Did learning to fly give bats super-immunity?

Not content with echolocation and being able to sense magnetic fields, when modern bats' ancestors learned to fly, they gained another superpower: immunity to some of the world's deadliest diseases.

Bats carry many diseases, including SARS and Ebola, but very few actually make them sick. For an animal of their size, they also age very slowly, usually being killed by external causes rather than age or disease.

But rather than just evolving to protect the animals from infectious diseases, this incredible immunity may have evolved in response to the extra stresses of flying.

The bat is the only mammal capable of flying long distances. This means that they use about 20 times more energy than other mammals of the same size during an average day. The by-product of generating the extraordinary amount of energy needed to fly are molecules called reactive oxygen species. These damage DNA by ripping off its hydrogen atoms.

DNA smasher

Christopher Cowled from the CSIRO Australian Animal Health Laboratory in Geelong, Victoria, Australia, figured that to avoid the cancer and premature ageing these DNA-smashing molecules would normally cause, bats had to have evolved a strategy to avoid the damage.

Comparing the genomes of two very different bat species, Cowled and colleagues found that the genes that detect and respond to DNA damage had undergone a sudden change around 88 million years ago, when bats' ancestor's first took to the skies. Because the change wasn't seen in the genomes of other mammals, Cowled attributes the change to the animals' newfound ability.

"We found genetic changes that are right in the intersection that handles DNA damage and initiates the frontline antiviral immune response," says Cowled. "We believe that flight was the initial trigger that led to improvement in the [immune] systems."

Disease beater

"What we're hoping is bats can do something better than humans can, and maybe we can strive to reproduce it," says Cowled. If we can manipulate the human immune response to be more like a bat immune response, maybe we will have a better chance of surviving diseases that bats are immune to, he adds.

Edward Holmes, an infectious disease expert at the University of Sydney in Australia describes this as a "breakthrough study" that reveals part of the reason why the immune system of bats differs from those of other mammals.

"This paper establishes the framework necessary to understand why bats are such an important source of emerging viruses," he says.

Journal reference: Science, DOI: 10.1126/science.1230835

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