Immune defense for the birds

Humans can declare what they bring from one country to another, but birds are another story.

Because they are such avid travelers, it is difficult to know what parasites various species of birds pick up, but on heavily populated islands in the world, it is evident that unfamiliar diseases are killing them off.

In order to determine the effect of such parasitic invasions, University of Utah biologists went to the Galapagos Islands, off the coast of Ecuador, to find large populations of finches to study. The bird is the same species that Charles Darwin observed in the 1830s to determine his evolutionary theory.

There are 15 species of finches in the Galapagos, all evolving from one common ancestor. U. biology professor Dale Clayton said the finches "figured prominently" in Darwin's theory about how new species survive. Now, they play an even more critical role in "survival of the fittest."

The findings of the U. study — published online Wednesday in PLoS ONE, a journal of the Public Library of Science — reveal that when a host species is invaded by parasitic organisms, defense systems can somehow evolve to fight off infection and eventual death. The question remains whether that immunity can increase fast enough to ward off destruction of the species.

The U. scientists discovered that the finches in the Galapagos have shown a propensity for developing antibodies that fight off nest flies and a specific pox virus, both of which have led to death in the species in other areas. The study is significant because "these finches are icons of evolution, and the icons are in danger of extinction," Clayton said.

"Wild species can respond to invasive parasites with which they have no history of association," he said of the evolutionary behavior. "The immune system has been activated."

The Galapagos is "the most famous group of islands that hasn't had any native birds go extinct yet," Clayton said. Native species on Hawaii, for example, he said, "have gone extinct because of humans," who introduced mosquitoes with malaria as well as predators such as cats and rats, and who destroyed habitat and hunted birds for feathers.

"It's what we call in evolutionary biology an arms race between the host and the parasite," he said. Current research aims to determine whether "the birds are able to fight back," Clayton said. "Do they have defenses, or have they just been blindsided because they have no evolutionary history with these parasites?"