Scientists discover asexual creature’s evolutionary ‘tool kit’

One microscopic organism has thrived despite remaining celibate for tens of millions of years, thanks to a neat evolutionary trick, researchers said.

Asexual reproduction has allowed duplicate gene copies of the single-celled creatures — called bdelloid rotifers — to become different over time. This gives the rotifers a wider pool of genes to help them adapt and survive, the researchers said in Friday's issue of the journal Science.

“It is like having a bigger tool kit,” Alan Tunnacliffe, a molecular biologist at the University of Cambridge, said in a telephone interview. “You can do the same job, but better.”
Other researchers had shown that the translucent, waterborne creatures could survive for 40 million years without sexual relations.

The question, Tunnacliffe said, was how the creatures found in pools of water accomplished this feat without the gene-swapping made possible by sexual reproduction.

“Sexual reproduction is supposed to be a good thing in evolution,” he said on Thursday. “So when you come across an organism like the bdelloid, which hasn’t engaged in sexual reproduction for tens of millions of years, you begin to question why sex is important.”

Every species of plant and animal that reproduces sexually has pairs of genes nearly identical to each other, with one of each pair coming from the mother and father.

These creatures get around that problem with the evolutionary trick that allows their genes to drift apart and evolve on their own, Tunnacliffe said, after using molecular cloning techniques.

“No sex means the genes can evolve in different directions,” he said. “It is like you have a bigger gene pool to select from for different functions in evolution.”

The theory of natural selection says sex mixes up the genes to cope with unexpected changes in a treacherous world. Some genetic changes are good and boost survival — for example, against new strains of disease — but others lead to conditions such as cystic fibrosis in humans.