Evolution is normally considered a process that takes generations, if not thousands of years, but a recent study has shown that it can occur within the span of a single generation.
Studying steelhead trout (Onchorhynchus mykiss) in Oregon's Hood River for 19 years, Mark Christie and his colleagues showed in their genetic analysis that first-generation captive-reared trout raised in hatcheries had significantly lower survival and reproductive rates when reintroduced into the wild. In fact, the more successful the fish were at surviving hatchery conditions, the worse they fared when returned to the wild.
This study shows that hatcheries can exert a profound influence on the genetic makeup of salmon populations, allowing for the selection within a single generation of traits that would confer advantages in hatcheries at the cost of the ability to thrive and reproduce in the wild.
It was not immediately clear the exact traits that were being selected for that were disadvantageous to the hatchery fish, but the authors postulate from previous studies that growth rate, egg size, fecundity, physiological processes associated with smoltification, and behaviours may be involved.
According to lead author Mark Christe, "We expected to see some of these changes after multiple generations. To see these changes happen in a single generation was amazing. Evolutionary change doesn't always take thousands of years."
The paper is published in the Proceedings of the National Academy of Sciences.
For more information, see the paper: Christie, MR, ML Marine, RA French and MS Blouin (2012) Genetic adaptation to captivity can occur in a single generation. Proceedings of the National Academy of Sciences of the United States of America 109, pp. 238–242.
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