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To study Galápagos cormorants, a geneticist gets creative

Scientist calls on community to get DNA samples from bird species

By
7:52am, September 19, 2016
cormorants

GROUNDED  Unlike short-winged Galápagos cormorants (left), double-crested cormorants (right) and all other species have a wingspan meant for flying.

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Galápagos cormorants are the only flightless cormorant species. Their wings are too small to lift their heavy bodies. To trace the genetic changes responsible for the birds’ shrunken wings, Alejandro Burga needed DNA from the grounded bird and from a few related species. For the UCLA evolutionary geneticist, getting the right DNA was a yearlong effort.

After Galápagos cormorants (Phalacrocorax harrisi) split off from other cormorants, their wings shrunk to 19 centimeters long and their bodies grew to 3.6 kilograms, not a flying-friendly combination. Burga suspected he would have difficulty getting permission to collect DNA from the endangered birds. So he e-mailed “anybody who had ever published anything on cormorants” in the last 20 years, he says.

He found disease ecologist Patricia Parker of the University of Missouri-St. Louis who had collected blood from Galápagos cormorants in 2000 to monitor the spread of pathogens. Getting to the islands takes special permission, long flights and boat trips, but getting DNA from the meter-tall birds wasn’t hard.

“They’re sluggish, and they just sit there and look at you,” Parker says. She shared DNA that had been sitting in her lab refrigerator for more than a decade. Burga used it to reconstruct the cormorants’ genetic instruction book, or genome.

Next he needed comparison DNA from closely related species, such as the double-crested cormorant — a goose-sized waterbird with a broad wingspan. The bird is protected under a migratory bird treaty between the United States and Canada. Since Burga couldn’t just trap one and collect DNA, he got creative. He tried to extract DNA from preserved specimens at the Natural History Museum of Los Angeles County, but the genetic material was unusable. The San Diego Zoo sent samples of a too-distantly related great cormorant. An international bird rescue facility in Los Angeles notified him when someone found a dead cormorant on the beach. Burga rushed over, but the bird was a Brandt’s cormorant — also too far removed in the family tree to be of use.

One e-mail chain led to Paul Wolf, a U.S. Department of Agriculture wildlife disease biologist monitoring Newcastle disease virus in double-crested cormorants in Minnesota. With a special permit, Wolf removed one double-crested cormorant egg from a nest. The egg was at just the right stage of development — when the wings were beginning to grow — to determine which genes are active during wing development. Two down, two to go.

While on Alaska’s Middleton Island studying seabird parasites, Andrew Ramey of the U.S. Geological Survey collected two eggs from pelagic cormorants for Burga.

Burga also enlisted Claudio Verdugo, a molecular epidemiologist at Universidad Austral de Chile in Valdivia. Bird samples can’t be transported between countries because of fears of disease spread. So Burga sent chemicals and protocols to Verdugo, who took DNA from another species, the neotropic cormorant, and sent it to Burga.

With DNA from four cormorant species in hand, Burga and his newfound friends learned that the Galápagos cormorants’ stubby wings result, in part, from mutations in specific genes that encourage limb growth (SN: 6/11/16, p. 11). Burga is now studying how evolution grounded other birds.

Citations

A. Burga et al. Loss of flight in the Galapagos cormorant mirrors human skeletal ciliopathies. bioRxiv.org. Posted July 2, 2016. doi: 10.1101/061432.

Further Reading

T.H. Saey. How the Galápagos cormorant got its tiny wings. Science News. Vol. 189, June 11, 2016, p. 11.

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