A population of pink salmon (Oncorhynchus gorbuscha) that spawns in a stream near Juneau, Alaska, has evolved genetic changes over the last 3 decades that allow the fish to spawn earlier in the year, according to a new study published in the Proceedings of the Royal Society B yesterday (July 11). The genetic shift may have occurred over as little as two generations and, if confirmed through other studies, may provide the first evidence of microevolution in response to the current change in global climate.

“It has been extremely difficult to determine whether any of the multitudes of observed phenological changes in nature are due to rapid microevolution within a population," Ryan Kovach, the population ecologist at the University of Alaska in Fairbanks who led the study, told Nature. “This study is the first empirical example using genetic data to confirm this theory, and so addresses a...

The salmon population that Kovach studied has been migrating upstream to spawn 2 weeks earlier than they did 40 years ago—a trend also observed in other salmon populations. To confirm whether there was a genetic basis to this change in behavior, Kovach and his team monitored the frequency of a genetic marker that had been bred into late-migrating fish during the 1980s. They found that the frequency of this marker had dropped by 20 percent by 2011—then accounting for only 10 percent of the population.

Although the genetic change seems to have made the spawning salmon better adapted to the warming temperatures of the waters—which have risen by 1 degree Celsius since the 1980s—it is still unclear whether this shift in behavior negatively affects the survival of the salmon at other stages of their lives, particularly when the juveniles head out to sea. “Opposing selection in different life stages is a serious concern with climate change,” Lisa Crozier, a fish ecologist at the Northwest Fisheries Science Center in Seattle, Washington, told Nature.

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