SSS 2010-01-29（在线收听）

Organisms evolved sexual reproduction so they could stay one step ahead of parasites. Or so the theory goes. But what about beasties that make babies without sex? How do they escape infection? A study in the journal Science suggests that for bdelloid rotifers, the answer is blowin’ in the wind.

Biologists believe that sex offers an evolutionary advantage because it promotes genetic diversity. Coming up with fresh new gene combinations should allow organisms to outsmart parasites, which are also continuously evolving. But if that theory is correct then bdelloid rotifers, freshwater invertebrates that haven’t had sex in at least 30 million years, should have been parasited into extinction long ago. Yet here they are, alive and well.

To find out why, scientists infected rotifers with a deadly fungus. And they found that bdelloid rotifers can shake the infection by drying out, drifting away and then rehydrating once they land someplace moist but fungus-free. The fungi don’t survive the desiccation, so the longer the bdelloids stay dry, the better off they be.

So for celibate rotifers that want to stay clean, a good long dry spell is just what the doctor ordered.

—Karen Hopkin