Humans sped up evolution in a Canadian lake. How did this happen?

FEBRUARY 24, 2016

by Susanna Pilny

The accidental introduction of crayfish into a lake in British Columbia, Canada, by humans has caused the extinction of two species of fish that had lived there for some 15,000 years—well, sort of.

Life, ah…finds a way, and what has replaced these two fish could have dire consequences for the local environment.

The two fish were similar species of endangered threespine stickleback fish, both of which coexisted peacefully in Enos Lake in BC—until they didn’t.

"When two similar species are in one environment, they often perform different ecological roles," said co-author Seth Rudman, a PhD student in zoology at UBC, in a statement. "When they go extinct, it has strong consequences for the ecosystem."

In the case of Enos Lake, one species tended to live in the middle of the lake, where it preyed on zooplankton, while the other lived nearer to the shore and ate mostly waterborne insect larvae. They more or less left each other alone, breeding only with their own species, for thousands of years.

But then, in the early 1990s, American signal crayfish were accidentally introduced to the lake, likely through fishermen who were using them as bait on Vancouver Island.

From then on, the crayfish began to clear-cut the vegetation on the bottom of the lake—forcing the middle-of-the-lake sticklebacks to search for food and mates in the open water above, where the shore-preferring species lived.

Forced together, these two species of fish began to interbreed between 1994 and 1997—and then totally disappeared, leaving behind only a hybrid species of stickleback.

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