How to Survive Without Sex: Rotifer Genome Reveals Its Strategies

How a group of animals can abandon sex, yet produce more than 460 species over evolutionary time, became a little less mysterious this week with the publication of the complete genome of a bdelloid rotifer (Adineta vaga) in the journal Nature.

Rather than the standard way of using sexual reproduction to weed out harmful mutations to its DNA, this tiny aquatic animal appears to have adopted other strategies to maintain lineages over millennia that aren't burdened by genetic damage or killed off altogether, says David Mark Welch of the Marine Biological Laboratory (MBL) in Woods Hole. Mark Welch and his MBL colleague, Irina Arkhipova, are the U.S. leads on the international project to sequence the rotifer genome and analyze what it reveals.

Neither males nor meiosis (cell division to produce sperm or eggs) have ever been observed in a bdelloid rotifer. Instead, the unfertilized eggs just divide to produce offspring. This reproductive strategy, which for most animals would be an evolutionary dead end, is borne out by the rotifer's genome, the structure of which "is completely consistent with what you would expect to see with a long-term absence of meiosis," Mark Welch says.

"It's hard to prove a negative, and we can never say there is no chance the rotifer is ever having sex. But it would have to be some kind of crazy meiosis," Mark Welch says. Another striking finding in the bdelloid rotifer genome was the extremely low number of transposons, "pieces of DNA sometimes called 'genetic parasites' that are capable of moving around the genome and causing harmful mutations," Arkhipova says.