How to Resist 80 Million Years without Sex

To survive in an ever changing environment filled with new viruses and bacteria, organisms developed sex, a method through which species get enough variation to withstand these conditions. That's why researchers were puzzled how a microscopic organism, bdelloid rotifers, has survived for nearly 80 million years without sex.

These asexual organisms reproduce by cloning, without males. Many other asexual organisms have been found, but they are believed to disappear quickly as they cannot adapt, as without sex the organisms lack the means to adapt over generations.

That's why the way bdelloid rotifers have survived for 80 millions of years was a puzzle. Bdelloids usually inhabit freshwater pools, but when deprived of water they can pass into a dehydrated state in which they stay for many years, experiencing almost complete water loss.

Due to proper conditions (water available), the rotifers turn back to life, without any ill effect. The new study reveals how Adineta ricciae, a species of bdelloid rotifer, has turned asexual to cope with dry conditions.

In organisms that reproduce sexually, each individual carries two copies (in a pair) of each chromosome per cell, one copy coming from the mother and one from the father. This means that genes in a cell are in pairs, one coming from the mother, one from the father. This means that two almost identical copies of each gene in each cell will result in two proteins which are often almost identical.

But the two copies of the gene lea in Adineta ricciae differ, generating proteins with various functions which defend the animal during dehydration. One lea protein defends essential proteins from clumping together during the cell's drying, while the other helps keeping the fragile cell membranes. It is the first time when this evolutionary strategy has been revealed in any asexual animal.

"We've known for a few years that gene copies that would have the same DNA sequence in sexual creatures can be quite different from each other in asexuals. But this is the first time we've been able to show that these gene copies in asexuals can have different functions. It's particularly exciting that we've found different, but complementary, functions in genes which help bdelloid rotifers survive desiccation. Evolution of gene function in this way can't happen in sexual organisms, which means there could be some benefit to millions of years without sex after all." said lead researcher Dr. Alan Tunnacliffe from the Institute of Biotechnology at the University of Cambridge.