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The long reach of a gene

Can a few tree genes call most of the shots in an ecosystem?

Many biologists would say “no” – trees, after all, are just one part of a very complex web of life. But trees are the dominant players in many ecosystems, and tree genes may have far-ranging effects on other organisms in an ecosystem, says Rick Lindroth, an ecologist in the Department of Entomology at the University of Wisconsin-Madison.

Lindroth is a co-investigator in a $5 million Frontiers in Integrative Biological Research grant from the National Science Foundation. This FIBR project examines how the genetics of certain trees affect the biological communities and ecosystems of which they are a part.

Historically, the study of genetics has been limited to single organisms and populations. Community genetics reaches further, examining the genetic linkages among species, communities and entire ecosystems, Lindroth explains. “The extent of these linkages is unknown, but likely to be very important. This is especially so in a world where human impacts, including disturbance, habitat fragmentation and the introduction of exotic species, are disrupting ecosystems that have evolved for millions of years in the absence of these perturbations,” he says.

“We are entering the realm of genetics beyond the level of populations, to understand how communities and ecosystems are structured and function. Ecologists have historically tended to believe that the effects of single genes become so diffuse at the community and ecosystem levels that they are imperceptible. Our work is showing that is not necessarily the case.

“Our group thinks that the genetic constitution of dominant players – trees, for example – in an ecosystem can have significant consequences for other species in the system. We think the underlying genetics of the dominant players may drive how whole communities are assembled, and how component species interact.

“We might have whole communities and ecosystems that evolve together,” Lindroth says.

For this project, researchers are planting thousands of cottonwoods along the Colorado and Weber rivers in Utah, and are studying natural cottonwood stands in Utah and Arizona. Lindroth”s group plans to study the effects of tree genetics on leaf chemistry.

“We”re trying to show how plant genetics mediated through chemistry affects the ecosystem,” Lindroth says. According to Stuart Wooley, a postdoctoral researcher on the project, “a tree”s genetics determines its chemistry, which determines the insect species that occur on the tree. Insects provide food for birds and thus influence the bird community. Beavers, which have large effects on habitat structure, choose which trees they cut based on the tree”s chemistry. For example, beavers favor low-tannin trees, so when they”re around you”re going to lose the low-tannin trees and have more high-tannin trees remain.

“We take trees of different genotypes, grow them together, and look for unique assemblages of insects varying by tree genotype. We use very large tree plantations with different genetic strains of cottonwoods. The data should help researchers create spatial mosaics of ecosystem function because of the different strains” chemistries,” says Wooley.

Why cottonwoods? For one thing, the cottonwood genome was recently sequenced. “Now that we know the cottonwood genome, we might link large-scale processes to particular genes in the cottonwood genome,” Lindroth says. “And cottonwoods grow rapidly, which is a big benefit when studying tree genetics.”

FIBR is a premier, cross-cutting program in biology that supports highly innovative and broadly integrative research. Ten principal investigators, all with different expertise, are collaborating on this project. “In ecology, many emerging problems are so complex that they can”t be handled by a single individual or institution,” Lindroth says. “This work brings together soil microbiologists, geneticists, terrestrial and aquatic ecologists, and modelers.” The lead investigator for this FIBR project is Tom Whitham, director of Northern Arizona University”s Merriam-Powell Center for Environmental Research. The other researchers hail from the United States, Canada and Australia.