwater lakes to spawn and stayed because there were no predators.
sticklebacks developed traits that made them better adapted to fresh water and, as a result, they moved to a freshwater environment.
some stickleback populations became trapped in lakes that formed at the end of the last ice age.
the ancestors of freshwater sticklebacks are marine stickleback species that lived primarily in the ocean and migrated to freshwater to spawn.

Explanation:

Stickleback populations became trapped in lakes formed at the end of the last ice age. Their ancestors were marine sticklebacks that migrated to freshwater to spawn. Over time, some stickleback populations developed traits that made them better adapted to fresh water. As a result, they moved to a freshwater environment and stayed because there were no predators.

Answer:

Stickleback populations became trapped in lakes formed at the end of the last ice age. Their ancestors were marine sticklebacks that migrated to freshwater to spawn. Over time, some stickleback populations developed traits that made them better adapted to fresh water. As a result, they moved to a freshwater environment and stayed because there were no predators.