Stickleback Fish Becomes An Unlikely Star Of Evolutionary Science

February 22, 2009

Release from: Sandi Doughton
The Seattle Times

In his voluminous writings, Charles Darwin made only brief mention of a little fish called the stickleback.

But 200 years after Darwin’s birth, the stickleback has become an unlikely superstar of evolutionary science.

Like the finches and tortoises of the Galapagos Islands that sparked Darwin’s theory, sticklebacks have adapted to myriad habitats in an evolutionary eye-blink. Scientists in Seattle, Canada and elsewhere now are using molecular techniques to study those adaptations, and their work is yielding the clearest insights yet into the way natural selection works at the genetic level.

In some cases, they find nature needs to tweak only a few genes to cause major changes in the stickleback body. Other studies show the fish can evolve to cope with new conditions in as little as 10 years. And though sticklebacks are different from people, there may be evolutionary parallels that could help explain human development and disease.

“The stickleback work is probably the best demonstration of natural selection in all its nuances that we have right now,” said evolutionary biologist Andrew Hendry of McGill University in Montreal. “It’s fusing the world of genetics and development with the worlds of ecology and evolution better than any other system I know of.”

University of British Columbia biologist Dolph Schluter was one of the first to see the potential in the innocuous-looking fish in his own backyard.

In the Pacific Northwest, three-spine sticklebacks are as common as cloudy days.

Freshwater sticklebacks are among the youngest species on Earth, which makes it easier to follow their evolutionary tracks. Their marine ancestors migrated inland when ice-age glaciers melted 10,000 to 15,000 years ago.

In their new freshwater homes, sticklebacks blossomed into dozens of varieties, each slightly different from those in the next drainage. But a few consistent changes occurred everywhere the fish adapted.

They shed some of the heavy armor plates that protect against ocean predators but seem to hinder quick escapes in freshwater; they lost belly spines that proved a handicap with insects grabbing at the young fish from below. Sticklebacks that live on lake bottoms are almost always lighter in color than their marine counterparts, probably for camouflage.

Those patterns repeat around the world. Researchers say that means it’s not chance, but natural selection, behind the wheel.

“One of the beautiful things about the stickleback is that the process of colonizing new lakes and streams from the ocean has played out countless thousands of times,” said Stanford University developmental biologist David Kingsley, who has led much of the genetic work. “You’ve got all these natural experiments replicated over and over again.”

To replicate those experiments — but in a controlled way — Schluter built more than 30 ponds on the University of British Columbia’s Vancouver campus, each up to 75 feet square. He jokingly calls the complex his “evolution accelerator.”

For several years, he and his students have been crossing and combining varieties of sticklebacks, throwing them in the ponds and keeping careful track as nature — and natural selection — takes its course.

But Schluter wasn’t able to peer inside the sticklebacks’ DNA until Kingsley and Katie Peichel, of Seattle’s Fred Hutchinson Cancer Research Center, offered up their expertise in molecular biology.

“The only way evolution can happen is through genetic changes that can be passed from generation to generation,” Peichel said. “We want to figure out what are the actual genes that cause these fish to have spines on their bellies, or not; to have (armor) plates or not have plates.”

By crossbreeding sticklebacks and examining their DNA, Kingsley, Peichel and their colleagues have done just that. They also discovered a gene that determines whether sticklebacks will have light or dark skin.

Humans share the stickleback gene for skin color. And, like sticklebacks, some of our ancestors evolved lighter skin as they migrated away from humanity’s African birthplace. The gene that causes sticklebacks to lose their pelvic spines may be linked to the loss of hind limbs in whales and manatees, and the crippling condition called club foot in humans. People with a mutant form of the stickleback armor gene lack teeth, hair or sweat glands.

“We think the stickleback is a great model for what’s going on in humans,” Peichel said.