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Asexual Solutions

It is widely known that Bdelloid rotifers are asexual, not that there's anything wrong with that, but how is it that these all –female metazoans have become so complex, and successful as a lineage?

A research team looking into the question found that the Bdelloid's genome is "a total mess," according to Discover's Razib Khan, a tangle of individual copies of genes so chaotic that pairing for meiosis and sexual reproduction are impossible.

Khan, reviewing a new paper in Nature, says the research proposes two ways that the Bdelloids manage to dodge the problem of Muller's Ratchet, the accumulation of deleterious alleles in the genomes of asexual critters.

While loss of sexual reproduction usually leads to "an evolutionary dead end" for metazoans, these Bdelloid rotifers break the mold, "as they appear to have persisted asexually for millions of years," the papers authors write.

They appear to lean heavily on gene conversion and horizontal gene transfer to keep bringing in new genetic material.

Lead author Alan Tunnacliffe at the University of Cambridge says the investigators found that up to 10 percent of the active genes in the Bdelloids come from bacteria, fungi, and algae, adding to "the weirdness of an already odd little creature," according to LiveScience.

"We don't know how the gene transfer occurs, but it almost certainly involves ingesting DNA in organic debris, which their environments are full of," Tunnacliffe says. "Bdelloids will eat anything smaller than their heads!"

Khan says that these almost obvious solutions for Bdelloid rotifer reproduction brings up the question of why more similar organism to not have the same profile.

"Many lineages have parthenogenetic branches. But few of them become as wildly successful as Bdelloid rotifers.
It would be curious if other sexual metazoans were to be found with the Bdelloid genomic profile," he writes.