SEATTLE 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 thats just because people havent 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.
Its 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 lakes transparency reached a depth of 10 feet. Today, the waters 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
|Contact: Kristen Woodward|
Fred Hutchinson Cancer Research Center