For my PhD thesis, I explored the process of ecological speciation, with a goal of resolving to what extent natural selection plays a deterministic role in this phenomenon. A particular kind of evolution, where populations evolve similar traits in response to similar environments (called parallel evolution because the trait trajectories of both populations are parallel to one another), can be a powerful way to demonstrate that selection is, indeed, deterministic. To study this, I used the threespine stickleback (Gasterosteus aculeatus), a small fish that has repeatedly invaded freshwater environments from an ocean source after the last ice age about 10,000 years ago. This species demonstrates parallel evolution in several traits that allowed it to adapt to life in lakes vs. streams. Most of my work was done on Vancouver Island where several of these lake-stream pairs exist.