Geoffrey E. Hill
The red, swollen, crusty eyes in this house finch are the result of a highly contagious infection caused by the bacterium Mycoplasma gallisepticum.
updated 2/10/2012 1:11:50 PM ET 2012-02-10T18:11:50

The bacteria responsible for the red, swollen, crusty eyes of a sick house finch, which can leave it unable to survive, evolve at an exceptionally fast rate — which is both bad and good news for the future of the songbird, researchers say.

The fast evolution means the bacteria can keep up with their hosts' immune systems. However, in the process of evolving, the bacteria have lost genes that may protect them from viruses. That's a weakness scientists could take advantage of to get rid of the bacteria, which have led to the death of thousands of house finches in the wild since the bacteria jumped species and started an epidemic in the 1990s.

Bird bacteria
The tiny bacteria, Mycoplasma gallisepticum, infected poultry before it adapted to the house finch population. The researchers analyzed several samples of the bacteria from different years of the epidemic (the mid-1990s, 2001 and 2007) and compared them with strains isolated from chickens and turkeys. They were able to determine that the bacteria likely jumped from the turkey population, a possibility that other researchers had suggested.

By analyzing genetic sequences, researchers discovered that the bacteria mutated 10 to 100 times more quickly than other species of bacteria, seemingly giving them an evolutionary advantage.

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"We were surprised at what a high rate it was; it's higher than most published estimates and on par with just a few estimates out there," study researcher Scott Edwards of Harvard University told LiveScience.

That wasn't all that was hiding in the bacteria's genome, however: "We were surprised to find that the bacteria's own immune system against viruses and phage was evolving," Edwards said. "The bacteria lost about 50,000 base pairs (of DNA); as a result of this, it loses some functions that were formerly advantageous" — such as its ability to fight off viruses.

Phage attack
The researchers said they aren't sure whether the loss of key immune-system genes was an artifact from the bacteria's move to the new host (perhaps the small population of bacteria that started the epidemic had already lost their immunity genes) or whether they lost them along the way because it somehow gave them an advantage in the house finches.

A bacterium's immune system defends against viruses called phage. Without the immunity, a virus could attack unimpeded and kill the bacterium. Researchers say the mycoplasma may no longer be able to fight off phage, though the researchers don't know enough about such viruses to really say what would make a good weapon.

"Who knows, maybe we could enlist some viruses to get rid of them," Edwards said. "That's one of the next things we want to do, look at how this loss of the immune system in the bacteria affected its susceptibility to phage."

The study was published Thursday in the journal PLoS Genetics.

You can follow LiveScience staff writer Jennifer Welsh on Twitter @microbelover. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.

© 2012 All rights reserved.

Explainer: 7 signs of evolution in action

  • Image: scroll fragment
    Spencer Arnold  /  Getty Images file

    British naturalist Charles Darwin's groundbreaking 1859 book, "The Origin of Species," proposed the theory that species evolve over time through the process of natural selection. Organisms most suited to their environment survive and reproduce, passing on their advantageous traits to offspring. Organisms that cannot compete go extinct. Though this theory remains a hot potato in the culture wars, it forms the foundation of modern biology. Click the "Next" arrow above to see seven signs of evolution in action.

    — By John Roach, contributor

  • Darwin's finches evolve

    Image: Elah Fortress ruins
    B. Rosemary Grant  /  Science via AP file

    The seed-crushing bills of little songbirds called finches, which were adapted to various niches throughout the Galapagos Islands, proved integral to the formulation of Darwin's theory of evolution by natural selection. And the birds haven't stopped evolving. For example, the medium ground finch (Geospiza fortis), shown here, recently downsized its beak to exploit small seeds more efficiently after a larger finch arrived on its island and began competing for food. The smaller beaks on the smaller birds allowed them to thrive, while the big birds ate all the big seeds and nearly went extinct, scientists say.

  • Humans influence natural selection

    Image: pottery shards

    Is human activity "natural"? Scientists say human activity is indeed affecting the evolution of other species. In one example, the human preference for large snow lotus plants, which are used in traditional Tibetan and Chinese medicine, has meant that only the smaller plants go to seed. Hence, the snow lotus is getting smaller. In another example, scientists have found that human preference for trophy game such as big fish and caribou is driving these species to become smaller and reproduce at younger ages.

  • Human evolution speeding up?

    Image: water flows through remains of Siloam Pool site
    Hulton Archive  /  Getty Images file

    With more people crowding into ever more ecological niches over the past 10,000 years, humans appear to be evolving more rapidly than in the distant past, according to scientists. What's more, as people adapt to different regions, cultures and diets, they are becoming increasingly different from people elsewhere. For example, Europeans have evolved a tolerance for dairy products into adulthood, whereas people in China and most of Africa have not.

  • Butterflies evolve resistance to killer bacteria

    Image: Dead Sea scrolls
    Sylvain Charlat / Science

    A population of tropical butterflies on a South Pacific island evolved resistance to a killer bacteria in the span of a single year — a blink of the eye in evolutionary time. The bacteria infects females and selectively kills males before they hatch. The strategy reduced male Blue Moon butterflies to just 1 percent of the population. But just 10 generations later — a year's time — males made up nearly 40 percent of the population. Scientists said the rebound is due to the evolution of a so-called suppressor gene that keeps the killer bacteria in check.

  • Toxic toad evolves longer legs

    Image: sarcophagus
    Ben Phillips

    A toxic toad, introduced in 1936 to wipe out a beetle species wreaking havoc on Australia's sugar cane crop, has become an uncontrollable pest itself, evolving longer legs to help it hop across the country at an ever-increasing clip. For their first 20 years or so in the country, they spread at a pace of 6 miles per year. They now cruise at about 30 miles per year. Why? Researchers found that the toads leading the cross-country march had legs that were 6 percent longer than those of the stragglers. The added length gives more speed, which permits the long-legged toads to secure the best habitat at the newly conquered terrain.

  • Intermediate form supports flatfish evolution

    Image: drainage channel

    Flounder, sole, halibut and other flatfish have long struck biologists as evolutionary oddities: Both their eyes are on one side of the head, an adaptation that allows them to lie flat on the ocean bottom while keeping their eyes on the lookout for passing prey. The transition happens in the youth of flatfish, one eye migrating up and over the top of the head. Opponents of evolution argued that this curious anatomy could not have evolved gradually, as suggested by the theory of natural selection. That's because there would be no advantage for an intermediate form — a fish with an only partially migrated eye. But now scientists have found those intermediate forms in museum collections. The 50 million-year-old fossils, including Heteronectes chantei shown here, have a partially displaced eye.

  • Lizards lose limbs

    Image: archaeological site in Masada
    Mark Hutchinson

    Australian lizards called skinks are dropping their limbs to become more like snakes. And, according to a genetic family tree, some skinks have gone snaky in just 3.6 million years, relatively fast in evolutionary time. Scientists said the skinks' lifestyle appears to be driving the change: They spend most of their time swimming through sand or soil. Limbs are not only unnecessary for this, they may be a hindrance. Once a skink goes snaky, they never go back, the researchers add. One of the snakelike skinks is shown here.


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