rainbow faces cut-throat competition

Montana’s Flathead Basin has long been a spawning haven for the westslope cutthroat trout. But as waters in the region warm, rainbow trout have swum up from the western lakes where they were introduced decades ago to cutthroat native grounds.

As rainbow trout meet and interbreed with dwindling cutthroat trout populations, the survival of cutthroat trout is at risk. Instead, a hybrid species is taking its place.

“It’s a major cause of species extinction—lots of species are now disappearing because they are being genetically swamped by other, commoner ones,” said Stuart Pimm, a professor of conservation ecology at Duke University.

In some cases, hybridization can lead to reduced genetic diversity in animals, according to David Tallmon, an associate professor of biology at the University of Alaska. “Rather than growing a new branch on the [genetic] tree, you have two branches growing together,” he said.

In the case of cutthroat-rainbow trout hybrids, the hybrids are less genetically fit, with offspring of the hybrids struggling to survive, a study led by researchers from the U.S. Geological Survey found.

Scientific American, 1 Jun 2015