Bdelloid rotifers are one of the strangest of all animals. Uniquely, these small, freshwater invertebrates reproduce entirely asexually and have avoided sex for some 80 million years. At any point of their life cycle, they can be completely dried out and live happily in a dormant state before being rehydrated again.
This last ability has allowed them to colonise a number of treacherous habitats such as freshwater pools and the surfaces of mosses and lichens, where water is plentiful but can easily evaporate away. The bdelloids (pronounced with a silent ‘b’) have evolved a suite of adaptations for surviving dry spells and some of these have had an unexpected side effect – they’ve made the bdelloids the most radiation-resistant animals on the planet.
Ionising (high-energy) radiation is bad news for living cells. Far from granting superpowers, it damages DNA, often completely breaking both strands of the all-important molecule. If you think of DNA as a recipe book for the various parts of a living thing, the double-stranded DNA breaks that are caused by ionising radiation are like tearing the book up into small chunks.
Absorbed doses of radiation are measured in Grays and ten of these are more than enough to kill a human. In comparison, bdelloids are a hundred times harder. Eugene Gladyshev and Matthew Meselson from Harvard University found that two species shrugged off as much as 1,000 Grays and were still active two weeks after exposure.