"Evolution in Fast Forward": Novel NE CASC Study Yields Surprising Findings Regarding Invasive Fish Management

A new publication led by former NE CASC Research Fellow Liam Zarri reveals important and unexpected lessons about invasive species management. Decades of invasive smallmouth bass removal from the Adirondacks resulted in a novel discovery of rapid evolution. Despite the absence of a clear physiological adaptation pathway, intensive manual removal produced a larger population of the invasive predatory fish, growing faster and maturing earlier. The article was recently published in the Proceedings of the National Academy of Science, and a video about this project is available on YouTube. 

“Even though we hadn’t intended it, in fact we set up the perfect evolutionary experiment,” says NE CASC researcher and senior author, Pete McIntyre.

“Humans are driving changes in the natural environment, and there are evolutionary consequences of those changes everywhere. In the case of invasive species, you’re dealing with the species that are most talented,” says McIntyre. “They’re sort of the ecological chameleons,” he adds.

“Smallmouth bass were first brought up into the Adirondacks well over a century ago. Now fast forward to today, we recognize that smallmouth bass is actually a very vigorous predator,” says McIntyre.

“Pound for pound, they’re one of the hardest fighting fish out there. And because of that, they have been introduced all across North America, far beyond their original range,” says first author Liam Zarri, who led the study as an NE CASC Fellow and now is a Postdoctoral Fellow at the Smithsonian Institution.

Pete describes the Adirondacks invasion as a “double whammy scenario.” On one hand, climate change is already compressing habitat for cold-dwelling native brook trout and lake trout, with warming surface waters and little to no oxygen at the lake bottom. McIntyre adds, “then if you overlay smallmouth bass as abundant and vigorous competitors and even predators on young trout, it becomes a very challenging situation.”

“Usually, we don’t have the opportunity to attempt control efforts for invasive species year after year after year across decades,” says McIntyre.

Zarri says, “Invasive species removal efforts should be envisioned as an evolutionary arms race. Pests, insects, can evolve a physiological resistance to pesticides, but with invasive fishes, we use measures such as netting, or in this case electrofishing, which don’t have quite the same very clear physiological pathway that allows evolution to happen.”

“We wanted to try and understand why our eradication effort was failing, and it turns out that it was failing not because the fish evolved to resist our removal effort, but they underwent life history evolution,” says Liam Zarri. The team discovered a trio of traits that gave bass an advantage. They unintentionally selected for individuals that grow faster, mature earlier, and invest more in reproduction.

McIntyre explains, “It was evolution in fast forward. We set up a set of rules for control, and then we execute that script year after year. It makes sense from our perspective, but as a byproduct of that predictability, that’s how you drive evolution.” The reason this has massive implications for invasive species management, according to Pete is that “we have no idea how widespread evolutionary responses to control measures may be and how that could enhance the persistence and spread of introduced species.”

“And so, the lesson there is that we don’t want these introductions to turn into ecologically damaging invasions… We have to take smart measures to prevent the species from getting there in the first place,” McIntyre concludes.

Funding for this project was provided by the Adirondack League Club, the Northeast Climate Adaptation Science Center, the National Science Foundation Extreme Science and Engineering Discovery Environment, the Cornell University Elizabeth Miller Francis ’47 Summer Research Grant, and the Cornell University Kieckhefer Adirondack Fellowship.