Gone with the wind

The evolutionary secret of an asexual invertebrate that should have gone extinct long ago has been discovered by scientists – they are microscopic escape artists.

Bdelloid rotifers evade parasites and pathogens by drying up and floating away on the wind according to researchers from Cornell University. When exposed to fresh water, they rehydrate and come back to life.

How rotifers have been able to survive for so long has puzzled scientists who have been studying rotifers in the hope of gaining clues to the evolutionary advantage of sexual reproduction. It was thought sex produced fresh genetic combinations that allow animals to fight off evolving pathogens and parasites, but bdelloids have survived for millions of years, fending off enemies without sexual reproduction.

The recent discovery by doctoral candidate Chris Wilson and Paul Sherman, professor of neurobiology and behaviour has answered the mystery of the bdelloids’ ancient asexuality and success.

“These animals are essentially playing a game of evolutionary hide and seek,” said Sherman, “They can drift on the wind to colonise parasite-free habitat patches where they reproduce rapidly and depart again before their enemies catch up. This effectively enables them to evade biotic enemies without sex, using mechanisms that no other known animals can duplicate.”

To study bdelloid adaptations, Sherman and Wilson infected populations of rotifers with deadly fungus. They dried out infected populations for varying lengths of time before rehydrating them and found the fungi were more sensitive to dehydration than the rotifers. The longer the rotifers were dried out the higher their survival rate.

In a second experiment, dried fungus-infected rotifers were placed in a wind chamber. The scientists observed that the rotifers were able to disperse without the fungi and establish parasite-free populations, leading them to conclude that bdelloids can continuously establish new, uninfected populations.