[env-trinity] CBB: Study: Changes to Genetics of Hatchery Steelhead Occur in Just One Generation

[Sari Sommarstrom]

THE COLUMBIA BASIN BULLETIN: Weekly Fish and Wildlife News

www.cbbulletin.com

February 26, 2016            Issue No. 782

 

Study: Changes To Genetics Of Hatchery Steelhead Occur In Just One
Generation

 

It takes just one generation for the DNA of steelhead domesticated in
hatcheries to be altered and to be significantly different than steelhead
whose parents are wild, according to a recent study by Oregon State
University.

 

In fact the study found that in just one generation there were 723 genes
that differed between the offspring of wild steelhead and the offspring of
first-generation hatchery steelhead.

 

Further, the study found through gene enrichment analysis that adapting to
the hatchery environment involves responses by the steelhead in wound
healing, immunity and metabolism, suggesting the adaptation is due to
crowding in hatcheries. 

 

"We found hundreds of genes were expressed differently between the offspring
of first-generation hatchery fish and the offspring of wild fish, and that
the difference was heritable from their parents," said lead researcher
Michael Blouin, professor in the Department of Integrative Biology at OSU.

 

Although over 700 genes are just a small fraction of the total number of
genes in the genome, Blouin said it is a surprisingly high number to show a
difference after just one generation of selection.

 

The results show that hatchery fish can be genetically different from wild
fish after only a generation of selection in a hatchery, he said, and "more
importantly, it allows us to generate hypotheses about what types of traits
are under selection in hatcheries." 

 

"For example," he continued, "the fact that many of the differentially
expressed genes are involved in immune-related functions, such as wound
repair, suggests the hypothesis that hatchery fish might be selected for
their ability to tolerate injuries. This is actually consistent with the
idea that crowding is a selective factor, given juvenile steelhead can be
pretty aggressive with each other in captivity." 

 

Blouin cautioned that the hypothesis still needs to be tested, "but data
such as these may eventually lead us to the traits under selection, and thus
to ideas on how we might want to modify hatchery culture practices."

 

The study, "A single generation of domestication heritably alters the
expression of hundreds of genes," was published online February 17, 2016, in
the journal Nature Communications,
http://www.nature.com/ncomms/2016/160217/ncomms10676/full/ncomms10676.html.

The article is open access and is free to download.

 

In addition to Blouin, co-authors are Mark Christie, a post-doctoral student
at OSU at the time of the study and now an assistant professor at Purdue
University; Melanie Marine, research assistant at OSU; Samuel Fox, a
post-doctoral student at OSU at the time of the study and now an assistant
professor at St. Martin's University; and Rod French, district fish
biologist, Lower Columbia River, at the Oregon Department of Fish and
Wildlife.

 

According to the study, steelhead is one of the few fish species considered
to have been fully domesticated and the responses to selection routinely
occur in steelhead within less than ten generations of captive breeding.
This is the first study to demonstrate that the earliest stages of
domestication are characterized by large changes in heritable patterns of
gene expression. 

 

"We hypothesize that adaptation to crowded conditions may drive much of this
early domestication. Regardless of the mechanism, it is remarkable that a
single generation of domestication can translate into heritable differences
in expression at hundreds of genes," the study says.

 

This is the second study about crowding in hatcheries and the domestication
of hatchery steelhead Blouin and others have published recently. "The
effects of high rearing density on the potential for domestication selection
in hatchery culture of steelhead (Oncorhynchus mykiss)," was published
online August 5, 2015, in the Canadian Journal of Aquatic Sciences
(http://www.nrcresearchpress.com/doi/abs/10.1139/cjfas-2015-0233#.VjEBjberTI
U.)

 

(See CBB, October 30, 2015, "Study Looks At Whether Crowded Hatcheries Push
Steelhead To Domestication, Small Body Size,"
http://www.cbbulletin.com/435426.aspx)

 

Blouin said the overall goals of the two studies are similar.

 

"Substantial evidence suggests that salmonid fish rapidly adapt to
hatcheries in ways that make them less fit in the wild," he said. "But we
don't know what traits are under selection in the hatcheries or what
environmental conditions of the hatchery cause such strong selection
pressures."

 

He added that the goal of his research is to answer those two questions -
what traits and what conditions - to discover ways to modify hatchery
rearing practices in order to reduce the selection pressures, thereby
producing hatchery fish that are more like wild fish.

 

The first study, he said, was to test a hypothesis about how crowding can
increase the rate of domestication, while this more recent study looks at
DNA level changes after selection "in order to generate hypotheses about
what traits might be responding to selection."

 

"Our goal here is not to bash hatcheries," Blouin said. "Our goal is to
figure out how to improve them. If one could modify hatchery practices in
order to produce hatchery fish that are more like wild fish, then that would
reduce concerns about genetic impacts of hatchery fish on wild populations."

 

The modification could be as simple as changing the way hatchery fish are
fed or housed, or it may be that the goal of making hatchery fish more like
wild fish is not feasible. "We won't know until researchers tackle the
question," Blouin said.

 

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