Re: Researchers document rapid, dramatic 'reverse evolution' in the threespine stickleback fish

This might be a good example of histone-coded environmental influences (or,
IOW, of environmental effects on the epigenome).
"Robert Karl Stonjek" <rstonjek@xxxxxxxxxxxxxx> wrote in message
news:g0khkc$5os$1@xxxxxxxxxxxxxxxxxxxxxx
Researchers document rapid, dramatic 'reverse evolution' in the threespine
stickleback fish

[moderator's note: There's a pretty good comparison pair of photos
in one of our daily papers if you want to look; here's the link:

http://seattlepi.nwsource.com/local/363263_oddfish16.html

Enjoy. - JAH]


Evolution is supposed to inch forward over eons, but sometimes, at least
in
the case of a little fish called the threespine stickleback, the process
can
go in relative warp-speed reverse, according to a study led by researchers
at Fred Hutchinson Cancer Research Center and published online ahead of
print in the May 20 issue of Current Biology (Cell Press).

"There are not many documented examples of reverse evolution in nature,"
said senior author Catherine "Katie" Peichel, Ph.D., "but perhaps that's
just because people haven't really looked."

Peichel and colleagues turned their gaze to the sticklebacks that live in
Lake Washington, the largest of three major lakes in the Seattle area.
Five
decades ago, the lake was, quite literally, a cesspool, murky with an
overgrowth of blue-green algae that thrived on the 20 million gallons of
phosphorus-rich sewage pumped into its waters each day. Thanks to a $140
million cleanup effort in the mid-'60s - at the time considered the most
costly pollution-control effort in the nation - today the lake and its
waterfront are a pristine playground for boaters and billionaires.

It's precisely that cleanup effort that sparked the reverse evolution,
Peichel and colleagues surmise. Back when the lake was polluted, the
transparency of its water was low, affording a range of vision only about
30
inches deep. The tainted, mucky water provided the sticklebacks with an
opaque blanket of security against predators such as cutthroat trout, and
so
the fish needed little bony armor to keep them from being eaten by the
trout.

In 1968, after the cleanup was complete, the lake's transparency reached a
depth of 10 feet. Today, the water's clarity approaches 25 feet. Lacking
the
cover of darkness they once enjoyed, over the past 40 years about half of
Lake Washington sticklebacks have evolved to become fully armored, with
bony
plates protecting their bodies from head to tail. For example, in the late
'60s, only 6 percent of sticklebacks in Lake Washington were completely
plated. Today, 49 percent are fully plated and 35 percent are partially
plated, with about half of their bodies shielded in bony armor. This
rapid,
dramatic adaptation is actually an example of evolution in reverse,
because
the normal evolutionary tendency for freshwater sticklebacks runs toward
less armor plating, not more.

"We propose that the most likely cause of this reverse evolution in the
sticklebacks is from the higher levels of trout predation after the sudden
increase in water transparency," said Peichel, whose Hutchinson Center lab
has established the stickleback as a new model for studying complex
genetic
traits. By examining multifaceted traits in the fish, such as body type
and
behavior, Peichel and colleagues shed light on the genetic networks at
play
in other complex traits, such as cancer and other common human diseases.

The ability of the fish to quickly adapt to environmental changes such as
increased predation by the cutthroat trout is due, Peichel believes, to
their rich genetic variation. The sticklebacks in Lake Washington contain
DNA from both marine (saltwater) fish, which tend to be fully plated, and
freshwater sticklebacks, which tend to be low-plated. When environmental
pressures called for increased plating, some of the fish had copies of
genes
that controlled for both low and full plating, and so natural selection
favored the latter.

"Having a lot of genetic variation in the population means that if the
environment changes, there may be some gene variant that does better in
that
new environment than in the previous one, and so nature selects for it.
Genetic variation increases the chance of overall survival of the
species,"
she said.

The researchers' findings challenge a widely held theory behind rapid
evolutionary change, the idea of "phenotypic plasticity" - when an
organism
can take on different characteristics independent of genetic influences.
Body type is one such example. "There is some genetic component to body
size, but if you eat more nutritious food as a child you're probably going
to grow taller than someone who has the same genes but may not have had as
good of a diet growing up," Peichel said. "Our findings challenge the
primary role of phenotypic plasticity in rapid evolutionary change."

The gene that controls for plating is called Eda, which comes in two
forms:
one causes low plating and the other complete plating. Peichel was the
first
person to home in on the neighborhood where the Eda gene lives while a
postdoctoral researcher in the laboratory of David Kingsley, Ph.D., at
Stanford University.

In humans, mutations in this gene cause a syndrome called ectodermal
dysplasia, a group of more than 100 inherited disorders that impact the
ectoderm, the outer layer of tissue involved in the formation of many
parts
of the body, including the skin, nails, hair, teeth and sweat glands.

"There's probably a developmental correlation between these external
structures in humans and the bony plates on the fish," Peichel said. "It
also looks like the Eda gene was probably important for human evolution
although we don't really know in what context," she said.

Source: Fred Hutchinson Cancer Research Center
http://www.physorg.com/news130073255.html

Posted by
Robert Karl Stonjek




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