In what is an unexpected development, an asexual microscopic animal called bdelloid rotifer carries numerous pieces of foreign DNA in its genome, scientists at the Marine Biological Laboratory (MBL) have revealed.
Lead researchers Irina Arkhipova and Matthew Meselson have unveiled evidence for massive horizontal gene transfer from bacteria, fungi, plants etc. into the bdelloid rotifer genome in a study report, published in the journal Science.
The researchers say that, while horizontal gene transfer is common in bacterial species, the study they carried out with colleagues from Harvard University is the first to show this happening on a massive scale in the animal kingdom too.
"It is quite amazing that bdelloids are able to recruit foreign genes, which were acquired from remarkably diverse sources, to function in the new host. Bdelloids may have the capacity for tapping into the entire environmental gene pool, which may be of (evolutionarily) adaptive significance during expansion into new ecological niches, and may even contribute to bdelloid speciation," says Arkhipova.
She says that the finding may help to explain why bdelloids have managed to diversify into more than 360 species over 40 million years of evolution, despite being exclusively asexual.
She also says that the bdelloid's ability to incorporate foreign DNA from their environment makes her feel that it may also pick up DNA from other bdelloids, which is almost as good as having sex.
As to what causes the bdelloids's germline to be so exposed to environmental exchange, Arkhipova says the reasons "are all speculative. But we talk about this a lot!"
She believes that the bdelloid's unusual ability survive total desiccation (drying out), which is fatal for most organisms, may help understand how it gobbles up such a variety of genes from its environment and incorporates it into its genome.
During the desiccation phase, Arkhipova says, "you would imagine there is potential for membrane damage and DNA damage in the rotifer. And not only the rotifer desiccates, but also everything it just consumed."
If the DNA of both the rotifer and its food are broken up during desiccation, she adds, "this would provide an opportunity for the (foreign) DNA to enter the rotifer's germ line. During rehydration, the DNA breakage is somehow repaired, and the foreign DNA may get incorporated."
Arkhipova has revealed that this idea is inspired by the recent work by Meselson and Harvard graduate student Eugene Gladyshev showing that bdelloids are exceptionally good at recovering from ionizing radiation, which shatters their DNA.
She believes that the rotifers' talent for repairing DNA breaks may have evolved due to their desiccation-prone lifestyle.