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Where Darwin Watched Beaks, WSU Looks At Antibodies

Charles Darwin saw a product of evolution in the beaks of finches. Researchers from Washington State University are now looking at the same birds’ immune systems to see evolution in action.

Jeb Owen, an assistant professor of entomology, and Marisa King, a zoology doctoral candidate, developed a test to see if the species of finches that Darwin studied more than 150 years ago are developing immunities to two exotic parasites, a virus and a nest fly. The test is the first to detect the antibodies that a wild bird marshals against specific parasites and has implications for the study of immunology, evolution and conservation.

The work, published this week in the online journal PLoS ONE, is also one of the most advanced looks yet at Galapagos Island finches. The iconic birds descended from a common ancestor and developed different beaks and other features that fueled Darwin’s thinking about how species evolve. Their value to science continues to this day, in part because humans settled the Ecuadoran islands later than most other remote places, delaying the introduction of foreign parasites and diseases.

But the birds are now being infected by two introduced parasites –a pox virus, which creates lesions on the birds’ unfeathered parts, and a nest fly, which can slow the growth of nestlings and even kill them.

Such scenarios—invasive pathogens attacking animals with no known defenses—have become commonplace around the planet as virtually every locale has become accessible to humans and exotic, pestilent hitchhikers. They have stimulated the field of ecological immunology, which investigates the tradeoffs in an organism’s response to a pathogen.

In a way, ecological immunologists are testing in the natural world Friedrich Nietzsche’s observation, “What does not destroy me, makes me stronger,” with a more nuanced view. Under the commonly held Nietzche view, a pathogen will kill a human or other animal unless it develops an immune response like antibodies, which in effect make it stronger. But immunologists understand that an immune reaction, like asthma, can in itself be deadly. The devil is in the details, many of which fell to Owen and King.

Researchers from the University of Utah

Blood samples drawn from Darwin finches were tested at WSU for antibodies/Photo courtesy of Sarah Huber, University of Utah

captured finches at two locations in the Galapagos, examined them for signs of the pox or flies, and drew teardrop-sized blood samples for analysis by Owen and King. The WSU researchers developed a way to place a diluted blood sample in a dish coated with proteins from the parasites and measure how well antibodies in the blood reacted.

Until now, researchers have only tested a wild bird’s immune response to a lab-designed stimulant. Typically they’ve used proteins called PHA, which are perhaps best known for making raw beans poisonous to humans. But such tests, said Owen, give only a vague idea of an animal’s immune response.

Researchers have also tested more specific pathogens on domestic birds like chickens, poor proxies for wild birds in their natural environment.

“The real usefulness of this,” said Owen, “is that now, instead of assessing this vague concept of what the immune system is doing, we are assessing directly this relationship between immune function and the parasite that is challenging the fitness of that animal.”

Such specificity has already given researchers new insights, he said.

Before this research, said Owen, it was thought the flies only impacted the nestlings. The larvae would only be in the nest and the nestling would have lesions.

“When we went and did our tests, we found that mothers are also developing an immune response,” he said. That will help researchers assess what price the mothers are paying in energy and resources, particularly when they’re already stressed by the rigors of rearing young. And to know a pathogen’s impact, researchers need to know who is paying and at what price.

Over time, researchers should be able to measure immune-system variations in different populations of birds and see how they affect their survival—a fundamental component of evolutionary selection. Researchers can also look for birds that are more resistant to pathogens. Owen said these might then be bred or transplanted as part of a conservation strategy.