Tuesday, May 20, 2008

Evolution, devolution....

One of my friends was kind enough to send me a link to this article, and I thought I'd share it with the rest of you.

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

Adaptation coincides with the '60s cleanup of toxic pollution in Seattle's Lake Washington


It's an interesting case of evolution reverting itself, when living conditions changes.

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.


Of course, it's somewhat wrong to talk about reverse evolution, since the sticklebacks have undergone a evolutionary process - it's just that nature started to select for different aspects than it did when conditions were differently.

The findings have been published in Current Biology under the title Reverse Evolution of Armor Plates in the Threespine Stickleback by Kitano et al.

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