Evolution Shocks Scientists in an Electric Battle against Invasive Bass

By Martin J. Kernan edited by Sarah Lewin Frasier

A group of Cornell University scientists have been outmaneuvered by a formidable (and genetically supercharged) adversary: the smallmouth bass of Little Moose Lake in New York State’s Adirondack Mountains.

The invasive—and drastically overpopulating—species prevailed over the scientists’ 20-year electric culling campaign by evolving to grow faster and spawn younger. This strategy let them reproduce before the scientists’ specially equipped boat took its twice-yearly lake cruise, electrically stunning all fish within several feet so the team could toss the bass into a cooler. (The other fish species were left to recover.) The lake’s bass population is now thriving in greater numbers than ever.

Smallmouth bass are among the hardest-fighting freshwater sport fishes, popular with anglers for the leaping acrobatics the fish perform trying to unhook themselves. In the late 1800s outdoor enthusiasts started introducing this adaptable, red-eyed predator into countless lakes and fishing holes, where it can often outcompete locals—including prized trout—for prey.

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Little Moose’s native lake trout once grew to a whopping 35 pounds and could span three feet in length, but now the fully mature trout “are only nine inches long. They’re just totally stunted, and they’re not catchable by anglers,” says Liam Zarri, a molecular ecologist at the Smithsonian National Zoo and Conservation Biology Institute. While at Cornell, he identified the genetic effects of the attempted eradication and recently published the findings in the Proceedings of the National Academy of Sciences USA.

This bass species had the genes for a range of survival strategies before the culls started, Zarri says. But individual bass that were genetically predisposed to sexually mature relatively late and grow slowly into big, old, lake-dominating specimens didn’t survive the shock treatments. This left only “the individuals that live fast, die young—the all-out-motorcycle-riding smallmouth bass that reproduce as early as they can because they’re probably not going to make it to the next year,” he says.

Driving the species’ new life in the fast lane are chromosomes involved with growth rate and reproduction timing, Zarri explains. DNA sequences in these chromosomes are “wildly different,” he says, from those in tissue samples taken from Little Moose bass preserved before the electrofishing began. The changes spread through the population and culminated in an evolutionary backlash, “but the lesson isn’t about victory or defeat,” says Cornell geneticist Nina Therkilsden, who helped Zarri compare the genomes. “It’s about the need for conservation strategies that anticipate and work with evolution rather than against it.”

Stephanie Green, an ecologist who grapples with invasive species in Canada and wasn’t involved in the Cornell research, says varying the culls’ timing and frequency could make them less likely to fuel the rapid evolution—and the Cornell scientists say they’re actively considering such alternatives.

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