Life under one tree's rule?

Tom Whitham and trees go way back. As a youngster, he walked along rows of trees, picking out ones that had an oddly shaped branch or some other peculiar trait. His family, which has been in the nursery business since 1863, would try to propagate these trees to see if the differences he spotted were genetic - a key step to developing and patenting new varieties.

"Very early on, I came to the realization that, hey, there's a lot of genetic variation out here," says Dr. Whitham, director of Northern Arizona University's Merriam-Powell Center for Environmental Research.

Now, Whitham and colleagues in the US, Canada, and Australia are on the trail of a more ambitious proposition - that a gene or a set of genes from a single species can lay the foundation for an entire ecosystem.

That idea borders on heresy for many biologists, who argue that any one gene plays only a small role in the complex interactions of ecosystems. But if the researchers are right, then the genetic diversity of one dominant species can have a huge impact on the biological riches of its surroundings. And conservationists may have to take a new look at everything from preserving endangered species to evaluating the effects of genetically modified crops.

"When we talk about conserving genetic diversity, it's all focused around rare and endangered species," Whitham says.

"Nobody has really argued the importance of preserving genetic diversity in dirt- common species. If you want to conserve a community, you really need to be worried about conserving the genetic variation in dominant species."

The test subjects for the theory: cottonwoods in the American West. Previous experiments by Whitham and his collaborators suggested that a single cottonwood gene could influence thousands of organisms in the larger ecosystem.

Now, in cooperation with the US Bureau of Reclamation, the state of Utah, and local conservation groups, Whitham and his colleagues are providing thousands of cottonwood saplings for planting along segments of the Colorado and Weber Rivers that these groups are trying to restore to ecological health. These will become test sites for the experiment as well. In addition, the team is using thousands of other, more mature cottonwood in stands at sites in Utah and Arizona. Armed with the fully sequenced cottonwood genome, the group over the next five years will closely measure how the expression of genetic traits in different varieties of cottonwoods affects everything from formation and decomposition of leaves to the variety of microbes, insects, and other organisms in the area.

The notion that organisms in an ecosystem interact and rely on each other has a long pedigree, acknowledges Richard Lindroth, an entomologist at the University of Wisconsin and one of the project's principal investigators. Since "genetics underlies everything in biology, we would think that at some level all of these interactions and associations have a genetic component."

But trying to establish links genetically - especially tying them to a specific gene or segment of a genome in a dominant species - has been viewed as a fool's errand, Dr. Lindroth suggests.

"Ecologists have long thought that as you work your way up from genes to a whole organism to whole populations of organisms to a whole communities of different species of organisms, the effects of a particular gene would be completely swamped out" by other factors, he says. "You wouldn't find the trail of a particular gene and track it all the way back to a particular plant."

But that isn't necessarily so, he continues. "In ecologically dominant species such as cottonwood, you can have specific genes that have a profound impact on the entire community. You don't lose the trail of cause and effect as you bring in additional species or the effects of the abiotic environment."

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