Academics and Research / Magazine Feature

DU genetics center studies trumpeter swan populations

A new study by DU’s Rocky Mountain Center for Conservation Genetics and Systematics (RMCCGS) is helping wildlife conservationists manage western trumpeter swan populations.

Before their feathers became a fashion accessory in the late 1800s, the swans (Cygnus buccinator) lived throughout North America. By the 1930s, hunting had reduced them to a couple of small flocks in Alaska, Alberta and the tri-state area of Idaho, Wyoming and Montana.


Today, the swans are making a comeback under the management of the U.S. Fish and Wildlife Service (FWS) and the Canadian Wildlife Service. For administrative purposes, the agencies divide the natural range of the swans into two populations, the Pacific Coast Population and the Rocky Mountain Population, which includes the Tri-State Flock.

In 2001, FWS turned to DU’s conservation center to determine if this administrative division reflects actual genetic differences. Of particular interest was a small population area near Yellowstone National Park (Tri-State Flock) that, unlike other trumpeter swans, does not migrate, and the flock is not growing. Officials wondered if it is a distinct subspecies, or if inbreeding accounts for its lack of wanderlust.

Sara Oyler-McCance, biology assistant research professor and conservation geneticist with the U.S. Geological Survey, and Tom Quinn, biology associate professor, were co-principal investigators for the four-year, $242,259 study, which concluded last quarter. Biology master’s candidate Leah Berkman and Findley Ransler, staff research associate, completed the team.

“We sampled throughout the natural range and determined the distribution of genetic variation,” Oyler-McCance explains. “We enlisted volunteers from the Fish and Wildlife Service, the Canadian Wildlife Service and the Trumpeter Swan Society.”

The volunteers drew blood and collected feathers and non-viable eggs. The DU team examined each sample’s mitochondrial DNA, which reveals maternal genetic characteristics, and nuclear DNA, which carries genetic markers from both parents. An exacting process called DNA sequencing determines the order of paired nucleic acids, called base pairs. Berkman sequenced more than 1,000 base pairs of mitochondrial DNA. A separate technique to analyze nuclear DNA involved highly repetitive fragments of DNA called microsatellites. Ransler characterized each individual with 17 such microsatellite markers.

The DNA analysis revealed that although the Pacific Coast and Rocky Mountain populations have significant genetic differences, the two groups do interbreed where their territories overlap. The Tri-State Population is genetically consistent with other Rocky Mountain birds.

Oyler-McCance believes their non-migratory behavior is learned, because the population isn’t genetically different or particularly inbred. In fact, Canadian swans visit the Tri-State Flock each year, and the resulting “summer romances” may strengthen the gene pool. Flock numbers probably remain stable because the annual visitors also deplete the available food, she adds.

Knowing the different swan populations’ genetic composition is important to repopulation efforts, Oyler-McCance confirms.

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