Well, not exactly. From ScienceDaily:
Steelhead trout, a member of the salmon family that live and grow in the Pacific Ocean, genetically adapted to the freshwater environment of Lake Michigan in less than 120 years.
Steelhead were intentionally introduced into Lake Michigan in the late 1800s in order to bolster recreational and commercial fisheries. In their native range, which extends from California to Russia, steelhead hatch in freshwater rivers, migrate to the ocean, and return to freshwater to spawn. This migration allows steelhead to feed in the ocean, where they can grow larger and produce more eggs than if they remained in freshwater streams for their entire lives.
The steelhead introduced into Lake Michigan continue to spawn in small freshwater tributaries and streams, but now treat the entirely freshwater habitat of the Great Lakes as a surrogate ocean. After their introduction into Lake Michigan, steelhead began to naturally reproduce and established self-sustaining populations throughout the Great Lakes. To examine how these fish adapted to this novel environment, a team led by Mark Christie, an assistant professor of biological sciences at Purdue University, sequenced the complete genomes of 264 fish. The team then compared steelhead from Lake Michigan to those from their ancestral range, searching for outlier regions associated with genetic adaptation.
The research, which was published in in the journal Molecular Ecology, found that regions of three chromosomes in steelhead evolved after they were introduced in Lake Michigan, offering insight into how this ocean-migrating fish adapted to an entirely freshwater environment. Paper. (paywall) – Janna R Willoughby, Avril M Harder, Jacob A Tennessen, Kim T Scribner, Mark R Christie. Rapid genetic adaptation to a novel environment despite a genome-wide reduction in genetic diversity. Molecular Ecology, 2018; DOI: 10.1111/mec.14726 More.
In short, in their original habitat, the trout were spawned in fresh water, lived in salt water, and – as adults – returned to fresh water to spawn. But having no salt water available in the new habitat, they have adapted to lifelong freshwater living. It’s a good find but these fish were already capable of living in both environments. It’s not as if they moved from lifelong salt water to lifelong fresh water.
From Elizabeth Pennisi at Science:
Although we tend to think of evolution as happening over thousands, if not millions, of years, critical changes can take little more than a century. That’s what happened with a group of steelhead trout transplanted from the salty seas of California to the fresh waters of Lake Michigan for game fishermen in the 1890s. A new study shows that the fish, which typically live part of their lives in the ocean like salmon, developed key genetic differences that allowed it to live wholly in freshwater—in little more than 100 years.
The discovery shows how quickly organisms can adapt to a new lifestyle—if they have some of the right genes to start with, says Michael Blouin, a geneticist at Oregon State University in Corvallis. “The work is a nice example” of how evolution can happen “over very short time periods.”More.
A friend writes to point out, “Here is the key phrase in the article, ‘The discovery shows how quickly organisms can adapt to a new lifestyle—if they have some of the right genes to start with,’ with emphasis on ‘right genes to start with.’ That’s important when considering claims about evolution.”
If some of the fish were returned to the Pacific coast, would they then go back to their original lifestyle within a century or so? Too bad no one person will live to find that out but it might be worth testing. For one thing, how do we know that the genetic change took over a century? Genome mapping wasn’t available thirty years ago. Maybe this is something they can do in a few generations. After all, blind cave fish were bred to see again.
See also: A Tunable Mechanism Determines the Duration of the Transgenerational Adaptations
Devolution: Getting back to the simple life