How flight helped bats become invincible to viruses

The mammals carry immune adaptations that emerged when their ancestors took to the skies

Bats produce harmful chemicals while flying, which might have driven them to evolve resistance to viruses.Credit: Marko König/imageBROKER via Alamy

Bats’ ability to swoop and soar through the sky might have given them another ‘superpower’ — invincibility to most viruses.

Around the time that bat ancestors evolved powered flight, their genomes picked up immune adaptations that can quell viral infections, finds a study of 20 bat genomes, including of species that carry the coronaviruses most closely related to SARS-CoV-2.

Bats — the only flying mammals — are suspected or known reservoirs for a horde of deadly viruses, including rabies, Ebola, Marburg and SARS-related viruses, which circulate in horseshoe bats (Rhinolophus) in southeast Asia. Field and laboratory studies suggest that bats rarely become ill from these viruses and don’t mount the harmful immune overreactions seen, for instance, in people with severe COVID-19.

“There’s something unique about bats,” says Aaron Irving, a comparative immunologist at the Zhejiang University–University of Edinburgh Institute in Haining, China, who co-led the study, published¹ on 29 January in Nature. “When they are infected, generally, they’re quite healthy. They somehow evolved the right way to control their immune responses without going overboard.”

Immunity secrets

To uncover secrets to bat immunity, a team led by Irving and Michael Hiller, an evolutionary genomicist at the Senckenberg Research Institute in Frankfurt, Germany, sequenced the genomes of ten bats, including four horseshoe bat and three species part of a family called hipposiderids, all of which are coronavirus reservoirs. The researchers then analysed these along with ten previously sequenced bat species from other parts of the family tree.

Compared with 95 other mammal species, bats had especially high numbers of immune genes, with changes indicative of natural selection. Some of these alterations were limited to individual branches of the bat family tree, hinting that they evolved after the group began diversifying. But many immune adaptations were shared by all bats, suggesting that they emerged in a common ancestor of all bats — and at around the same point that fossil evidence has suggested that powered flight evolved in the animals.