Using fish bred at Washington State University, an international team of researchers has mapped the genetic¹ profile of the rainbow trout², a versatile³ salmonid whose relatively⁵ recent genetic history opens a window into how vertebrates evolve. The 30-person team, led by Yann Guiguen of the French National Institute for Agricultural Research, reports its findings this week in Nature Communications.

 

The investigators⁶ focused on the rate at which genes⁷ have evolved since a rare genome doubling event occurred in the rainbow trout approximately 100 million years ago. Unlike most evolutionary⁸ processes involving mutations and the selection of advantageous⁹ traits, a doubling event acts like the copied draft of a piece of writing that can be edited and recast without the risk of destroying the earlier version.

 

Ordinarily, the consequences of such doubling events are lost to science as they get cast out as a result of genetic changes in subsequent generations. But because 100 million years is a relatively short time for doubling events, the trout researchers could in effect glimpse the fish's evolutionary editing process.

 

"In humans and most vertebrates the duplication events were older so there are fewer duplicated genes still present," said Gary Thorgaard, a co-author and WSU biologist with four decades of experience peering into the trout's genes. "Most of the duplicated genes get lost or modified so much that they are no longer recognizable as duplicates over time. In the trout and salmon⁴ we can see an earlier stage in the process and many duplicated genes are still present. "

 

The rainbow trout, Oncorhynchus mykiss, is one of life's great success stories. It has straddled the worlds of nature and nurture¹⁰, naturally thriving in a range of temperatures and water quality while responding to domestication¹¹ so well that it has been spread by human hand from the Pacific Rim¹² to thrive in waters on six continents.

 

In Washington alone, state hatchery crews have stocked more than 16 million fish in lakes. The lowland-lake trout-fishing season opener, which takes place this year on April 26, draws some 300,000 people, making it the state's most popular outdoor sporting event.

 

Thorgaard, the only American on the largely French research team, provided genetic material from the Swanson line of rainbow trout. Originally from Alaska's Kenai Peninsula, the fish has been cloned at WSU, ensuring that researchers are looking at the same fish in successive studies and simplifying interpretation¹³ of its sequenced genes.

 

"Several studies had previously¹⁴ been done on the Swanson clonal line," said Thorgaard, "which helped in producing and interpreting the genome sequence in this study."

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