After Alaskan Earthquake, Threespine Sticklebacks Quickly Evolved For Freshwater

By on December 15, 2015
Threespine stickleback in a University of Oregon lab that have evolved to live in freshwater. (Credit: University of Oregon)

After an earthquake hit Alaska in 1964, several islands throughout the Gulf of Alaska were lifted up by many meters. This meant that some of the marine life living in the saltwater of the Gulf were very quickly tasked with finding ways to survive in the new and challenging freshwater ponds formed on the islands.

One of these lifeforms was the threespine stickleback, a tiny fish species that was believed to have evolved over millennia to survive in marine waters. With an eye for challenging this notion, researchers at the University of Oregon have dived into the evolution dynamics of sticklebacks to see if they really do need thousands of years to change.

To come at the question, scientists at the university gathered some of the threespine sticklebacks living in the island ponds and took them back to their lab for analysis. The quake’s timing provided them with an excellent opportunity to assess how quickly the sticklebacks had changed physiologically over a relatively short time period, from 1964 to present.

The researchers opted to use rapid genome sequencing technology to gauge the changes. By using this approach, the U. of Oregon scientists could compare their findings to those from past investigations that also used rapid genome sequencing, including one that looked at the rates at which sticklebacks evolved after glaciers receded in Alaska about 13,000 years ago.

Sticklebacks from three islands were considered in the study, in addition to other sticklebacks gathered from the ocean waters surrounding them.

A male threespine stickleback that lives in saltwater. (Credit: Mark Currey / University of Oregon)

A male threespine stickleback that lives in saltwater. (Credit: Mark Currey / University of Oregon)

By comparing the oceanic sticklebacks with their freshwater descendants, researchers easily noted how much the two types of fish had diverged physiologically. From there, they checked to see how the changes stacked up with those registered over thousands of years in the receding glacier study.

Researchers saw that, just in the short time since the 1964 earthquake (relative to millennia), the phenotypes of freshwater threespine sticklebacks on the three islands have diverged greatly from sticklebacks living in saltwater. The results support the idea that the freshwater populations of the fish have evolved repeatedly over just the last half-century to become more suited to their new living situations.

In addition, the scientists concluded that sticklebacks have likely evolved over the long term to have different parts of their genome suited for freshwater or saltwater living, depending on their needs. That helps to explain how the fish could rapidly adjust to living in the freshwater pools so quickly.

Such rapid evolution may not only be capable by sticklebacks, researchers say, and they expect that their results will help spur new questions into the area of evolution over short timescales. After all, there have been many other animals that have had to adjust to sudden shifts in their environments before.

Full results of the study, including more on methods and implications, are published in Proceedings of the National Academy of Sciences.

Top image: Threespine stickleback in a University of Oregon lab that have evolved to live in freshwater. (Credit: University of Oregon)

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