"Stickleback fish can adapt on this time scale because the species as a whole has evolved, over millions of years, a genetic bag of tricks for invading and surviving in new freshwater habitats," says Susan L. Bassham. "This hidden genetic diversity is always waiting for its chance, in the sea." Above, seawater breeding male stickleback. (Credit: Mark Currey)

Alaska

Big earthquake jolted fish into fast evolution

A 1964 earthquake in Alaska stranded seawater-native fish in newly formed freshwater ponds on islands.

In just decades, the threespine stickleback went through changes in both their genes and external traits such as eyes, shape, color, bone structure, and body armor to survive in fresh water after the earthquake, report scientists.

The earthquake—9.2 on the Richter scale and second highest ever recorded—caused geological uplift of four to five meters (13-16 feet) and captured the fish in newly formed ponds on islands in the Gulf of Alaska south of Anchorage. Researchers at the University of Oregon studies samples of stickleback gathered from these islands.

The findings, published online early in the Proceedings of the National Academy of Sciences, are important for understanding the impacts of sudden environmental change on organisms in nature, says biologist William Cresko.

“We’ve now moved the timescale of the evolution of stickleback fish to decades, and it may even be sooner than that,” Cresko says. “In some of the populations that we studied we found evidence of changes in fewer than even 10 years. For the field, it indicates that evolutionary change can happen quickly, and this likely has been happening with other organisms as well.”

Survival in a drastically changed environment is not new for stickleback, which are found throughout the Northern Hemisphere. In the journal PLOS Genetics in 2010, a team led by Cresko documented how stickleback had evolved genetically to survive in fresh water after glaciers receded 13,000 years ago. That was done with a rapid genome-sequencing technique (RAD-seq) created with collaborator Eric Johnson.

The same technology let researchers study the new samples. Genetic changes were similar to those found in the earlier study, but they had occurred in less than 50 years in multiple, separate stickleback populations. Stickleback, the researchers conclude, have evolved as a species over the long haul with regions of their genomes alternatively honed for either freshwater or marine life.

[Mass extinction let tiny fish rule the seas]

“This research perhaps opens a window on how climate change could affect all kinds of species,” says Susan L. Bassham, a senior research associate in Cresko’s lab and coauthor of the 2010 paper. “What we’ve shown here is that organisms—even vertebrates, with long generation times—can respond very fast to environmental change.

“And this is not just a plastic change, like becoming tan in the sun; the genome itself is being rapidly reshaped,” she says. “Stickleback fish can adapt on this time scale because the species as a whole has evolved, over millions of years, a genetic bag of tricks for invading and surviving in new freshwater habitats. This hidden genetic diversity is always waiting for its chance, in the sea.”

The National Science Foundation funded the work. Coauthors of the new study are from the University of Alaska and the University of Illinois at Urbana-Champaign.

Source: University of Oregon

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