Evolutionary Engineering of an Ecosystem

Wednesday, April 1 2009

April 1, 2009

Written by Ken Kingery 

MOSCOW, Idaho – Scientists at the University of Idaho have demonstrated experimentally that a single divergent branch on the evolutionary tree can drastically alter an ecosystem in a relatively short time span.

In a paper recently published online by Nature, Luke Harmon, professor of biological sciences, used the threespine stickleback, a species of fish Harmon dubs a “champion of evolution,” to demonstrate the unpredictable impact that evolution can have on an ecosystem. The research was part of a worldwide collaborative effort between the University of Idaho, Washington University of St. Louis in Missouri, Switzerland’s Federal Institute of Aquatic Science and Technology, and the University of British Columbia in Canada.

“This phenomenon is called ecosystem engineering,” said Harmon. “It’s the way a species can engineer their environment through the effects of what they eat and how they live have on their habitat.”

Threespine stickleback fish commonly are found in both salt and fresh waters throughout the temperate northern hemisphere, including the lakes and streams of British Columbia. What makes them scientifically relevant is their evolution into two distinct species within the past 10,000 years – biologically speaking a relatively short time period.

New species form all the time, but what makes stickleback so interesting is that they’ve done it multiple times in completely separate ecosystems. Scientists don’t know exactly what causes this repeated speciation, but they suspect it is some specific, common traits between the ecosystems in which the fish live.

“The traditional way of thinking for evolutionary biologists is to wonder what characteristics of the lakes might have influenced their evolution,” said Harmon. “But we wanted to flip that question on its head and ask what effect evolution in a species might have on its environment.”

To answer this question, Harmon introduced the two species of stickleback to large aquatic tanks designed to mimic lake ecosystems. Some tanks were filled with limnetic sticklebacks that are smaller, surface dwellers with narrow mouths, and some tanks were filled with benthic sticklebacks that are larger, bottom-feeders with a wide gape.

Still more tanks were filled with either a mixture of the two species or stickleback from a generalist population, which is similar in form to the probable ancestor of the two species.

The results over a 10-week period were obvious.

“You could just walk into the experimental area and tell which tanks had which fish,” said Harmon. “The tanks just looked different.”

Some tanks were much greener than the others, and it was always tanks with the generalist stickleback present. Harmon expected the reason to be related to trophic cascades, where one fish species eats all of the other plant-eating organisms in the tank, resulting in more plants. But the real reason was much more complex.

The tanks with generalist stickleback had more aquatic plants, such as algae, and clearer water due to their feeding behavior. This seemingly small detail caused the water in their tanks to have smaller dissolved organic substances, which originate from decaying organic materials, and to be more transparent. Despite their common ancestry, the stickleback species’ altered evolutionary histories caused major differences in how they engineer the light environment of their aquatic ecosystems. The altered light environment then subsequently caused even more differences like the amount of chlorophyll in the water and the species of zooplankton present.

“This is a good example of speciation in a rapid time interval and how it can strongly affect ecosystem functions,” said Harmon. “Here, we’re showing that a really young species with recent diversification can have a big impact on an ecosystem. It ties into a broader body of literature showing that species diversity matters in important ways.”

Harmon’s full article can be found on Nature’s Web site, www.nature.com/nature, or at http://dx.doi.org/10.1038/nature07974.
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About the University of Idaho
Founded in 1889, the University of Idaho is the state’s flagship higher-education institution and its principal graduate education and research university, bringing insight and innovation to the state, the nation and the world. University researchers attract nearly $100 million in research grants and contracts each year; the University of Idaho is the only institution in the state to earn the prestigious Carnegie Foundation ranking for high research activity. The university’s student population includes first-generation college students and ethnically diverse scholars. Offering more than 150 degree options in 10 colleges, the university combines the strengths of a large university with the intimacy of small learning communities. For information, visit www.uidaho.edu.

Media Contact: Ken Kingery, University Communications, (208) 885-9156, kkingery@uidaho.edu

About the University of Idaho
The University of Idaho helps students to succeed and become leaders. Its land-grant mission furthers innovative scholarly and creative research to grow Idaho's economy and serve a statewide community. From its main campus in Moscow, Idaho, to 70 research and academic locations statewide, U-Idaho emphasizes real-world application as part of its student experience. U-Idaho combines the strength of a large university with the intimacy of small learning communities. It is home to the Vandals. For information, visit www.uidaho.edu.