When Hybrids Go Wild

By John Upton

Q: How do you make a hybrid trout go wild?

A: You wait.

From a survival-of-the-fittest perspective, a domesticated animal is a poor facsimile of its wild relative. That’s why a salmon or a trout reared in a hatchery is less likely to survive in the ocean and return safely to its home river come spawning time.

When domesticated creatures are mixed with a population of wild ones, such as through fish-stocking programs, their domesticated genes, many of which are ill-suited to the idiosyncrasies of the new environment, can be passed on to the next wild-dwelling generation. The genetic contamination lingers so long in the newly hybridized population that wildlife management policies generally consider it to be permanent.

The good news for a hybrid-wearied world is that recent research suggests that a wild trout population’s newly-hybridized traits could be shed quickly — even if some of the hybrid DNA sticks around.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

Ontario and Concordia University researchers reared brook trout from two hybridized populations and from one wild population in Ontario’s Algonquin Park. They also obtained trout from a nearby hatchery. The four populations were mixed equally in holding tanks, then released into three small, hitherto trout-free lakes in the North Shore region of Lake Huron.

The researchers sampled from the three lakes five months later, testing how well each of the strains had survived the rigors of the new environment. By then, most of the fish had died, which is normal after brook trout are planted

in Ontario waters. Mortality in one of the lakes was 96 percent. In the other two lakes: 80 percent. The scientists found that members of the hybrid and wild populations had similar chances of survival — and that they all fared better than their hatchery cousins.

One of the hybrid populations studied had last been contaminated with hatchery fish some five generations earlier. The other had been hybridized for 11 generations.  The results, the scientists wrote in a paper published recently in Evolutionary Applications, “suggest that within five to eleven generations, selection can remove introduced foreign genes from wild populations.”

The findings are a reminder of the fast pace at which evolution is capable of working.

“Allowing natural selection to act for relatively few generations can produce hybridized populations that closely resemble nearby non-hybridized populations — both physically and ecologically,” said Concordia University’s Andrew Harbicht, one of the researchers behind the study.

“Certain genetic vestiges will persist into the future over the long term. But, generally, the hybrids will behave ecologically similarly to their wild predecessors after a fairly short time period,” Harbicht said.